出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers  

Accurate evaluation of neutron leakage dose plays a critical role in radiation protection for accelerator-based boron neutron capture therapy (AB-BNCT). This study reports the experimental validation of a neutron detector system for direct measurement of the neutron ambient dose, H*, in AB-BNCT irradiation fields. The system comprises an S-detector for detecting low-energy neutrons and an F-detector for higher-energy neutrons, with sensitivity extending up to 28 MeV. Detector geometries were optimized using Monte Carlo simulations to reproduce the fluence-to-H* conversion coefficients recommended in the ICRP Publication 116. Prototype detectors were tested in standard neutron fields, including thermal, monoenergetic, and fast neutron sources. The measured detector responses agreed well with calculated values, with deviations ranging from −13% to +4% for response and from −25% to −2% for dose response relative to ICRP values. These results demonstrate the suitability of the developed detector system for evaluating ambient neutron dose in AB-BNCT environments.

DOI： 10.35848/1347-4065/ae59d9

Open Access

Scopus

出版者・発行元：Journal of the Electrochemical Society  

In this study, we examined the corrosion resistance of Ru<inf>57</inf>Mo<inf>14.25</inf>W<inf>23.75</inf>Fe<inf>5</inf>, Ru<inf>54</inf>Mo<inf>13.5</inf>W<inf>22.5</inf>Fe<inf>10</inf>, and Ru<inf>48</inf>Mo<inf>12</inf>W<inf>20</inf>Fe<inf>20</inf> alloys in inorganic acids. The alloys were fabricated using the dewetting micro-pulling-down and plasma-melt stamping methods. Immersion tests in H<inf>2</inf>SO<inf>4</inf> at 300 °C for 24 h indicated that Ru-Mo-W-Fe alloys exhibit better corrosion resistance (<0.17 mm y⁻¹), compared to conventional corrosion-resistant materials (>10 mm y⁻¹). Immersion tests at 25 °C in 5% HCl for 72 h and at 100 °C in 50% HF for 24 h also indicated that Ru-Mo-W-Fe alloys are highly corrosion resistant. Electrochemical tests in 1 M HCl and 1 M H<inf>2</inf>SO<inf>4</inf> revealed an increase in the anodic current and the formation of a low charge transfer resistance passive layer corresponding to alloying Fe. XPS analysis revealed that the primary corrosion product formed during polarization of Ru-Mo-W-Fe alloys in 1 M H<inf>2</inf>SO<inf>4</inf> was WO<inf>3</inf>. Notably, WO<inf>3</inf> is kept passivated on pure W during the corrosion in H<inf>2</inf>SO<inf>4</inf>; however, it is not kept passivated when present on Ru-Mo-W-Fe alloys.

DOI： 10.1149/1945-7111/ae4cd0

Open Access

Scopus

出版者・発行元：Chemical Physics Letters  

We achieved 61 % ¹H polarization at room temperature and in 0.64 T via Dynamic Nuclear Polarization using photoexcited triplet electrons (Triplet-DNP). Dibenz[ a, h ]anthracene was introduced as a new host for pentacene- d <inf>14</inf>, providing a long spin-lattice relaxation time ( T <inf>1</inf>) exceeding 2 h. Single crystals doped with 0.05 mol% pentacene- d <inf>14</inf> were grown by the Bridgman method and cut to ∼1 mg for experiments. The ¹H polarization buildup and relaxation measurements indicated that paramagnetic relaxation dominates over spin-lattice relaxation. Finally, potential applications of room-temperature hyperpolarization, i.e. , nuclear ordering and radiation-tolerant polarized targets, were discussed.

DOI： 10.1016/j.cplett.2025.142606

Scopus

出版者・発行元：Materials Today Physics  

Novel neutron Li<inf>2</inf>Hf(Br,I)<inf>6</inf> scintillators were developed, and their luminescence and scintillation properties were investigated both experimentally and via density functional theory calculations. The development of conventional neutron scintillators has been dominated by materials with emission wavelengths in the range of 400–500 nm that have wavelength sensitivity of photomultiplier tubes (PMTs). However, with the recent emergence of detectors having higher quantum efficiencies than PMTs, such as Si-based photodetectors, there is a need for neutron scintillators with red-to-near-infrared (red/NIR) emission wavelengths that match the wavelength sensitivity of these detectors. Therefore, this study demonstrates that Li<inf>2</inf>Hf(Br,I)<inf>6</inf> exhibits self-trapped exciton emission under both X-ray and thermal neutron irradiation, with an emission peak at approximately 650 nm, which is 100–200 nm longer than the corresponding peak wavelength of conventional neutron scintillators. The emission wavelength of Li<inf>2</inf>Hf(Br,I)<inf>6</inf> matches the wavelength sensitivity of Si-APD. In addition, Li<inf>2</inf>HfBr<inf>4</inf>I<inf>2</inf> is the first neutron scintillator to combine emission in the red/NIR region with a high light output of approximately 40,000 photons per thermal neutron, which is six to seven times that observed in commercial Ce:Li-glass (GS20). Furthermore, the pulse shape discrimination (PSD) Figure of Merit (FOM) was found to be 2.47, indicating excellent neutron/gamma-ray discrimination capability. This study opens a new avenue for both red/NIR emission and high-light-output neutron scintillators.

DOI： 10.1016/j.mtphys.2025.101997

Open Access

Scopus

出版者・発行元：Japanese Journal of Applied Physics Part 1 Regular Papers and Short Notes and Review Papers  

This study focuses on developing UV-transparent conductive films based on (In<inf>1−x</inf>Al<inf>x</inf>)<inf>2</inf>O<inf>3</inf> for ultraviolet electroluminescent devices. First-principles calculations indicated that compositions with x > 0.6 can achieve a bandgap of ∼5 eV. Thin films fabricated by electron-beam evaporation showed improved transmittance and a blue-shifted absorption edge with increasing Al content. Annealing at 500 °C–550 °C produced films with good crystallinity and high transparency, where In<inf>2</inf>O<inf>3</inf> retained a bixbyite structure and Al<inf>2</inf>O<inf>3</inf> remained amorphous. The resistivity depended on the Al content and the annealing temperature, with a tendency for resistivity to increase at higher temperatures due to the reduction of oxygen vacancies. The film with x = 0.5 annealed at 550 °C exhibited a resistivity of 9.43 × 10⁻⁴ Ω cm, a carrier concentration of 2.05 × 10²⁰ cm⁻³, and a mobility of 32.21 cm² V⁻¹ s⁻¹. The high carrier concentration achieved a resistivity comparable to that of indium tin oxide. These results demonstrate that thin films with high UV transmittance and low resistivity can be obtained even on non-oriented substrates, demonstrating the potential of In–Al–O films as UV-transparent conductive materials.

DOI： 10.35848/1347-4065/ae69ed

Open Access

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Tl⁺-doped Cs3Cu2I5 (Tl:CCI) scintillator is reported to have a light output of 98,200 photons/MeV and energy resolution of 3.3% (FWHM, 662 keV), while the energy resolution is expected to be improved due to high light output compared to other bright scintillators such as Ce:LaBr3 with an FWHM energy resolution of 3.0% at 662 keV and light output of around 60,000 photons/MeV. The energy resolution is related to nonproportional response (NPR), and NPR and energy resolution for Tl:NaI was improved by co-doping with Sr²⁺ and Ca²⁺. Therefore, we grew Tl:CCI and Sr²⁺ co-doped Tl:CCI (Tl,Sr:CCI) crystals by the vertical Bridgman-Stockbarger method to investigate the Sr²⁺ co-doping effect on the scintillation properties. The result shows the NPR was improved with Sr²⁺ co-doping, and the observed energy resolution was improved; Tl:CCI, 0.1 and 0.5% Sr-codoped Tl:CCI had energy resolutions of 4.9±0.1, 4.5±0.1 and 4.3±0.1% (FWHM, 662 keV), respectively. In addition, their intrinsic energy resolutions (FWHM) at 662 keV were estimated to be 2.1±0.2, 1.1±0.2 and 1.0±0.2%, respectively, so that Sr²⁺ co-doping effect for the energy resolution was observed.

DOI： 10.1109/TNS.2025.3649272

Scopus

出版者・発行元：Scientific Reports  

A high-performance Ce³⁺-doped (Gd, Tb)<inf>3</inf>(Ga, Al)<inf>5</inf>O<inf>12</inf> (GTAGG: Ce) single crystal was engineered and characterized, demonstrating a high application potential for advanced X-ray imaging. A transparent 1-inch diameter single crystal was grown using the Czochralski method, demonstrating a significant advancement in large-scale scintillator production. Comprehensive characterization using X-ray diffraction and electron probe micro-analysis confirmed the crystal’s structural integrity. Photoluminescence and radioluminescence spectroscopy demonstrated efficient bidirectional energy transfer between Ce³⁺ and Tb³⁺ ions, a critical mechanism enhancing the performance of the scintillator. X-ray imaging tests were performed using crystals with a thickness of 100 μm at the Aichi Synchrotron Radiation Center. Comparison with the industry-standard LuAG: Ce scintillator showed that the GTAGG: Ce crystal produced 2.4 times higher light output and achieved a high spatial resolution of 0.85 μm. The results indicated that GTAGG: Ce is suitable for the next generation of high-performance X-ray imaging detectors in scientific and medical imaging applications.

DOI： 10.1038/s41598-025-96031-5

Open Access

Scopus

出版者・発行元：Radiation Measurements  

Cross-sectional images were obtained using photon-counting computed tomography (PCCT) for medical applications, incorporating a silicon photomultiplier (SiPM) and Ce-, Mg- and Al-codoped SrHfO<inf>3</inf> transparent-ceramic scintillator (Mg/Al/Ce:SHO). A maximum counting rate of 8 MHz was achieved with our PCCT system equipped with this scintillator. Enhancing the maximum counting rate is crucial for short-time imaging, and further advancements in counting capability are essential for clinical applications. The Mg/Al/Ce:SHO scintillator, which has a shorter decay time (∼20 ns) and higher density (7.6 g/cm³) compared to the Ce:(Y, Gd)<inf>3</inf>(Al, Ga)<inf>5</inf>O<inf>12</inf> scintillator used in earlier PCCT systems, was prepared via spark plasma sintering and integrated into the PCCT. The maximum counting rate was estimated by varying the intensity of incident X-ray photons using an X-ray tube and applying a non-paralyzable dead-time model, yielding approximately 8 MHz–double the photon-counting capability of our previous system. Additionally, static phantom imaging with iodine and gadolinium contrast agents was performed at X-ray tube current of 0.5, 1.0 and 2.0 mA. The image quality remained consistent within the standard deviation of CT values despite increasing the tube current. These findings suggest that the Mg/Al/Ce:SHO scintillator offers superior potential for clinical PCCT applications compared to conventional systems.

DOI： 10.1016/j.radmeas.2025.107456

Scopus

出版者・発行元：ACS Omega  

This study explored the influence of Sc³⁺ ions incorporation on the structural, vibrational, luminescent, and scintillation properties of Pr³⁺-doped Lu<inf>3</inf>(Al, Sc)<inf>2.5</inf>Ga<inf>2.5</inf>O<inf>12</inf> garnet crystals. Addressing the limited research on Sc-admixed and Pr³⁺ doped garnet systems, this work successfully demonstrated the crystallization of garnet crystals from the melt, overcoming the substantial atomic mismatch between Sc and Al while preserving the thermodynamic stability of the garnet phase. Importantly, Sc-admixing enhanced atomic homogeneity and allowed for increased doping concentrations of Pr³⁺ ions, which is crucial for tailoring the functional properties of advanced optical materials. The trap depths ranged from 1.63 eV (deep traps) to 0.22 eV (shallow traps) across all samples, with frequency factors predominantly between 1 × 10⁷ and 1 × 10¹¹ s^-1, consistent with first-order thermoluminescent kinetics. From a materials design perspective, Sc³⁺ ions substitution induced beneficial host lattice disorder, enhancing the emission intensity of 4f¹5d<inf>1</inf>¹ → 4f² interconfigurational and 4f² → 4f² intraconfigurational transitions. This effect highlighted the potential of Sc as a promising substituent for enhancing the luminescence intensity of rare earth elements. Synchrotron radiation experiments provided insights into the impact of Sc on band gap energy and energy transfer efficiency toward Pr³⁺ ions offering new opportunities for engineering scintillators and phosphors with tunable optical properties.

DOI： 10.1021/acsomega.5c01062

Open Access

Scopus

出版者・発行元：Journal of Luminescence  

Optical thermometry is one of the promising methods of detecting temperature under harsh environments. In this study, for the development of a novel optical thermometer, we focused on Eu-doped (Y, Lu, Sc)<inf>2</inf>O<inf>3</inf> and grew single crystals using the micro-pulling-down method. Crystal growth was performed by systematically changing the ratio of Y to Lu, and the crystalline system and space group were identified to be cubic and Ia–3, respectively, by the powder X-ray diffraction analysis. From the photoluminescence emission spectra, the emission peaks attributed to Eu³⁺ ⁵D<inf>0</inf>–⁷F<inf>1</inf> and ⁵D<inf>1</inf>–⁷F<inf>1</inf> transitions were observed. The temperature dependence of these emission peaks was measured and evaluated using the fluorescence intensity ratio method to estimate the performance as the optical thermometer. It was found that Eu-doped (Y, Lu, Sc)<inf>2</inf>O<inf>3</inf> can be used as the optical thermometer in the temperature range from 430 K to 790 K. The relative sensitivity reached a maximum of 0.22 %K⁻¹ at 760 K.

DOI： 10.1016/j.jlumin.2025.121118

Open Access

Scopus

出版者・発行元：Journal of Materials Chemistry C  

In recent decades, optical thermometry has gained significant attention due to its promising properties, such as non-contact measurement, temperature mapping and immunity to electromagnetic interference. It overcomes the limitations of conventional temperature measurement methods and offers additional benefits. However, the widespread adoption of optical thermometry requires an expanded operating temperature range and improved sensitivity. Therefore, in this study, we focused on solid-solution sesquioxides, which are expected not only to enable the growth of single crystals with a cubic structure but also to allow for a wider selection of luminescence centers. We evaluated the applicability of (Lu, Y, Sc)<inf>2</inf>O<inf>3</inf> single crystals doped with Pr³⁺ and Tb³⁺, which exhibit different temperature dependent behaviors, for optical thermometry. The optical temperature sensing properties evaluated using the fluorescence lifetime method revealed a maximal relative sensitivity of 1.53% K⁻¹ in the temperature range of 78-790 K for Pr³⁺, Tb³⁺:(Lu, Y, Sc)<inf>2</inf>O<inf>3</inf>. These results suggest that (Lu, Y, Sc)<inf>2</inf>O<inf>3</inf> co-doped with Pr³⁺ and Tb³⁺ is a promising candidate for optical thermometry.

DOI： 10.1039/d5tc00156k

Open Access

Scopus

出版者・発行元：Crystals  

Ce-doped Lu<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> has a high density, high luminescence efficiency even at high temperatures, and a high effective atomic number, making it a promising candidate for use as a radiation detector in medical devices and resource exploration equipment. In this study, we grow and characterize Pr³⁺ and Ce³⁺-doped Lu<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystals by systematically varying the Ce³⁺ to Pr³⁺ ratio to further improve scintillation properties. The optical characterization results show a bidirectional energy transfer: from the Pr³⁺ 5d levels to the Ce³⁺ 5d levels and from the Ce³⁺ 5d levels to the Pr³⁺ 4f levels. Consistently with this result, the PL decay time of emission from the Pr³⁺ 5d–4f transition tends to become faster as the Ce³⁺/Pr³⁺ ratio increases, due to the energy transfer from the Pr³⁺ 5d levels to the Ce³⁺ 5d levels. Additionally, (Ce<inf>0.0022</inf> Pr<inf>0.0016</inf> Lu<inf>0.9962</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> exhibits a high light yield comparable to Ce-doped Lu<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> and a slightly faster decay time than Ce-doped Lu<inf>2</inf>Si<inf>2</inf>O<inf>7</inf>.

DOI： 10.3390/cryst15030202

Open Access

Scopus

出版者・発行元：Journal of Crystal Growth  

The possibility of growing Cs<inf>1-x</inf>Rb<inf>x</inf>BF<inf>3</inf> (B = Ca, Sr) crystals by micro-pulling-down was investigated due to their potential for application in ultrafast scintillation detectors. A LiF flux was applied to lower the melting point and therefore suppress evaporation of CsF from the melt. Suitable growth conditions were obtained through careful choice of the hot zone elements. A crucible with minimal nozzle length improved mass transport and an afterheater with four windows provided a steep temperature gradient. Inclusion and crack-free crystals of Cs<inf>1-x</inf>Rb<inf>x</inf>CaF<inf>3</inf> (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) and CsCa<inf>1-x</inf>Sr<inf>x</inf>F<inf>3</inf> (x = 0, 0.1, and 0.25) were grown under optimized conditions. Despite the hygroscopic nature of the heavy alkali metal fluorides, all the grown crystals are non-hygroscopic which significantly improves their application potential. Growth of CsCa<inf>1-x</inf>Sr<inf>x</inf>F<inf>3</inf> crystals with higher Sr concentration was complicated by the low solubility of SrF<inf>2</inf> in the LiF-CsF melt and the hygroscopic nature of the CsSrF<inf>3</inf>. The formation of solid solution in the Cs<inf>1-x</inf>Rb<inf>x</inf>CaF<inf>3</inf> and CsCa<inf>1-x</inf>Sr<inf>x</inf>F<inf>3</inf> systems was investigated through the dependence of lattice parameters on nominal composition.

DOI： 10.1016/j.jcrysgro.2024.127919

Scopus

出版者・発行元：Journal of Alloys and Compounds  

The development of scintillators with co-doping mechanisms has received significant attention due to the resulting enhancements in luminescence and scintillation properties. Scintillators such as Ce-doped (Gd,Tb)<inf>3</inf>(Al,Ga)<inf>5</inf>O<inf>12</inf> have been recognized for their improved performance, attributed to the effective energy transfer between Ce³⁺ and Tb³⁺ ions. Nevertheless, the presence of Gd³⁺ introduced complexities, as its absorption lines strongly overlap with those of Tb³⁺, thus masking the details of mechanisms of the Tb³⁺↔Ce³⁺ energy transfer. This study endeavored to elucidate this mechanism by comparing the luminescence characteristics of Ce,Tb co-doped Y<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> (YAGG) and Gd<inf>3</inf>A<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> (GAGG) single crystals. Through detailed photoluminescence spectral analysis, it was discerned that GAGG exhibited a more robust Tb³⁺↔Ce³⁺ energy transfer, as evidenced by a marked extension in the decay time of Ce³⁺ luminescence. Furthermore, GAGG demonstrated superior integrated radioluminescence intensity across all compositions which is a result of efficient energy transfer from Gd³⁺ to the luminescence centers. Additionally, comparative thermally stimulated luminescence glow curves, revealed distinctive spectral features between YAGG and GAGG, underscoring the complexity of their luminescence mechanisms. This comparative study not only augmented our comprehension of the intricate energy transfer processes in Ce, Tb co-doped garnet scintillators but also underscored the potential for tailored scintillator development through strategic ion co-doping.

DOI： 10.1016/j.jallcom.2024.176550

Open Access

Scopus

出版者・発行元：Journal of Luminescence  

Driven by the pursuit of optimizing the luminescent properties of garnet-based single crystals for X-ray imaging applications, this work reports on the successful synthesis and in-depth characterization of GYAGG crystals doped with Ce³⁺ or Tb³⁺ ions, and doubly-doped with both of them. Micro-pulling down synthesis yielded crystals with a single cubic phase confirmed by X-ray diffraction. Photoluminescence (PL) and radioluminescence (RL) measurements on Ce³⁺,Tb³⁺ co-doped GYAGG revealed bidirectional energy transfer processes. Characteristic broadband 5d<inf>1</inf>→4f emission of Ce³⁺ centers peaking at 530 nm and narrow 4f→4f emission lines of Tb³⁺ ions starting from ⁵D<inf>4</inf> level within 480–630 nm were observed. At higher doping levels, cross-relaxation in Tb³⁺ pairs resulted depleted ⁵D<inf>3</inf> state and only the emission from ⁵D<inf>4</inf> one was observed in the spectra. Analysis of PL decay characteristics corroborated the spectral observations, confirming progressively decreasing Ce³⁺ decay time (down to 40 ns at 15 % Tb³⁺) due to enhanced Ce³⁺→Tb³⁺ energy transfer. Similarly, the Tb³⁺ decay time accelerated by more than 60 % after the Ce³⁺ co-doping. Notably, co-doping with 0.5 % Ce³⁺ and 10–15 % Tb³⁺ doubled the luminescence intensity of RL spectra compared to 0.5 % Ce³⁺-doping alone, attributed to the increased density of emitting centers.

DOI： 10.1016/j.jlumin.2024.120663

Scopus

出版者・発行元：Journal of Alloys and Compounds  

This study provided the first in-depth investigation of the effects of large dopant incompatibility (Pr³⁺ and La³⁺ ions) on the small host lattice element (Lu³⁺) in Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (LuAG) single crystal. The growth of such complex crystals from the melt presented many challenges. By engineering the ionic radius ratio of RE- and M-site cations, a single-crystal phase stabilized by configurational entropy was achieved. This investigation elucidated the crystallization behavior of configurationally disordered rare-earth aluminum garnet oxide (Lu<inf>1−x−y</inf>Pr<inf>x</inf>La<inf>y</inf>)<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> from the melt and characterized its functional properties, including microstructural, optical, photoluminescence, and scintillation properties, between 5 and 300 K. Relaxation of the imposed strain energy led to local perturbations and destabilization of the garnet structure. Multielemental EDS mapping, micro-Raman spectroscopy, and thermoluminescence revealed the mechanism by which atomic size mismatch drove a smooth transition from the garnet to the perovskite phase in high entropy garnets. The optical, photoluminescence, and scintillation measurements provided fundamental insights into property changes driven by incompatibility doping. Standard and modified Judd-Ofelt theory analysis of absorption spectra determined the phenomenological Judd-Ofelt parameters Ω<inf>λ</inf> and radiative lifetimes. Atomic size mismatch engineering offers a promising approach to overcoming the limitations of conventional eutectic synthesis methods.

DOI： 10.1016/j.jallcom.2024.174078

Scopus

出版者・発行元：Optical Materials X  

Pr-doped scintillators are attracting attention because of their potential applications in medical devices. In this study, we focused on Pr-doped (La, Y)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillators to grow single crystals by the micro-pulling-down method and to evaluate their optical and scintillation properties. From the powder XRD results, the crystal structure and the space group were identified to be monoclinic and P2<inf>1</inf>/n, respectively. The results of optical and scintillation characterization show that the luminescence from the Pr³⁺ 5d<inf>1</inf>–4f transition increases with increasing Pr³⁺ concentration. The maximum light yield was also obtained for the sample with the highest Pr³⁺ concentration. The Pr-doped (La, Y)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystal shows promising properties for application in radiation detection.

DOI： 10.1016/j.omx.2024.100318

Open Access

Scopus

出版者・発行元：Journal of Crystal Growth  

For the decommissioning of Fukushima Daiichi Nuclear Plants, a novel real-time dose-rate monitor consisting of a scintillator, 100-m long optical fiber and CCD spectrometer has been proposed, and this scintillation material is required to have an emission wavelength of longer than approximately 650 nm. In this paper, as a candidate material for the system, we focused on Ce/Cr co-doped Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (Ce/Cr:GGG) single crystals grown by the micro-pulling down method. Since the light output of this material was expected to depend on the Cr³⁺ concentration, we investigated the relationship between Cr segregation and luminescence properties in Ce/Cr:GGG crystal. Generally, a single photon counting method is not available to evaluate its light output accurately due to the long decay time, we used a novel technique “emission-intensity two-dimensional- mapping method” (2D-image method) to verify the light intensity at each point of the sample. This method realized estimation of the light intensity within the sample, though segregation of Cr³⁺ is observed. The results showed that Cr was concentrated in the center part along the radial direction in the grown crystals, while all parts had an emission wavelength of approximately 730 nm excited by X-ray. Using the 2D-image method, emission intensity was found to correspond to the Cr concentration, and its correlation coefficients between emission intensity and Cr concentration were over 0.8. We found that our material is available for the monitoring system when the Cr dense part of the crystal is cut and used.

DOI： 10.1016/j.jcrysgro.2024.127581

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

The growth of Er-doped La<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> (LHO:Er) single crystals with a high mp of 2413 °C was achieved by the melt-growth method using a tungsten (W) crucible. Polished LHO:Er specimens were obtained from the as-grown crystals. The full width at half maximum of the X-ray Rocking curve on the (222) diffraction peak was 599 arcsec, and the crystals have relatively low crystallinity. The photoluminescence spectra of the polished LHO:Er specimen showed emission peaks originating from the Er³⁺ ions in both the visible and IR wavelength ranges. It also exhibited scintillation light under X-ray irradiation.

DOI： 10.35848/1347-4065/ad1e97

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

A calculation model for predicting the temperature characteristics of the double-layered resonator (DRL) was developed by using the total strain ratio including the influence of the waves reflected at the bonding boundary. The validity of the model proposed was examined from the comparison between the measured and calculated results for a DRL specimen consisting of 129.55°Y- and 0°Y-quartz substrates. The calculation results of the model proposed demonstrated that it is possible to predict the trends of changes in experimental values of temperature characteristics not only in the 1st-order mode but also in the higher-order modes. In addition, the changes in the particle displacement distribution and temperature characteristics of the DLR obtained by the model proposed were also in good agreement with the results of finite element method analysis. The proposed model is expected to greatly contribute to the design of DLRs with high excitation efficiency and excellent temperature characteristics.

DOI： 10.35848/1347-4065/ad1fb1

Scopus

出版者・発行元：Journal of Crystal Growth  

In our search for cross-luminescence (CL) scintillators suitable for fast-timing applications, we have chosen CsMgF<inf>3</inf> as one of the perspective candidates. During the attempts to grow CsMgF<inf>3</inf> by the micro-pulling-down method, we have revealed the presence of Cs<inf>4</inf>Mg<inf>3</inf>F<inf>10</inf> which is in contradiction with the published equilibrium phase diagram. The Cs<inf>4</inf>Mg<inf>3</inf>F<inf>10</inf> has an orthorhombic structure, consisting of face-sharing MgF<inf>6</inf> octahedra triplets (4 triplets per unit cell), joined to 4 other triplets by corner sharing. These chain-like structures are separated by Cs⁺ ions. Moreover, Cs<inf>4</inf>Mg<inf>3</inf>F<inf>10</inf> is non-hygroscopic despite the hygroscopic nature of CsF. The best crystals were grown from CsF-rich melt to suppress off-stoichiometry due to CsF evaporation during crystal growth. Both radioluminescence spectra and scintillation decay kinetics exhibit complex character and the presence of CL in Cs<inf>4</inf>Mg<inf>3</inf>F<inf>10</inf> is still under question. However, due to relatively low scintillation efficiency and the presence of slow components in scintillation decay, Cs<inf>4</inf>Mg<inf>3</inf>F<inf>10</inf> is not suitable for fast-timing applications.

DOI： 10.1016/j.jcrysgro.2024.127568

Scopus

出版者・発行元：Journal of Crystal Growth  

³He gas detectors have been commonly used in applied technology related to thermal neutron detectors; however, owing to the depletion of ³He, applications using solid-state scintillators are expanding. In recent years, our group has reported a novel Tl:CsI/⁶LiBr eutectic scintillator for thermal neutron detection, which has excellent light yield and (n,γ) discrimination ability. In practical applications of eutectic scintillators, achieving eutectic production precisely at the eutectic point is crucial to ensure a high production yield and the development of a uniform eutectic structure. However, the phase diagram of the CsI-LiBr system has not yet been reported. In this study, the phase diagram obtained from calorimetry was investigated. Furthermore, eutectic fabrication was performed at the eutectic point, and the neutron response was evaluated.

DOI： 10.1016/j.jcrysgro.2023.127543

Scopus

出版者・発行元：Journal of Instrumentation  

Real-time dose-rate monitoring system under the high dose-rate situation is required for the decommissioning of Fukushima Daiichi Nuclear Plants to remove the debris remaining inside the plants. We have proposed a dose-rate monitor consisting of a scintillator, over 100-m long optical fiber and CCD spectrometer. Some noises with a dominant emission wavelength of below 550 nm originating from the optical fiber itself must be separated from the signal from the scintillator, and the signal region has been defined as 650–1000 nm to use significant data, up to now. In this paper, we investigated if the noise region defined as below 550 nm can be supporting data for the monitoring system, because such noises are expected to include position information through the fiber. In the emission spectrum, the intensities of the noise emission or absorption band are expected to depend on the position of the fiber, and we demonstrated such dependence, “one-dimensional dose-rate distribution”, with 20 m-long optical fiber and CCD spectrometer. Optical fiber was placed around a ⁶⁰Co source with an activity of approximately 60 TBq, and emission spectra of the fiber were acquired with different dose-rate conditions from 10 to 700 Gy/h. The noise intensities were well fitted with the power function as a function of the product of fiber length and dose rate, and we found that fiber noise has rate information in one-dimensional imaging.

DOI： 10.1088/1748-0221/19/02/C02053

Scopus

出版者・発行元：Journal of Crystal Growth  

Mg<inf>2</inf>Si/Si eutectics are grown from melt by the Vertical Bridgman method using a carbon crucible at three pulling rates. All the Mg<inf>2</inf>Si/Si eutectics are composed of Mg<inf>2</inf>Si and Si phases, and the eutectic structure becomes finer with an increase in the pulling rate. Increasing the pulling rate systematically decreases the thermal conductivities of the Mg<inf>2</inf>Si/Si eutectics, suggesting that a decrease in the thermal conductivity is attributed to an increase in phonon scattering at the boundaries between the two phases. The power factor and figure of merit of the Mg<inf>2</inf>Si/Si eutectics are larger than those of Mg<inf>2</inf>Si above 400 °C because of the increase in the Seebeck coefficient. The figure of merit, ZT, of the Mg<inf>2</inf>Si/Si eutectics solidified at a 10³ mm/min pulling rate reached 0.076 at 600 °C.

DOI： 10.1016/j.jcrysgro.2023.127533

Scopus

出版者・発行元：Crystals  

The ³He gas is commonly used for the detection of thermal neutrons. However, with the depletion of ³He gas, there is a need to develop new solid scintillators for thermal neutron detection. Solid scintillators containing ⁶Li, which have large neutron capture cross-sections and a large amount of energy released by transmutation reactions, are commonly used as alternative candidates. However, only single-crystal scintillators are currently used, and their ⁶Li concentration is limited by their chemical composition. In this study, we designed, grew, and evaluated a new eutectic scintillator, Rb<inf>2</inf>CeCl<inf>5</inf>/LiCl, which can improve the ⁶Li concentration compared with single-crystal scintillators. Rb<inf>2</inf>CeCl<inf>5</inf>, which was selected as the scintillator phase, has excellent scintillator properties (light yield: 36,000 photons/MeV, decay time: mostly 24 ns, slightly 153 ns), and is less deliquescent than other halide scintillators. The crystal grown using the vertical Bridgman method exhibited a eutectic phase composed of Rb<inf>2</inf>CeCl<inf>5</inf> and LiCl. The eutectic crystals exhibited Ce³⁺ 5d-4f emissions, with a peak between 360 and 370 nm. The Rb<inf>2</inf>CeCl<inf>5</inf> phase was identified as the luminescent phase via cathodoluminescence mapping, and 16,000 photons/neutron of the light yield and 56.1 ns of the decay time were observed. This study indicates that the Rb<inf>2</inf>CeCl<inf>5</inf>/LiCl eutectic scintillator is a promising candidate for use in thermal neutron detectors.

DOI： 10.3390/cryst14020154

Open Access

Scopus

出版者・発行元：Nature Materials  

Multiferroic materials, particularly those possessing simultaneous electric and magnetic orders, offer a platform for design technologies and to study modern physics. Despite the substantial progress and evolution of multiferroics, one priority in the field remains to be the discovery of unexplored materials, especially those offering different mechanisms for controlling electric and magnetic orders¹. Here we demonstrate the simultaneous thermal control of electric and magnetic polarizations in quasi-two-dimensional halides (K,Rb)<inf>3</inf>Mn<inf>2</inf>Cl<inf>7</inf>, arising from a polar–antipolar transition, as evidenced using both X-ray and neutron powder diffraction data. Our density functional theory calculations indicate a possible polarization-switching path including a strong coupling between the electric and magnetic orders in our halide materials, suggesting a magnetoelectric coupling and a situation not realized in oxide analogues. We expect our findings to stimulate the exploration of non-oxide multiferroics and magnetoelectrics to open access to alternative mechanisms, beyond conventional electric and magnetic control, for coupling ferroic orders.

DOI： 10.1038/s41563-023-01759-y

Scopus

出版者・発行元：Journal of Alloys and Compounds  

Halide compounds with chemical formula A<inf>2</inf>MX<inf>6</inf> (A: alkali metal or Tl, M: tetravalent metal, X: halogen) have previously been reported as intrinsic scintillators. However, some application fields e.g., utilizing waveguides, require novel scintillators with emission wavelengths longer than that of Cs<inf>2</inf>HfI<inf>6</inf> as bright and red/infrared scintillators. Thus, in this study, cation-substituted Cs<inf>2</inf>HfI<inf>6</inf> crystals (Rb<inf>2</inf>HfI<inf>6</inf>, K<inf>2</inf>HfI<inf>6</inf>, Cs<inf>2</inf>ZrI<inf>6</inf>, Rb<inf>2</inf>ZrI<inf>6</inf>, and K<inf>2</inf>ZrI<inf>6</inf>) were grown using the vertical Bridgman method, and their crystal structures were analyzed via single-crystal X-ray diffraction. The crystal structures of Cs<inf>2</inf>HfI<inf>6</inf> and Cs<inf>2</inf>ZrI<inf>6</inf> were determined to be cubic (space group: Fm3̅m), Rb<inf>2</inf>HfI<inf>6</inf> and Rb<inf>2</inf>ZrI<inf>6</inf> were tetragonal (space group: P4/mnc), and K<inf>2</inf>HfI<inf>6</inf> and K<inf>2</inf>ZrI<inf>6</inf> were monoclinic (space group P2<inf>1</inf>/c). In addition, the emission spectra of Rb<inf>2</inf>HfI<inf>6</inf>, K<inf>2</inf>HfI<inf>6</inf>, Rb<inf>2</inf>ZrI<inf>6</inf>, and K<inf>2</inf>ZrI<inf>6</inf> showed that their peaks exhibited a 25 nm red-shift in comparison with that of Cs<inf>2</inf>HfI<inf>6</inf>, whereas those of Cs<inf>2</inf>ZrI<inf>6</inf> did not. For A<inf>2</inf>MI<inf>6</inf> compounds, the emission was effectively determined by A-site cation substitution. Moreover, the pulse-height spectra were successfully measured for A<inf>2</inf>HfI<inf>6</inf>. The scintillation light outputs of Cs<inf>2</inf>HfI<inf>6</inf>, Rb<inf>2</inf>HfI<inf>6</inf>, and K<inf>2</inf>HfI<inf>6</inf> were estimated to be approximately 60,000, 40,000, and 33,000 photons/MeV, respectively.

DOI： 10.1016/j.jallcom.2023.172506

Scopus

出版者・発行元：Journal of Physics Conference Series  

The luminescence characteristics of Gd3Al2Ga3O12:Ce3+ garnet scintillator crystals codoped with Li+ and Mg2+ ions were investigated. The excitation and emission spectra were obtained within the energy range of 3.6-21.6 eV, at both liquid helium and room temperature conditions to examine the effects of Li+ and Mg2+ codoping on cerium valence states, gadolinium-cerium energy transfer, and defect formation. Codoping with Mg2+ was found to efficiently convert Ce3+ to Ce4+, evidenced by significant changes in the shapes of the excitation spectra profile for Ce3+ luminescence in the exciton range, while Li+ had little impact. The presence of the high concentration of Ce4+ ions hampered the Gd3+→Ce4+ energy transfer. Redshifts in Ce3+ emission peaks indicated codopant-induced perturbations to the crystal field environment. The significant changes in the location of the Ce3+ excitation bands of Ce3+ luminescence in the exciton range further suggested alterations in the elemental distributions by the creation of complex defect clusters, particularly with Mg2+ codoping. The results demonstrate that Li+ and Mg2+ uniquely impact cerium valence, energy transfer processes, and structural properties in GAGG:Ce crystals.

DOI： 10.1088/1742-6596/2712/1/012011

Open Access

Scopus

出版者・発行元：Ceramics International  

Scintillators are used not only as single crystals in radiation detection systems but also as arrays, columns, and fibers. In this study, a novel optical-guiding crystal scintillator (OCS) was fabricated using an Eu:SrI<inf>2</inf> crystal as the core and borosilicate glass as the cladding. The OCS has an elongated shape and can be flexibly processed like an optical fiber. Furthermore, because inorganic scintillator crystals are used as the core, the OCS has high sensitivity to high-energy radiation, such as γ- and X-ray radiation, unlike plastic scintillators. In this study, by observing the cross section of the fabricated OCS, identifying the crystal structure, and investigating the radioluminescence spectrum under X-ray irradiation, OCS fabrication in accordance with the OCS design specifications was confirmed, and the SrI<inf>2</inf> crystal structure and Eu²⁺ 5d–4f luminescence were maintained. The γ-ray responses, such as light yield and decay time, were also investigated.

DOI： 10.1016/j.ceramint.2022.12.264

Scopus

出版者・発行元：Journal of Instrumentation  

Internal exposure for decommissioning workers at the Fukushima Daiichi Nuclear Power Plant must be prevented, and we have developed a monitoring system for alpha-ray emitting dust (alpha dust). When the dust size is less than several tens of micrometers, a dust protection mask does not work effectively to prevent internal exposure. Since no devices have been operated to observe alpha-dust images in real-time up to now, we have developed an alpha-ray imaging detector consisting of a scintillation material and imaging detector. Scintillators are required to have high light output and chemical stability. Cs<inf>3</inf>Cu<inf>2</inf>I<inf>5</inf> (CCI) scintillator was found to be one of the candidates, and an imaging test was operated with this material. The CCI crystal was grown by the Bridgman-Stockberger method, and a scintillation sheet for alpha-ray imaging was prepared by CCI microcrystals with a thickness of approximately 70 μm on a 200-μm thickness transparent polyethylene terephthalate film as a first imaging test. The sheet was irradiated with 5.5-MeV alpha rays from an ²⁴¹Am source, and scintillation photons were detected with a CMOS camera through an optical lens. We succeeded in visualizing alpha rays, and a position resolution of our system achieved approximately 16.2 ± 2.6 μm (10-90 %). This resolution was similar value to other imaging devices with Ag:ZnS powder scintillator, and a CCI single crystal sheet was expected to reach better resolution.

DOI： 10.1088/1748-0221/18/12/C12009

Scopus

出版者・発行元：Applied Physics Express  

Li<inf>2</inf>HfBr<inf>6</inf> with host emission was grown as a gamma-ray- and neutron-sensitive scintillator. Decay time of Li<inf>2</inf>HfBr<inf>6</inf> was estimated to be less than 5 μs, and single-photon counting is available to evaluate its light output. The emission wavelength under X-ray excitation was approximately 570 nm, which is a longer wavelength than that of commonly used neutron scintillators, e.g. Li-glass. The light output excited by thermal neutrons was estimated to be 52000 photons per thermal neutron, which is approximately eight to nine times higher than that of Li-glass. Additionally, neutrons and gamma rays were discriminated using the pulse-shaped discrimination technique for Li<inf>2</inf>HfBr<inf>6</inf>

DOI： 10.35848/1882-0786/ad03ab

Open Access

Scopus

出版者・発行元：Aip Conference Proceedings  

We report on inorganic crystal purification for the search for the neutrinoless double-beta decay of 48Ca using CaF2 crystals. We are working on the purification of CaF2 crystal, which is made from water-insoluble raw materials. The goal of the purity in this crystal is ≤1 μBq/kg. We measured the impurities in the crucible and CaF2 powder before we made a molten product of the CaF2. We will consider the correlation between the purity contained in the materials around the crystal growth and the purity of the molten product. The material-selection policy and prospects for the large-volume detector system will be discussed.

DOI： 10.1063/5.0161258

Scopus

出版者・発行元：Optical Materials  

(La<inf>0.99</inf>Yb<inf>0.01</inf>)<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> (Yb:LaHO) crystal has been developed by the core heating method as a near-infrared-emitting oxide scintillator for a fiber reading remote-dosimetry system under the high-dose-rate region. This system consists of a scintillator, a long silica optical fiber and a detector unit. Near-infrared-emitting photons can be separated from significant fiber-derived noise mainly observed in the UV–blue range. The noise is generated in the optical fiber itself by gamma-rays and charged particles. The Yb:LaHO crystal had a maximum emission peak at 975 nm when excited by X-rays and a transmittance of approximately 29% at 977 nm. The afterglow intensity of the Yb:LaHO crystal under X-rays was 11% that of Cr:α-Al<inf>2</inf>O<inf>3</inf> (ruby) crystal. We demonstrated the applicability of the remote-dosimetry system with the Yb:LaHO crystal irradiated with gamma rays from a ⁶⁰Co source with an activity of ∼77 TBq. The signal-to-noise ratio (SNR) of the Yb:LaHO crystal was 1.9 times higher than that of the ruby crystal at ∼ 1 kGy/h, and the lowest limit of the dynamic range was comparable between the Yb:LaHO and ruby crystals. The results of the SNR and afterglow intensity showed that the Yb:LaHO crystal is a more suitable scintillator than the ruby crystal for fiber reading remote-dosimetry systems.

DOI： 10.1016/j.optmat.2023.113941

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

In this study, Ce:6LiCl/LaCl3 with a high 6Li concentration was developed as a novel thermal neutron scintillator, in which Ce3+ serves as an activator for the LaCl3 phase. The Ce:6LiCl/LaCl3 eutectic was grown in a quartz ampoule (inner diameter: 4.0 mm) using the Bridgman-Stockbarger technique. The grown eutectic contained 0.038 mol/cm36Li, which is greater than that found in commercially available scintillators such as LiCaAlF6 single crystals and Li glass. The Ce:6LiCl/LaCl3 eutectic has a lamellar eutectic structure and is optically transparent. A 350-nm emission due to Ce3+ 4f-5d transition was observed. The light yield under neutron irradiation was estimated to be 5.0 times higher than that of Li glass. In this eutectic, the 6Li ( n , a 3 H reaction made the 6LiCl phase to act as the neutron capture phase and LaCl3 to act as the scintillator phase.

DOI： 10.1109/TNS.2023.3271639

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

In this study, a novel thermal neutron scintillator of Tl:CsI/LiBr was developed. The eutectics were fabricated at various growth rates and investigated their scintillation properties. As a material design guideline, Tl:CsI, which has an excellent ratio, was selected as the scintillator phase to realize high light yield at the energy of rays and tritons generated by the nuclear transmutation reaction with 6Li and LiBr, which has a refractive index close to that of CsI, was selected as the neutron capture phase. Radioluminescence (RL) measurement under X-ray irradiation was also performed to obtain the emission spectrum of the eutectics. The light yield and decay time for thermal neutron were measured using 252Cf and were much higher than those of conventional scintillators for thermal neutron. Furthermore, fabricated eutectic can have the higher sensitivity to thermal neutron due to the high 6Li concentration compared to conventional single-crystal scintillators. Therefore, we have succeeded in developing a promising scintillator material.

DOI： 10.1109/TNS.2023.3278465

Scopus

出版者・発行元：Journal of Materials Chemistry C  

This research investigated the crystal chemical principles related to the incorporation of incompatible atoms into a garnet host lattice. These considerations might be used to guide and drive the design of new garnet compounds with novel properties. The strongly incompatible La atoms at the Lu sites of the Lu<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce host lattice served as a research model. This study showed the possibility of designing material properties by exploiting atom mismatches in a crystal lattice. Lu<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce0.075% crystals with increasing concentrations of La³⁺ ions were grown from the melt using the micro-pulling down method. The concentration of La³⁺ ions above 0.300 at% imposed physical and chemical boundary conditions on the crystallization process. The radial distributions of the chemical elements were studied as a function of the concentration of La³⁺ ions. It was revealed that La³⁺ codoping significantly reduced the cross-sectional fluctuation of the Ga and Al atoms. Persistent green-yellow luminescence due to the inter-configurational 5d → 4f transition of Ce³⁺ was observed after the blue-light excitation. The LuAGG:Ce0.075%,La0.015% phosphor showed long persistent luminescence for more than 14 h above 0.32 mcd m⁻², the detection limit of a human eye. The thermoluminescence glow curves revealed that the addition of La³⁺ ions increased the concentration of traps.

DOI： 10.1039/d3tc01304a

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

In this study, optical-guiding crystal scintillator (OCS) and bundled plates were fabricated. Considering the performance and melting point of halide scintillators and the softening point of glass, Tl:CsI was selected as the fiber core and borosilicate glass as the cladding. Thus, the fabricated OCS had a scintillator in the core and glass in the cladding. The scintillator was remelted and unidirectionally solidified to remove the voids in the OCS and form a single crystal. Consequently, the OCS served as a scintillator fiber with excellent optical-guiding performance and high sensitivity to γ- and X-rays. An OCS plate was also fabricated using bundles of OCSs with diameters of several tens of microns. The developed OCS plate is expected to be a high-resolution and high-sensitivity imaging plate because of its excellent optical-guiding performance.

DOI： 10.35848/1347-4065/acb3d1

Scopus

出版者・発行元：Applied Physics Express  

Scintillation properties of a flexible optical-guiding crystal scintillator with a thallium-doped CsI (Tl:CsI) crystal and borosilicate glass as the core and cladding, respectively, are reported. The as-fabricated optical-guiding crystal scintillator exhibits a light yield of 31,000 photons MeV⁻¹ under 662 keV γ-ray irradiation. The recrystallized sample is transparent and provides a higher light yield of 54,000 photons MeV^-1, which is comparable to that of single-crystal Tl:CsI. The decay times are 400 ns (28%) and 1,350 ns (72%). This material can serve as a scintillator fiber with high sensitivity to γ- and X-rays, high light yield, and energy discrimination.

DOI： 10.35848/1882-0786/acb891

Open Access

Scopus

出版者・発行元：Journal of Materials Chemistry C  

Cerium-doped rare-earth aluminum garnets represent an important class of scintillation and luminescent materials that are widely used in different technical fields, including medical imaging and solid-state white light sources, whose performances have to be further improved. One of the most effective tools for improving the light yield and timing characteristics of these materials is codoping with optically inactive ions. Herein, we investigate the Li⁺ incorporation, as well as defect formation processes imposed by X-ray and UV irradiation, in Li⁺-codoped Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf>:Ce garnet scintillation crystals with the use of electron paramagnetic resonance (EPR), ⁷Li nuclear magnetic resonance, and thermally stimulated luminescence (TSL) methods. The EPR study showed that the Ce³⁺ content in the Li⁺-codoped crystals does not depend visibly on the Li concentration. The EPR spectra of X-ray-irradiated Li⁺-codoped YAG crystals revealed the presence of both isolated O⁻ centers (a hole trapped at the oxygen ion) and O⁻ centers stabilized by the neighboring Li⁺ ions. The latter centers are responsible for the TSL peak at 320 K. Our data also show that at low Li concentrations in the melt, the Li⁺ ions mainly substitute for Y³⁺ ions. However, at high Li⁺ ion concentrations (∼1 at% in melt), the Li⁺ ions also substitute for Al³⁺ ions. A strong increase in the oxygen vacancy concentration in the Li⁺-codoped crystals suggests that oxygen vacancies serve as effective compensators for the negative excess charge introduced into the crystal lattice by Li⁺ ions, thus suppressing the Ce³⁺ → Ce⁴⁺ conversion process, which plays an important role in the acceleration of the scintillation decay. The obtained data suggest that the decrease in a slow component in the scintillation decay of the Li⁺ ion-codoped crystals is caused, at least partly, by the redistribution of trapped charge carriers to more thermally stable centers.

DOI： 10.1039/d2tc04520f

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

A new experimental method to search for T-violating transverse muon polarization (P<inf>T</inf>) in the K⁺→π⁰μ⁺ν (K<inf>μ3</inf>) decay using a segmented CeF<inf>3</inf> calorimeter has been proposed. One of the key issues for this experiment is the choice of a scintillation material which can maintain the μ⁺ spin polarization for several μ⁺ lifetimes. The residual μ⁺ polarization in a CeF<inf>3</inf> scintillating crystal was previously measured at the J-PARC Material and Life Science Facility (MLF). Unfortunately, due to the small size of the CeF<inf>3</inf> material, beam backgrounds contributed significantly to the μSR spectra, and the absolute μ⁺ polarization could not be determined accurately. In order to solve this problem, a new experiment was performed at the MLF using a large CeF<inf>3</inf> crystal, which successfully reduced the beam backgrounds to a negligible level. The residual μ⁺ polarization in CeF<inf>3</inf> was measured by changing the strength of the applied longitudinal field (LF). The polarization was obtained to be 90 ± 2% with LF = 140 Gauss, which is high enough to perform the new T-violation experiment.

DOI： 10.1016/j.nima.2022.166932

Scopus

出版者・発行元：Optical Materials X  

In this study, Tl:CsI/CsCl/KCl ternary eutectic scintillators were grown using the vertical Bridgman–Stockbarger method by unidirectional solidification. The CsI and KCl phases were elongated along the growth direction, based on backscattered electron imaging (BEI) observations. The Tl:CsI scintillator phase grew as a matrix, which can be used to create optical waveguides for scintillation light. The expected Tl⁺ emission peak was observed at 550 nm under X-ray excitation. This emission was attributed to the self-trapped excitons perturbed by TI⁺ in Tl:CsI. The decay time of the Tl:CsI/CsCl/KCl eutectic was 285 ns, and its light output was estimated to be 10,800 photons/MeV.

DOI： 10.1016/j.omx.2022.100159

Open Access

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

The influence of the reflected waves at the bonding boundary on the resonance waveform and temperature characteristics was investigated using α-quartz (QZ). The double-layered resonator specimen was fabricated using 129.55°Y-and 0°Y-cut QZ substrates with the thickness ratio x = 0.520. The temperature characteristic of the 1st and 2nd resonance modes at the range from 100 °C to 300 °C was deviated from the calculated values estimated by the equations considering thickness ratio and electric flux density ratio proposed in the previous work. Considering the phase matching conditions, it was clarified that the reflected waves at the bonding boundary are in phase in the lower acoustic impedance substrate and out of phase in the other substrate for the 1st mode, so the temperature characteristics are mainly dominated by that of the lower acoustic impedance substrate. In contrast, these relationships are reversed for the 2nd mode.

DOI： 10.35848/1347-4065/ac4a03

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

A 6LiBr/CeBr3 eutectic thermal-neutron scintillator, with a high 6Li concentration, was developed using the vertical Bridgman method. The grown eutectic contained an 6Li molar ratio of 35%, which is higher than those of the commercial neutron scintillators such as Ce:LiCaAlF6 and Ce:Cs2LiYCl6. Furthermore, it showed optical transparency and a lamellar eutectic structure elongating along the growth direction. The synthesized eutectic showed emission peaks at 360 and 380 nm, originating from the Ce3+ 5d-4f transition in the CeBr3 scintillation phase. The scintillation performance of 6LiBr/CeBr3 was evaluated under X-ray, γ-ray, and neutron irradiation to corroborate its neutron detection potential.

DOI： 10.35848/1347-4065/ac4076

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

In this study, a large-size eutectic scintillator of Tb-doped BaCl2/NaCl/KCl was grown using the Czochralski (Cz) and halide vertical Bridgman methods (H-VB). The suitability of these two growth methods for growing the eutectic was compared. Finally, 1 inch diameter eutectic bulks were obtained using the H-VB method. The Tb3+-derived strongest intensity peak at approximately 550 nm was observed by X-ray irradiation. An approximately 3 × 3 mm transparent eutectic wafer was cut and polished from the grown eutectic bulk. An imaging test using α-ray was performed using the grown eutectic, a fiber optic plate, and an electron-multiplying CCD camera. The resolution performance for radiation-imaging applications was evaluated.

DOI： 10.35848/1347-4065/ac3b23

Scopus

出版者・発行元：Optical Materials X  

In this study, it was demonstrated that Zn<inf>3</inf>Ta<inf>2</inf>O<inf>8</inf> crystals containing zinc oxide with high vapor pressure can grow in melt by the shielded arc melting method. The radiation response characteristics of the crystals were evaluated. The grown crystals showed an emission peak at 410 nm, ascribed to self-trapped excitation, Ta⁴⁺–O²⁻. The full width at half maximum of the X-ray rocking curve was 655 arcsec. The light output under 662 keV gamma-ray irradiation of Zn<inf>3</inf>Ta<inf>2</inf>O<inf>8</inf> was approximately 4,700 photons/MeV. The decay time was 17.3 μs? Thus, the shielded arc melting method was shown to be a quick and economic growth technique for the survey of new scintillator materials containing high-vapor-pressure starting components.

DOI： 10.1016/j.omx.2022.100149

Open Access

Scopus

出版者・発行元：Journal of Crystal Growth  

Ce-doped LaCl<inf>3</inf>/AECl<inf>2</inf> (AE = Mg, Ca, Sr) system eutectics were explored. Ce-doped LaCl<inf>3</inf>/ AECl<inf>2</inf> (AE = Mg, Ca, Sr) eutectics were grown using the Bridgman–Stockbarger method in quartz ampoules. In the case of AE = Mg, Ca, eutectics with submicron-diameter phase-separated scintillator fibers (PSSFs) structure were observed. In the case of AE = Sr sample, a solid solution of La<inf>0.708</inf>Sr<inf>0.292</inf>Cl<inf>2.708</inf> was observed. The plate sample from the grown eutectics has some transparency. The grown eutectic structure showed a mixture of rods and plates shape. This mixed structure was aligned with a length of around 100–400 μm. The Ce:LaCl<inf>3</inf>/CaCl<inf>2</inf> eutectic showed 345 nm emission ascribed to Ce³⁺ 4f-5d transition under X-ray excitation. The Ce:LaCl<inf>3</inf>/CaCl<inf>2</inf> sample resulted in the highest light output of 9,000 photon/MeV, which is comparable to the previously reported eutectic scintillator Ce:GdAlO<inf>3</inf>/α-Al<inf>2</inf>O<inf>3</inf>, 9500 photon/MeV. Scintillation decay time of the Ce:LaCl<inf>3</inf>/CaCl<inf>2</inf> sample under 662 keV gamma-ray excitation was 26.8 ns (26%) and 282 ns (74%).

DOI： 10.1016/j.jcrysgro.2022.126549

Scopus

出版者・発行元：Journal of Alloys and Compounds  

The undoped, Mg²⁺ doped, Ce³⁺ doped as well as Mg²⁺:Ce³⁺ codoped Gd<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> crystals were grown from the melt by the micro-pulling down method. Ce³⁺ and Mg²⁺ ions were codoped in a wide concentration range. A study of Mg²⁺ ion concentration effect on the luminescence and scintillation properties as well as segregation of atoms and defects creation processes were carried out. Mg²⁺ doping in Gd<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> led to the creation of O<inf>O</inf>^• defects localized next to Mg²⁺ sites due to charge imbalance compensation. Consequently, neutral (Mg<inf>Ga/Al/Gd</inf>O<inf>O</inf>)^x defects were formed. In Ce³⁺ doped crystals, Mg²⁺ codoping changed the valence state from Ce³⁺ to Ce⁴⁺ to maintain charge neutrality. Hence, additional neutral (Ce<inf>Gd</inf>^•-Mg<inf>Ga/Al/Gd</inf>′)^x and (Ce<inf>Gd</inf>-Mg<inf>Ga/Al/Gd</inf>O<inf>O</inf>)^x defects appeared. Moreover, Mg²⁺ induced charge imbalance in GAGG crystal might also be compensated by the formation of oxygen vacancies (V<inf>O</inf>^••). The Mg²⁺ ions imposed defects deteriorated the segregation of atoms. Accordingly the radial inhomogeneity of the crystals was diminished. The presence of stable Ce⁴⁺ and defects imposed by Mg²⁺ ions codoping were proved by absorption, photoluminescence, and scintillation decay time analysis. Hence, Mg²⁺ codoping resulted in quenching of the Ce³⁺ luminescence, acceleration of scintillation response, reduction of light yield, and thermally stimulated luminescence. The mechanism explaining a strong luminescence quenching with increasing Mg²⁺ ions concentration was proposed.

DOI： 10.1016/j.jallcom.2022.164154

Scopus

出版者・発行元：Journal of Crystal Growth  

La<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> crystals with a melting point of ∼2418 °C were grown by the micro-pulling-down method using a W crucible and deoxygenated ZrO<inf>2</inf> insulators. A La<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> crystal grown at a rate of 0.07 mm/min (LHO[0.07 mm/min]) showed a high transparency without any visible cracks and inclusions, while a La<inf>2</inf>Hf<inf>2</inf>O<inf>7</inf> crystal grown at a rate of 2.00 mm/min had some cracks. The LHO[0.07 mm/min] crystal had a transmittance of over 70% in the wavelength range of 450–800 nm. The X-ray rocking curve of the LHO[0.07 mm/min] crystal showed a symmetric sharp peak with a full width at half maximum of 138 arcsec. The Laue image revealed that the grown crystals were single crystals.

DOI： 10.1016/j.jcrysgro.2022.126547

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

In this study, Ce:⁶LiBr/LaBr<inf>3</inf> eutectic with a high Li concentration was developed as a novel thermal neutron scintillator. Ce served as an activator for the LaBr<inf>3</inf> phase, and Ce:⁶LiBr/LaBr<inf>3</inf> eutectics were grown via the vertical Bridgman method in quartz ampoules (inner diameter = 4 mm). In the eutectic, the ⁶LiBr phase worked as the neutron capture phase by the ⁶Li (n, a) ³H reaction, and Ce:LaBr<inf>3</inf> worked as the scintillator phase. The Ce:⁶LiBr/LaBr<inf>3</inf> eutectic exhibited a lamellar eutectic structure and optical transparency, as well as 350 and 380 nm emission due to Ce³⁺ 5d-4f transition. The light yield under neutrons excitation was estimated to be 74000 photons/neutron. The scintillation decay time was 18.7 ns.

DOI： 10.1016/j.nima.2022.166384

Scopus

出版者・発行元：Journal of Crystal Growth  

Phenanthrene crystals were grown by the self-seeding vertical Bridgman technique as a neutron scintillation material and their luminescence properties were evaluated. As-grown crystals had no secondary phases from the results of the powder X-ray Diffraction and Fourier transform infrared spectrometer measurements. The radioluminescence emission spectrum had a peak at 408 nm and its profile was similar to that of the photoluminescence emission spectrum. The relative light yield under 5.5-MeV alpha-ray was 1.15 times higher than that of lithium glass GS-20. The light yield of phenanthrene under 662 keV gamma-ray is estimated to be 38 ± 2% of NaI:Tl. The scintillation decay time under neutron excitation was estimated to be 7.30 ± 0.14 ns.

DOI： 10.1016/j.jcrysgro.2021.126494

Scopus

出版者・発行元：Journal of Crystal Growth  

In this study, Tb:BaCl<inf>2</inf> and NaCl/KCl ternary eutectics were grown using quartz ampoules via the vertical Bridgman–Stockbarger method. Each crystal phase had a polygonal columnar shape with a length of 300 µm along the growth direction. The Tb:BaCl<inf>2</inf> scintillator phase grew in the columnar phase. The BaCl<inf>2</inf> scintillator phase is expected to make optical waveguides of the scintillation light. The expected Tb³⁺ emission peak was observed at approximately 360–630 nm under X-ray irradiation. This emission is mainly attributed to the Tb³⁺⁵D<inf>4</inf>→⁷F<inf>6</inf>, ⁷F<inf>6</inf>, ⁷F<inf>5</inf>, ⁷F<inf>4</inf>, and ⁷F<inf>3</inf> transitions and BaCl<inf>2</inf> host emission transition. The photoluminescence decay times of the Tb:BaCl<inf>2</inf>/NaCl/KCl eutectics was 0.49 ms (7.5%) and 6.64 ms (92.5%).

DOI： 10.1016/j.jcrysgro.2021.126467

Scopus

出版者・発行元：IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control  

The effect of the difference in the thickness ratio of the double-layered thickness-shear resonator on the temperature characteristics of the resonance frequency was investigated using a Ca₃TaGa₃Si₂O₁₄ (CTGS) single crystal. Three specimens with thickness ratios of <inline-formula> <tex-math notation="LaTeX">${x} =0.25$ </tex-math></inline-formula>, 0.33, and 0.50 were prepared using <inline-formula> <tex-math notation="LaTeX">$122^{\circ } ~{Y}$ </tex-math></inline-formula>- and <inline-formula> <tex-math notation="LaTeX">$171^{\circ }~{Y}$ </tex-math></inline-formula>-cut CTGS substrates. For the specimens with <inline-formula> <tex-math notation="LaTeX">${x} =0.25$ </tex-math></inline-formula> and 0.33, the temperature characteristics varied depending on the order of the resonance mode. For the specimen with <inline-formula> <tex-math notation="LaTeX">${x} =0.50$ </tex-math></inline-formula>, on the other hand, almost the same temperature characteristics were observed regardless of the order of the resonance mode. To interpret this phenomenon, a new equation for predicting the temperature characteristics of the fundamental mode (first mode) for the double-layered resonator was created using the electric flux density ratio generated in the two substrates. The expected values using this equation were in good agreement with the result of the first mode temperature characteristics.

DOI： 10.1109/TUFFC.2021.3121782

Scopus

出版者・発行元：Journal of Crystal Growth  

La<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf> crystals with a melting point of 2283 °C are grown via the micro-pulling-down (μ-PD) method using Mo and W crucibles to expand the possibility of material research of functional single crystals with high melting points by the μ-PD method. La<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf> crystals grown using Mo and W crucibles under an Ar + 3% H<inf>2</inf> atmosphere are composed of a La<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf> main phase, which includes Mo and W. However, a La<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf> crystal without W can be grown under an Ar atmosphere using the μ-PD method using a W crucible and deoxygenated ZrO<inf>2</inf> insulators. After post-annealing in air at 1000 °C, the La<inf>2</inf>Zr<inf>2</inf>O<inf>7</inf> crystal without W becomes colorless and transparent, indicating a transmittance exceeding 70% in wavelengths ranging from 450 to 800 nm.

DOI： 10.1016/j.jcrysgro.2021.126357

Scopus

出版者・発行元：Scientific Reports  

The internal exposure of workers who inhale plutonium dioxide particles in nuclear facilities is a crucial matter for human protection from radiation. To determine the activity median aerodynamic diameter values at the working sites of nuclear facilities in real time, we developed a high-resolution alpha imager using a ZnS(Ag) scintillator sheet, an optical microscope, and an electron-multiplying charge-coupled device camera. Then, we designed and applied a setup to measure a plutonium dioxide particle and identify the locations of the individual alpha particles in real time. Employing a Gaussian fitting, we evaluated the average spatial resolution of the multiple alpha particles was evaluated to be 16.2 ± 2.2 μmFWHM with a zoom range of 5 ×. Also, the spatial resolution for the plutonium dioxide particle was 302.7 ± 4.6 µmFWHM due to the distance between the plutonium dioxide particle and the ZnS(Ag) scintillator. The influence of beta particles was negligible, and alpha particles were discernible in the alpha–beta particle contamination. The equivalent volume diameter of the plutonium dioxide particle was calculated from the measured count rate. These results indicate that the developed alpha imager is effective in the plutonium dioxide particle measurements at the working sites of nuclear facilities for internal exposure dose evaluation.

DOI： 10.1038/s41598-021-84515-z

Open Access

Scopus

出版者・発行元：Journal of Crystal Growth  

In this study, Tl:CsI/KI/KCl eutectic scintillators were grown using the Bridgman–Stockbarger method by unidirectional solidification. The eutectic phases were uniformly distributed in the transverse direction and were slightly aligned along the growth direction. The Tl:CsI scintillator phase was grown as a matrix, which was then used for creating optical waveguides of the scintillation light. The expected Tl⁺ emission peak was observed at 486 nm under X-ray excitation and cathodoluminescence; this was attributed to the self-trapped exciton perturbed by TI⁺ in Tl:CsI. The decay time of the Tl:CsI/KI/KCl eutectic was 313 ns, and its light output was estimated to be 22,000 photons/MeV.

DOI： 10.1016/j.jcrysgro.2021.126287

Scopus

出版者・発行元：Optical Materials  

Luminescence and scintillation characteristics of Mg²⁺-codoped (Lu<inf>x</inf>Gd<inf>3-x</inf>)Al<inf>2.4</inf>Ga<inf>2.6</inf>O<inf>12</inf>:Ce (x = 0.2–0.8) garnet crystals grown by the micro-pulling down method are investigated. The Ce³⁺ 5d<inf>1</inf> → 4f luminescence is blue-shifted with increasing Lu content due to the decrease in crystal field splitting of the 5 d levels. With increasing Lu content, the shortening of scintillation decay time accompanied with a decrease of LY value as measured at room temperature can be explained by thermal ionization of the Ce³⁺ 5d<inf>1</inf> excited state. Co-doping with Mg²⁺ results in the shortening of scintillation decay time, the reduction of LY value and afterglow intensity. At low temperature the radioluminescence quenching is observed in correlation with large thermoluminescence peaks, which can be attributed to the localization of electrons at intrinsic shallow traps.

DOI： 10.1016/j.optmat.2021.111595

Scopus

出版者・発行元：Journal of Crystal Growth  

We have grown Ce-doped (La,Y)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystal by micro-pulling-down method and investigated its optical and scintillation properties. We have successfully prepared the single crystal with (Ce<inf>0.015</inf>La<inf>0.600</inf>Y<inf>0.385</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> composition. The observed thermal quenching process could be characterized by the quenching temperature (T<inf>50%</inf>) of 526 K and its activation energy was determined to be 0.62 eV. Further considering the thermal quenching factors, it was found that the thermal quenching was caused by at least the thermal ionization and maybe also by classical thermal quenching. The light output and scintillation decay time were evaluated to be ~12,000 photons/MeV and ~42 ns, respectively. These results indicate that (Ce<inf>0.015</inf>La<inf>0.600</inf>Y<inf>0.385</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> has a great potential for application in scintillation materials.

DOI： 10.1016/j.jcrysgro.2021.126252

Scopus

出版者・発行元：Journal of Instrumentation  

GAGG(Ce) is a novel scintillator with a fast response and high light output without a hygroscopic nature. It is expected to be a useful detector for charged particles at high-counting rates. However, the response of the GAGG(Ce) scintillator to charged particles has not been fully examined. In the present work, the light output and energy resolution of the GAGG(Ce) scintillator were measured for protons and alpha particles at E p=5-68 MeV and E α=8-54 MeV as well as gamma rays at E γ=662 keV from a 137Cs source. The results were compared with those of the CsI(Tl) scintillator. The scintillation efficiencies dL/dE of the GAGG(Ce) and CsI(Tl) scintillators were obtained and parametrized as a function of linear energy transfer dE/dx.

DOI： 10.1088/1748-0221/16/10/P10012

Scopus

出版者・発行元：Journal of Luminescence  

This research dealt with the investigation of luminescence properties of undoped and La doped Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> single crystals using synchrotron radiation excitation. The influence of La³⁺ doping on the exciton emission and decay kinetics properties of Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> single crystals was studied at 7 K and room temperature. Undoped and La³⁺ doped samples showed bright luminescence in the UV spectral range. In undoped Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystal, the UV luminescence was associated with Lu<inf>Al</inf> antisite defects, which acted as luminescence centers in the band peaked at 295 nm La³⁺ doping in Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystals caused the formation of La<inf>Lu</inf> luminescence centers and increased the concentration of Lu<inf>Al</inf> antisite defects. Therefore, the luminescence of La doped Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystals was a superposition of the emission coming from both La<inf>Lu</inf> and Lu<inf>Al</inf> centers. Furthermore, La³⁺ doping significantly enhanced the intensity and shifted the UV luminescence of Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystals towards higher energy due to the dominant contribution of La<inf>Lu</inf> luminescent centers in the band peaked at 275 nm. The decay time of heavily La³⁺ doped LuAG crystals was also significantly accelerated due to the prevailing luminescence of La<inf>Lu</inf> centers.

DOI： 10.1016/j.jlumin.2021.118013

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

Optimum measurement condition of the V(x) method proposed as a fast scanning technique of the line-focus-beam ultrasonic material characterization system was theoretically investigated to realize more accurate measurement. Through numerical calculation, it was clarified that the appropriate defocus position z m with higher sensitivity used in the V(x) measurement depended on the waveform attenuation of V(z) curves. It was also clarified that the measurement error caused by the focal distance change due to temperature change in the water coupler could be reduced by choosing the lower defocus position as z m. A method for measuring the surface profile of the specimen by applying the V(x) method with z m > 0 was proposed in order to correct measurement error due to warpage of specimen surface.

DOI： 10.35848/1347-4065/ac06dc

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

Wafers of Tb-doped GdAlO<inf>3</inf>/α-Al<inf>2</inf>O<inf>3</inf> eutectic were fabricated by the micro-pulling-down method using an Ir crucible with a 25 × 25 mm² die. A prototype X-ray phase imaging detector was developed using a CMOS sensor with a fiber optic plate and the eutectic wafer. X-ray spots with an 8.24 μm period were observed using the detector. X-ray phase imaging of a nylon ball with a diameter of 4 mm was also carried out. It was observed that a phase change of approximately 2 μm occurs at the air-nylon interface. This technique of X-ray phase imaging can be realized in the absence of an absorption grating.

DOI： 10.35848/1347-4065/abd708

Scopus

出版者・発行元：Journal of Alloys and Compounds  

We report the absorption and emission properties of neodymium (Nd³⁺)-doped APLF glasses [20Al(PO<inf>3</inf>)<inf>3</inf>-80LiF + x NdF<inf>3</inf>, x = 0.5–2.0 mol%] as potential vacuum ultraviolet (VUV) scintillator materials due to their interconfigurational 4f²5d transitions which have not yet been investigated. The Nd³⁺-doped APLF glasses exhibit absorption and emission peaks from the VUV to the near-infrared (NIR) regions which correspond to the different interconfigurational 4f²5d and intraconfigurational 4f³ transitions of Nd³⁺ ions. Detailed analysis of the absorption and emission spectra reveals that the Nd³⁺-doped glass has a disordered structure and low symmetry, as expected from amorphous materials. However, the most important feature of these glasses is their electric-dipole allowed 4f²5d → 4f³ (⁴I<inf>9/2</inf>) broadband emissions, between two configurations of opposite parity, around 187 nm (VUV) whose ~ 5.0 ns decay times are faster than known Nd³⁺-doped scintillators. At room temperature (RT), the absorption edge located around 192 nm overlaps with this VUV emission indicating that self-absorption primarily limits the emission intensity. This overlap could potentially be minimized by working at low temperatures and doping with higher (>2.0 mol%) concentrations. Despite the presence of self-absorption, the fast emission decay times from the 4f²5d excited state make the Nd³⁺-doped APLF glasses promising new VUV scintillator materials for high-counting-rate fast neutron detection.

DOI： 10.1016/j.jallcom.2020.158096

Scopus

出版者・発行元：Crystal Growth and Design  

We propose a novel crystal growth method, "Core Heating (CH) Method", which is suitable for a search of novel materials with extremely high melting points above the melting (softening) point of an Ir crucible. As a feasibility test of the novel CH method, we fabricated the conventional material, (Y0.99Ce0.01)3Al5O12 (Ce:YAG), with a melting point of ∼1970 °C, because this material can be grown by the conventional melt growth technique like the micropulling down (μ-PD) method for the comparison. We compared scintillation properties for Ce:YAG prepared by the CH and μ-PD methods in order to find if the CH method can be applied to the material search. The crystals grown by both methods showed the YAG single-phase, and almost all their optical and scintillation properties of them were comparable for both samples. Particularly, the light output of Ce:YAG crystal grown by the CH method (20,000 ± 1,000 photons/MeV) was similar to that of the sample grown by the μ-PD method (23,000 ± 1,000 photons/MeV). Therefore, we concluded that the CH method is a useful technique for the search of scintillation materials with extremely high melting points.

DOI： 10.1021/acs.cgd.0c01396

Scopus

出版者・発行元：Applied Physics Express  

Tube shape-controlled Ce-doped Y3Al5O12 (tube-Ce:YAG) single-crystal scintillators were directly grown from a melt via the micro-pulling-down method using a specially-designed iridium crucible. Back-scattering Laue images and X-ray diffraction measurements revealed the tube-Ce:YAG was a single crystal with the YAG phase. Ce distribution in the tangential direction of the tube-Ce:YAG specimen showed that Ce concentrations around the capillary positions were lower than at the corners. This was caused by the small Ce segregation coefficient in the YAG single crystal and from the small convection in the meniscus. The scintillation properties of tube-Ce:YAG specimens were comparable with previously reported Ce:YAG single crystals.

DOI： 10.35848/1882-0786/abc8ab

Scopus

出版者・発行元：Physica Status Solidi Rapid Research Letters  

This research deals with a novel approach for the self-flux growth of Tb<inf>3</inf>Al<inf>5</inf>O<inf>12</inf>:Ce single crystal using the micro-pulling-down method. The self-flux method enables the fabrication of the crystals with excellent photoconversion and scintillation properties. Tb<inf>3</inf>Al<inf>5</inf>O<inf>12</inf>:Ce (TbAG:Ce) efficiently converts the blue light-emitting diode (LED) radiation into bright white light. The gradual change of crystal thicknesses (0.2–1 mm) allows for tuning white light temperature from cold to neutral white. The scintillation response is comparable with that of a high-quality single crystalline film counterpart with a light yield value of around 4500 photons MeV⁻¹ under α particle excitation from 239 Pu radioisotope. This is the highest value obtained for the TbAG:Ce crystal yet.

DOI： 10.1002/pssr.202000327

Scopus

出版者・発行元：Optical Materials  

The scintillators with Ce luminescent centers are widely used for radiation detection. In this study, we focused on the Ce<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> pyrosilicate scintillator and evaluated its optical and scintillation properties. From the result of the temperature dependence of quantum yield of Ce<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> under excitation into the Ce³⁺ 4f-5d<inf>1</inf> transition, it was revealed that at 300°C the Ce<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> had a quantum yield of approximately 40% of that at the room. In addition, Ce<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> had a light output of 9,400 ± 800 photons/MeV and fast decay time (~34 ns) at room temperature, and therefore, it has potential for application in radiation detection.

DOI： 10.1016/j.optmat.2020.110210

Scopus

出版者・発行元：Materials Science and Engineering B  

The growth process, crystal composition, optical and scintillation properties of Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf>:La (La = 0–0.45%) single crystals were investigated in detail. The thermodynamical stability of the garnet phase formation was studied in the undoped and La doped Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> single crystals. The crystals were grown from the melt using a micro-pulling down method. Detailed composition analysis reviled the complex multiphase character of the samples. Both garnet and α-Al<inf>2</inf>O<inf>3</inf> phases were detected in the undoped and slightly La-doped samples, while heavily La-doped crystals contained the mixture of α-Al<inf>2</inf>O<inf>3</inf>, garnet and perovskites phases. The substitution La for Lu led to the formation of La<inf>Lu</inf> centers and increased the concentration of Lu<inf>Al</inf> antisite defects. Both types of centers caused a strong luminescence in the deep UV spectral range. Heavy La-doping significantly enhanced the scintillation performance of Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystals.

DOI： 10.1016/j.mseb.2020.114677

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

The scintillation characteristics of Lu0.8Gd2.2 (Al5-xGax)O12:Ce,Mg ( $x = 2.6$ and 3) single crystals grown by the micropulling down method are investigated. The light yield of 27600 photons/MeV obtained for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg is higher than that of 25 400 photons/MeV obtained for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. The photoluminescence and scintillation decays measured at room temperature (RT) for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg are faster than those for Lu0.8Gd2.2Al2.4Ga2.6O12:Ce,Mg. Temperature dependence of radioluminescence (RL) intensity indicates a lower quenching temperature for Lu0.8Gd2.2Al2Ga3O12:Ce,Mg. Coincidence time resolution of a Lu0.8Gd2.2Al2Ga3O12:Ce,Mg detector in coincidence experiment with a BaF2 detector was measured to be 410 ps. The afterglow and thermally stimulated luminescence (TSL) characteristics below RT are also measured.

DOI： 10.1109/TNS.2020.3005410

Scopus

出版者・発行元：IEEE International Ultrasonics Symposium Ius  

The factor dictating the temperature characteristic of the double layered thickness-shear resonator was investigated by evaluating the resonators with different thickness ratios. Using Ca3TaGa3Si2O14[CTGS], one of the Langasite-type piezoelectric single crystal, double layered resonators with thickness ratios x = 0.25 and 0.5 were fabricated and the temperature dependence of their resonance frequency were measured at -30 to 80°C. As a result, the temperature characteristics for the resonator with x = 0.25 exhibited different profiles depending on the order of resonance mode, on the other hand, those for the resonator with x = 0.5 exhibited no difference among all of the order. Comparing these results with the wave propagation model in the resonator, it was found that the thickness ratio of two layers at the region effectively contributing to the electric field output was deeply related to the deviation of the temperature characteristics.

DOI： 10.1109/IUS46767.2020.9251706

Scopus

出版者・発行元：IEEE International Ultrasonics Symposium Ius  

A new method for measuring material homogeneity using fast scanning technique was proposed and demonstrated with the line-focus-beam ultrasonic-material-characterization (LFB-UMC) system. Similar velocity profiles of leaky surface acoustic wave (LSAW) for a Ca3Ta(Ga0.75Al0.25)3Si2O14[CTGAS] single crystal specimen were successfully obtained by both of the new V(x) and the conventional V(z) methods. We have verified the new V(x) method was 56 times faster than the conventional V(z) method. Although the V(z) method is superior to the V(x) method in a viewpoint of measurement accuracy, the V(x) method has great advantage enabling us to quickly evaluate material homogeneity over the wide area of specimen.

DOI： 10.1109/IUS46767.2020.9251779

Scopus

出版者・発行元：Physica Status Solidi B Basic Research  

Eu-doped CaF<inf>2</inf> is studied for use as a scintillator. Herein, the 3D spatial distribution of Eu ions doped in CaF<inf>2</inf> crystal is evaluated. It is confirmed that both divalent and trivalent Eu ions are doped in CaF<inf>2</inf> crystals from the luminescence spectra of the Eu-doped CaF<inf>2</inf> crystals. Using bandpass filter, the 3D spatial distribution of divalent and trivalent Eu ions is measured, respectively. The 3D spatial distribution of divalent Eu ions with ionic radius larger than that of Ca site is nonuniform with mesh-like pattern. In contrast, the 3D spatial distribution of trivalent Eu ions with ionic radius smaller than that of Ca site is uniform. In Eu-doped CaF<inf>2</inf> crystals grown by micropulling down method, strain caused by the difference in lattice constants between CaF<inf>2</inf> and a seed crystal is confirmed.

DOI： 10.1002/pssb.201900477

Scopus

出版者・発行元：Physica Status Solidi B Basic Research  

Li⁺ codoping of Gd<inf>3</inf>(Ga, Al)<inf>5</inf>O<inf>12</inf>:Ce (GGAG:Ce) single crystals induces the acceleration of scintillation decay time. However, its effect on the scintillation properties of GGAG:Ce remains poorly understood. Herein, the relationship between Ce/Li concentration and scintillation properties is investigated. GGAG crystals with a range of Ce and Li concentrations are grown by the Czochralski method and the scintillation decay and light output of GGAG:Ce, Li are measured. The results show comparable or improved performance compared with conventional scintillators. In optical absorption and photoluminescence (PL) measurements, the conversion of the stable Ce³⁺ to Ce⁴⁺ is not observed in a clear manner in GGAG:Ce samples with variable Li concentration. Instead, some defect-related absorption seems to appear. Temperature dependence of PL decay for samples with variable Ce concentration is also evaluated. A shift of the luminescence quenching temperature is observed for GGAG samples with >0.2% Ce.

DOI： 10.1002/pssb.201900504

Scopus

出版者・発行元：Optical Materials  

Single crystal of the mixed-halogen compound Cs<inf>2</inf>HfCl<inf>3</inf>Br<inf>3</inf> was grown by the vertical Bridgman method, and we investigated its crystal structure and optical properties. Single-crystal X-ray diffraction and energy dispersive X-ray spectroscopy analyses indicated the chemical composition to be Cs<inf>2</inf>Hf(Cl<inf>0.578(6)</inf>Br<inf>0.422(6)</inf>)<inf>6</inf> (= Cs<inf>2</inf>HfCl<inf>3.47(4)</inf>Br<inf>2.53(4)</inf>, approximately Cs<inf>2</inf>Hf(Cl<inf>0</inf> <inf>58</inf>Br<inf>0.42</inf>)<inf>6</inf>) where the number in the parentheses denotes the estimated standard deviation in the last digit. Cs<inf>2</inf>Hf(Cl<inf>0.58</inf>Br<inf>0.42</inf>)<inf>6</inf> was found to have a cubic Fm3‾m potassium hexachloroplatinate structure consisting of Cs⁺ cations and Hf(Cl<inf>0</inf> <inf>.</inf> <inf>58</inf>Br<inf>0.42</inf>)<inf>6</inf> ²⁻ anions. The emission peak of Cs<inf>2</inf>HfCl<inf>3</inf>Br<inf>3</inf> was red-shifted by Br substitution, and the photoluminescence decays of Cs<inf>2</inf>HfCl<inf>3</inf>Br<inf>3</inf> were accelerated when compared to those of Cs<inf>2</inf>HfCl<inf>6</inf>. Cs<inf>2</inf>HfCl<inf>3</inf>Br<inf>3</inf> had an emission peak at 450 nm under X-ray irradiation, while under UV-excitation, two photoluminescence emission peaks at 420 and 525 nm were observed. The decay profile of the 420-nm emission band had a single-exponential component with a decay time of 1.95 ± 0.01 μs under the 280-nm-excitation. On the other hand, 525-nm-emisison had two decay components of 0.28 ± 0.03 μs (11%) and 6.54 ± 0.03 μs (89%) under 305-nm-photons excitation.

DOI： 10.1016/j.optmat.2020.109942

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

A novel device structure "double layered thickness-shear resonator" was proposed to improve the temperature characteristics of a bulk acoustic wave resonator. In order to design the double layered resonator, optimal combination of cut angles and thickness ratio of the substrates were determined from calculations using material constants and their temperature coefficients measured for a Ca<inf>3</inf>TaGa<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (CTGS) single crystal. Based on the results, a double layered resonator was fabricated by directly bonding two CTGS substrates with cut angles of 122°Y and 171°Y under the thickness ratio of 0.248. As a result, the double layered resonator operated successfully at a fundamental mode of around 7.5 MHz like a normal resonator exhibiting temperature compensation effect. The mechanism of the deviation from the expected value observed in the measured temperature dependence of the frequency changes was discussed using the model of the wave propagation and the electric field generated in the double layer structure.

DOI： 10.35848/1347-4065/ab80da

Scopus

出版者・発行元：Crystals  

Ce-doped LaBr<inf>3</inf> /AEBr<inf>2</inf> (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman–Stockbarger (BS) method in quartz ampoules. The eutectics (AE = Mg and Ca) showed optical transparency like optical fiber bundles. A grown Ce-doped LaBr<inf>3</inf> /MgBr<inf>2</inf> eutectic shows a 355 nm emission ascribed to Ce³⁺ 4f-5d transition under X-ray excitation. The smaller the ionic size of AE, the higher the light yield of the sample was. The light yield of Ce:LaBr<inf>3</inf> /MgBr<inf>2</inf> was 34,300 photon/MeV, which is higher than Ce:LYSO standard. Scintillation decay time under 662 keV gamma-ray excitation was 18.8 ns.

DOI： 10.3390/cryst10070584

Open Access

Scopus

出版者・発行元：Crystals  

A novel single-crystal growth method was developed, using arc plasma and metal melt, for a quick survey of high melting point materials. Single crystals of Yb-doped Lu<inf>2</inf>O<inf>3</inf>, Lu<inf>0.388</inf>Hf<inf>0.612</inf>O<inf>1.806</inf>, and Lu<inf>0.18</inf>Hf<inf>0.82</inf>O<inf>1.91</inf>, with melting points of 2460, 2900, and 2840^◦C, respectively, were grown by an indirect heating method using arc plasma. We refer to this indirect heating growth method as the core heating (CH) method. The CH-grown Yb1%-doped Lu<inf>2</inf>O<inf>3</inf> sample showed a full width at half maximum of 286 arcsec in the X-ray rocking curve. This value is better than the 393 arcsec obtained for the crystal grown by the micro-pulling-down (µ-PD) method. The Yb charge transfer state (CTS) emission was observed at 350 nm in the Yb1%-doped Lu<inf>2</inf>O<inf>3</inf> and Lu<inf>0.18</inf>Hf<inf>0.82</inf>O<inf>1.91</inf>. In the case of the µ-PD method, using a rhenium (Re) crucible, absorption due to Re contamination and a resulting reduction in the Yb CTS emission were confirmed. However, contamination did not influence the properties observed in the crystals grown by the CH method.

DOI： 10.3390/cryst10070619

Open Access

Scopus

出版者・発行元：Journal of Crystal Growth  

Single crystal scintillators are extensively used in various radiation detection applications and their scintillation performances can be improved via co-doping. Therefore, in this study, tungsten-ion co-doped Ce:Gd<inf>3</inf>(Ga,Al)<inf>5</inf>O<inf>12</inf> (Ce:GGAG) crystals were grown using the micro-pulling-down (μ-PD) method to investigate the effects of co-doping on their scintillation properties. The relationships between the W concentration, optical and luminescence properties, and radiation response of the W-co-doped Ce:GGAG crystals were evaluated. The W-co-doped Ce 0.5%:Gd<inf>3</inf>Ga<inf>3</inf>Al<inf>2</inf>O<inf>12</inf> single crystals of diameter 3 mm and length 30–60 mm were grown by the μ-PD method. The light yield increased at W concentrations of 200 and 500 ppm and decreased at W concentrations above 1000 ppm. There was no significant change in the fast decay component of scintillation.

DOI： 10.1016/j.jcrysgro.2020.125513

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Effects of the tungsten (W) ions co-doping on the crystal growth, optical and scintillation properties for the Czochralski (Cz) grown Ce:Gd3Ga3Al2O12(GGAG) single crystals were investigated. The W 0%, 0.1%, 0.3%, 1%, and 5% co-doped Ce 1%:GGAG single crystals with a diameter of 1 in and length of 60-80 mm were grown by the Cz method. The effective segregation coefficient of the W ions was found as 0.002, 0.001, and 0.005 for W 0.1%, 0.3%, and 1%, Ce:GGAG, respectively. The segregation of W ions in GGAG host, light yield, and scintillation decay of the W co-doped Ce:GGAG were evaluated. The light yield decreased as the concentration of W co-dopant increased and toward the tail of the crystal. Furthermore, the defect role and related charge trapping in the W co-doped crystals were monitored by the thermo-stimulated luminescence.

DOI： 10.1109/TNS.2020.2968088

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

This article presents the development of diced SrI2:Eu arrays and their scintillation properties when coupled with a multipixel photon counter (MPPC) array. Using a dicing technique specific to halide scintillators, a high-energy resolution scintillator array is developed that is cost-effective and widely applicable. The developed SrI2:Eu arrays are of 3 × 3 × 3 mm3/pixel 4 × 4 matrix (TYPE1) and 1 × 1 × 1 mm3/pixel 9 × 9 matrix (TYPE2) structures. We fabricated test gamma-ray detector modules consisting of the TYPE1 and TYPE2 arrays coupled with an MPPC array. The mean peak to valleys ratio is 85.3 ± 14.9 for the TYPE1 array and 38.5 ± 16.6 for the TYPE2 array detector. The average energy resolutions obtained for the TYPE1 and TYPE2 gamma-ray detectors were 5.4 ± 0.4% full-width at half-maximum (FWHM) and 5.2 ± 0.6% FWHM, respectively, for 662-keV gamma-rays. The variation in the signal pulse height of the TYPE1 and TYPE2 detectors was only 10.6% and 10.4% in FWHM, respectively. These results demonstrated that the dicing technique proposed in this article could be applied to hygroscopic halide scintillators.

DOI： 10.1109/TNS.2020.2986460

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Carbazole crystals were grown using self-seeding vertical Bridgman technique, and the scintillation properties for neutron detection were investigated. Results of powder X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses indicated the single phase of the grown carbazole crystal with orthorhombic structure. Photo-and radio-luminescence measurements were carried out, and maxima of both emission peaks were at 420 nm. The light yield under 5.5-MeV alpha-ray irradiation was estimated to be 1.87 times higher than that of lithium glass GS-20. The scintillation decay time under neutron irradiation was estimated to be 11.4 ± 0.3 ns. It follows from the temperature dependence measurements that the light output under 662-keV gamma-ray excitation decreases with increasing temperature.

DOI： 10.1109/TNS.2020.2996276

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

A new red-emitting halide scintillator Rb2HfI6 was developed using the vertical Bridgman furnace and quartz ampoule. Under X-ray irradiation, Rb2HfI6 had a broad emission band of around 725 nm. The light output and energy resolution were determined to be 40000 photons/MeV and 7.4% (full-width at half-maximum at 662 keV), respectively. Since red photons are transmitted with smaller losses than blue or yellow photons inside an optical fiber, a long-fiber-reading radiation detection system using the high light-output red scintillator can be established for severe or hazardous environments. We fabricated the Rb2HfI6 scintillation crystal and performed the gamma-ray detection test under high-dose irradiation condition from a 60Co source with an activity of 100 TBq. The dynamic range of the Rb2HfI6 gamma-ray detection with a 20-m optical fiber was evaluated and compared with the previously developed Cs2HfI6 crystal and the conventional deep-red Cr: α-Al2O3 (ruby) scintillator. The gamma-ray doses from 0.4 to 1 kSv/h were successfully measured using Rb2HfI6 through the 20-m fiber.

DOI： 10.1109/TNS.2020.2976695

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

We measured the scintillation light yield of ZnWO4 crystals using a quasi-monochromatic neutron beam energy of 865 keV. Irradiating the neutron beam on two surfaces, which are almost perpendicular to the crystal axis, the light yield of oxygen recoil was measured. The obtained light yield ratio of a neutron recoil to gamma-ray-induced electron recoil for two surfaces was 0.235 ± 0.026 and 0.199 ± 0.020, respectively, which corresponds to 15.3% of anisotropy for 200-keV nuclear recoils of this crystal. This property can be applied to a direction-sensitive dark matter (DM) detector.

DOI： 10.1109/TNS.2020.2985027

Open Access

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Scintillation characteristics of Y<inf>0.8</inf>Gd<inf>2.2</inf> (Al<inf>5-x</inf>Ga<inf>x</inf>)O<inf>12</inf>:Ce,Mg ($x = 2.6$ and 3) single crystals are presented. At 662-keV $\gamma $-rays, the light yield of 35 600 photons/MeV obtained for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce,Mg is higher than that of 32 600 photons/MeV for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2.4</inf>Ga<inf>2</inf><inf>6</inf>O<inf>12</inf>:Ce,Mg. Scintillation decay components of 32.3 ns (52.4%) + 104 ns (47.6%) obtained for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce,Mg are faster than those of 11.5 ns (5%) + 51.2 ns (69%) + 302 ns (26%) obtained for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2.4</inf>Ga<inf>2</inf><inf>6</inf>O<inf>12</inf>:Ce,Mg. The coincidence time resolution of 336 and 389 ps was obtained, respectively, for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce,Mg-photomultiplier (PMT) and Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2.4</inf>Ga<inf>2</inf><inf>6</inf>O<inf>12</inf>:Ce,Mg-PMT, in coincidence experiment with a BaF<inf>2</inf>-PMT detector. The radioluminescence yield at room temperature (RT) is comparable for both crystals while the yield below 130 K is about 20% higher for Y<inf>0.8</inf>Gd<inf>2.2</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf>:Ce,Mg. Afterglow and thermally stimulated luminescence (TSL) below RT are also measured.

DOI： 10.1109/TNS.2020.2975734

Scopus

出版者・発行元：Journal of Crystal Growth  

The phase diagram of the BaI<inf>2</inf>-LuI<inf>3</inf> system was created using powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis, and a eutectic scintillator crystal was grown by the halide-vertical bridgman (H-VB) method. The results of XRD patterns and DSC curves showed that the phase diagram of the BaI<inf>2</inf>-LuI<inf>3</inf> system had a eutectic point around 77.5 mol% BaI<inf>2</inf>/22.5 mol% LuI<inf>3</inf>, and no new compound was generated from BaI<inf>2</inf> and LuI<inf>3</inf>. The 77.5 mol% BaI<inf>2</inf>/22.5 mol% LuI<inf>3</inf> eutectic crystal was composed of BaI<inf>2</inf> in rod phase and LuI<inf>3</inf> in matrix phase. In addition, the Ce-doped 77.5 mol% BaI<inf>2</inf>/22.5 mol% LuI<inf>3</inf> specimen showed emission peaks originating from 5d–4f transition of Ce³⁺ ion in the X-ray radioluminescence (XRL) spectrum and the decay time under γ-ray irradiation was approximately 38 ns.

DOI： 10.1016/j.jcrysgro.2020.125573

Scopus

出版者・発行元：Applied Physics Express  

We have developed a remote scintillation detector using a CCD spectrometer and a red-emitting scintillator coupled with a 20 m optical fiber for ultra-high-dose conditions. Gamma rays were detected with a conventional deep-red-emitting ruby scintillator and Cs<inf>2</inf>HfI<inf>6</inf>, which is a novel material with 700 nm red emission and a high light output. The scintillators were irradiated with gamma rays from a ⁶⁰Co source under an effective dose rate from ∼0.002 to ∼1 kSv h^-1. The integrated area of the Cs<inf>2</inf>HfI<inf>6</inf> emission spectra was larger than that of the ruby, and good linearity of the Cs<inf>2</inf>HfI<inf>6</inf> signal as a function of dose rate was confirmed.

DOI： 10.35848/1882-0786/ab77f7

Scopus

出版者・発行元：Journal of Crystal Growth  

Edge defined Film Fed Growth (EFG) method with molybdenum (Mo) crucible and die was studied for the growth of several oxide-based single crystals. At first, reactivity between the molybdenum (Mo) metal and oxide melts of Ce:(Lu,Y)<inf>2</inf>SiO<inf>5</inf> (LYSO) Ce:Y<inf>2</inf>SiO<inf>5</inf> (YSO), Ce:Gd<inf>3</inf>(Al,Ga)<inf>5</inf>O<inf>12</inf> (GAGG), Ce:Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (LuAG), Ce:Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (YAG) was investigated. The experimental and calculation results on the reactivity with Mo show that the aluminum garnets (LuAG, YAG) had the smallest reactivity with Mo metal. On the contrary, GAGG showed the strongest reaction with Mo. Then, the multiple-die grown shaped single crystal growth of Ce:LuAG was demonstrated by EFG method. Single crystal plates up to 320 mm in length were grown successfully. The homogeneity of dopant distribution, Mo contamination, luminescence and scintillation responses of the grown crystals were evaluated.

DOI： 10.1016/j.jcrysgro.2020.125510

Scopus

出版者・発行元：Journal of Luminescence  

Both the total luminescence yield (TLY) and the luminescence spectra of scintillators were measured to identify which scintillator exhibited high luminosity in the soft X-ray (SX) region from 300 eV to 1.3 keV. The TLY intensities and the peak intensities of the luminescence spectra were compared to identify the scintillators that have high luminosity for reducing the pixel size of a two-dimensional detector by applying the stimulated emission depletion phenomenon. The obtained TLY intensities were Tl:CsI, Eu:GGG, Ce:LYSO, Tb:LSO, Eu:YAP and Ce:YAP (in descending order of strength), which differs from the known luminosities in the hard X-ray region. The order of the measured TLY intensity and the change of order between the present and the previous values of luminosities can be explained by the number of secondary electrons generated in the base material of the scintillator in the SX region.

DOI： 10.1016/j.jlumin.2019.116850

Open Access

Scopus

出版者・発行元：Crystals  

The microstructure and mechanical properties of platinum (Pt) fibers fabricated by unidirectional solidification using the alloy-micro-pulling-down (A-μ-PD) method were investigated using a Universal Testing Machine and Electron Backscattered Diffraction (EBSD). The Pt fiber fabricated at a growth rate of 10 mm/min was composed of relatively large grains with <100> crystal orientation along the growth direction. The crystal orientation was consistent with the easy axis of the crystal growth on the face-centered-cubic (f.c.c.) structure. On the other hand, the adjacent grains of the Pt fiber fabricated at 50 mm/min were randomly oriented owing to a faster growth rate. In tensile tests, the Pt fibers fabricated by the A-μ-PD method indicated extremely different stress–strain curves compared to the commercial Pt wire. The maximum tensile stress of the Pt fiber reached ~100 MPa, and the Pt fiber ruptured after 58% nominal strain.

DOI： 10.3390/cryst10030216

Open Access

Scopus

出版者・発行元：Crystals  

Co-Cr-Mo alloy fibers of 2 mm in diameter were fabricated from the melt at 1, 2, and 5 mm/min growth rates by unidirectional solidification using an alloy-micro-pulling-down (A-µ-PD) method to control the microstructure. All elements, Co, Cr, and Mo, were distributed in stripes elongated along the growth direction due to constitutional undercooling. Both Co-Cr-Mo fibers fabricated at 2 and 5 mm/min growth rates were composed of the γ phase with a face-centered cubic structure (fcc-γ phase) and ε-phase with a hexagonal close-packed structure (hcp-ε phase), and the ratio of the fcc-γ phase in the fiber fabricated at 5 mm/min growth rate was higher than that in the fiber fabricated at 2 mm/min. The results suggest that a faster growth rate increases the ratio of the fcc-γ phase in the Co-Cr-Mo fiber fabricated by unidirectional solidification.

DOI： 10.3390/cryst10010011

Open Access

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

Tl:CsI/CsCl/NaCl eutectic scintillators were grown by the Bridgman-Stockbarger method. The eutectic phases were uniformly distributed in the transverse direction and slightly aligned along the growth direction. Then, the CsI phase can be designed as columnar. The expected emission peak observed at 550 nm was observed under X-ray excitation and cathodoluminescence and was ascribed to the self-trapped exciton perturbed by TI+ in Tl:CsI. The mapping of optically waveguided light emission was observed by confocal laser microscopy, consequently optical waveguiding of Tl+ emission in the CsI phase was demonstrated.

DOI： 10.35848/1347-4065/abcdab

Scopus

出版者・発行元：Acta Physica Polonica A  

Plate shaped Fe–Al alloy crystals were successfully grown using the µ-PD method. The orientation and grain size could be controlled by using the well oriented Fe0.95Al0.05 seed crystal. The as-grown Fe0.82Al0.18 and Fe0.80Al0.20 showed the magnetostriction 3/2λ = 121 and 149 ppm, respectively, which is comparable to the values for single crystal samples grown by the Bridgman-Stockbarger method. Distributions of Fe and Al were homogenous along the growth direction within standard deviations of 0.35% and 1.3%, respectively. A prototype vibration energy harvester was demonstrated using the grown Fe–Al alloys.

DOI： 10.12693/APhysPolA.137.1009

Open Access

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

A new experimental method to search for T-violating transverse muon polarization (P<inf>T</inf>) in the K⁺→π⁰μ⁺ν (K<inf>μ3</inf>) decay is proposed. In this new experiment, the measurements of the μ⁺ momentum vector, the π⁰ momentum vector, and the μ⁺ polarization will be performed by the same electro-magnetic calorimeter. One of key issues is the choice of a scintillation material which can preserve the μ⁺ spin polarization for several μ⁺ lifetimes. A test experiment to measure the residual μ⁺ polarization in a CeF<inf>3</inf> scintillating crystal was performed at J-PARC Material and Life Science Facility (MLF). We concluded that the residual μ⁺ polarization in CeF<inf>3</inf> is high enough to perform the new T-violation experiment.

DOI： 10.1016/j.nima.2019.162587

Scopus

出版者・発行元：2019 IEEE Nuclear Science Symposium and Medical Imaging Conference NSS Mic 2019  

Laser-driven neutron source is possible to obtain data with higher energy resolution than accelerator based neutron source. The purpose of this study is to evaluate the neutron pulse width for the energy spectrum emitted by the reaction between charged particles experimentally obtained by LFEX laser and a beryllium neutron production target. Monte Carlo simulation code of PHITS 3.02 was used for neutron pulse width evaluation.Furthermore, we investigate the candidate of scintillator for the detection of neutrons in laser-driven neutron source. It was confirmed that the neutron pulse width of a laser-driven neutron source was shorter than that of the accelerator based neutron source in the keV to MeV region. We also experimentally confirmed that organic scintillator such as p-terphenyl was the candidate for the detection of keV to MeV energy region neutron because of high light output and fast decay.

DOI： 10.1109/NSS/MIC42101.2019.9059945

Scopus

出版者・発行元：Journal of Solid State Chemistry  

Al concentration dependence of the crystal structure on Ca<inf>3</inf>Ta(Ga<inf>1-x</inf>Al<inf>x</inf>)Si<inf>2</inf>O<inf>14</inf> (CTGAS) piezoelectric single crystals were investigated by X-ray crystal structure analysis. O(2)-Si-O(2) and Si-O(2)-(Ga,Al) bond angles systematically increased with increasing Al concentration, and the result suggests that the increase of structural anisotropy by the Al substitution is attributable to the planarization of the O(2)-Si-O(2)-(Ga,Al). In addition, (Ga,Al)-O(2), (Ga,Al)-O(3) and Ca-O(1) bond lengths systematically decreased with increasing the Al substitution. The cation shift of the Si and (Ga,Al) ions out of center from the barycenter of the oxygen coordination environment decreased with increasing Al concentration.

DOI： 10.1016/j.jssc.2019.06.009

Scopus

出版者・発行元：Optical Materials  

Scintillation and luminescence properties of a novel organic crystal scintillator, 1,4-bis(2-methylstyryl)benzene (bis-MSB), were measured and compared with those of the conventional trans-stilbene organic crystal scintillator. Although trans-stilbene has been used for beta or neutron detection, trans-stilbene cannot be applied at high temperature conditions due to a lower melting point (124 °C). Liquid scintillators or plastic scintillators also cannot be used at high temperature. Usually, bis-MSB has been used as dopant in liquid scintillators to obtain fast scintillation decay and high luminescence quantum yield, and its melting point is 181 °C higher than that of trans-stilbene. In this paper, we focused on bis-MSB in solid state. The bis-MSB and trans-stilbene crystals were grown by the self-seeding vertical Bridgman method using double quartz ampoules. The bis-MSB crystal had the fast decay time of ∼4.2 ns and the increased light yield of ∼12,000 ph/5.5 MeV(α), while trans-stilbene had the decay time of ∼8.5 ns and the light yield of ∼8500 ph/5.5 MeV(α). The photoluminescence quantum yield was almost constant up to 125 °C for bis-MSB and only up to 50 °C for trans-stilbene. We succeeded in obtaining the novel organic crystal scintillator which can operate even at higher temperature up to 125 °C.

DOI： 10.1016/j.optmat.2019.04.051

Scopus

出版者・発行元：Radiation Measurements  

Pyrosilicate scintillation crystals are expected to be the next generation scintillators, because they have good light output and no hygroscopic nature. In this work, (Ce<inf>0.01</inf> Gd<inf>0.90</inf> Y<inf>0.09</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (Ce:Y-GPS)crystal was grown by the floating zone method. Emission wavelengths of this material were at 360 and 380 nm originated from Ce³⁺ 5d-4f transition, and these emission peaks were located at shorter wavelength side compared with Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> due to the change of the crystal field. Gamma-ray-excited pulse height and scintillation decay measurements showed that Ce:Y-GPS had a light output of 48,000 ± 3000 photons/MeV, FWHM energy resolution of 11.8 ± 0.5% at 662 keV and the decay time components of 42 ± 1 ns (58 ± 2%)and 180 ± 10 ns (42 ± 2%).

DOI： 10.1016/j.radmeas.2019.106123

Scopus

出版者・発行元：Radiation Measurements  

Cesium hafnium iodide (CHI) was reported as a novel red-emitting scintillator in our previous article, while optimization of the crystal quality and evaluation of the scintillation performance were insufficient. In this study, a large and transparent CHI single crystalline specimen was obtained using slow crystal growth speed. Coupled with a Si avalanche photo-diode, the full width at half maximum energy resolution was evaluated to be 4.2 ± 0.2% at 662 keV which was the best value among conventional red-emitting scintillators. The scintillation light output, non-proportional response of light output and scintillation decay were also evaluated with a photomultiplier tube.

DOI： 10.1016/j.radmeas.2019.03.005

Scopus

出版者・発行元：Journal of Electronic Materials  

Undoped and Nb-doped SrTiO <inf>3</inf> /TiO <inf>2</inf> (STO/TO) eutectic solids were fabricated from the melt at a eutectic point of STO and TO by unidirectional solidification. Fabricated undoped and Nb:STO/TO eutectic solids were composed of the TiO <inf>2</inf> rod-like and the SrTiO <inf>3</inf> matrix phases, and the periodic and uniform eutectic morphology could be achieved in the Nb:STO/TO eutectic solids by stable control of the liquid–solid interface during the fabrication. The thermal conductivity of the Nb:STO/TO eutectic solid was less than half of that of the Nb:STO single crystal owing to the decrease of the lattice thermal conductivity by phonon scattering at the grain boundaries. The figures of merit ZT’s of the Nb:STO/TO eutectic solid, parallel and perpendicular to the growth direction, were ∼ 0.007 and ∼ 0.0004, respectively. The small ZT’s are attributable to the higher electrical resistivity originating from the insufficient carrier doping and high electrical resistivity of the TO phase.

DOI： 10.1007/s11664-018-06880-2

Scopus

出版者・発行元：Optical Materials  

Ce:(Gd,La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (Ce:La-GPS) and Al co-doped Ce:(Gd,La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (Al,Ce:La-GPS) single crystals were grown by the micro-pulling-down method to improve the mechanical, optical and scintillation properties. In a tensile test, the maximum strain and stress values in the stress-strain curve of the Al,Ce:La-GPS single crystal compared to the Ce:La-GPS single crystal and the result suggests that there is a possibility of the improvement on the mechanical property by Al co-doping. In addition, the light yield of the La-GPS single crystal under γ-ray irradiation was slightly increased and the decay time was accelerated by the Al co-doping.

DOI： 10.1016/j.optmat.2018.07.067

Scopus

出版者・発行元：Optical Materials  

GdTaO<inf>4</inf> and (Gd<inf>1-x</inf>Tb<inf>x</inf>)TaO<inf>4</inf> (x = 0, 0.001, 0.02, 0.04, 0.10, and 0.16) single crystals were grown by the micro-pulling down method. The crystallographic system of the grown crystals was identified to be monoclinic (I2/a), which is the stable low-temperature phase of GdTaO<inf>4</inf>. In the photoluminescence (PL) spectra, intense emission was observed at 549 nm (⁵D<inf>3</inf>→⁷F<inf>4</inf> transition of Tb³⁺) for every Tb doped GdTaO<inf>4</inf>. In the excitation spectra for the 549 nm emission, several excitation paths to the Tb³⁺ were attributed: 4f-4f transitions of Gd³⁺, 4f⁸-4f⁷5d transitions of Tb³⁺ and charge transfer of TaO<inf>4</inf> ³⁻ group. Radiolumincece spectra under X-ray irradiation were taken, and the highest emission peak was observed at 544 nm, which was ascribed to the ⁵D<inf>4</inf>→⁷F<inf>5</inf> transition of Tb³⁺. The Tb 2% doped GdTaO<inf>4</inf> showed the highest emission intensity at the 544 nm, and as increasing dopant concentration, the intensity decreased due to the cross-relaxation of Tb³⁺.

DOI： 10.1016/j.optmat.2018.05.031

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

Ca<inf>3</inf>TaAl<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (CTAS) piezoelectric powders were sintered at various temperatures to investigate phase formation. The CTAS powder sintered at 1350 °C was composed of a main phase with a langasite-type structure in addition to two secondary phases, whereas the main phases of the CTAS powders sintered at 1200 and 1300 °C were the secondary phases in X-ray diffraction patterns. CTAS single crystals with a diameter of 1 in. were grown by a Czochralski method using the sintered powders, and CTAS single crystals without impurity phases could be grown using the powder sintered at 1350 °C. A higher sintering temperature of starting materials contributes to the creation of CTAS single crystals without impurity phases.

DOI： 10.7567/JJAP.57.11UD11

Scopus

出版者・発行元：Journal of Crystal Growth  

Fabrication of scintillating eutectic composites by various directional solidification techniques is introduced and discussed in some details. Number of methods widely practiced for the single crystal growth including Czochralski, Bridgman or vertical zone melting, and micro-pulling-down are also acceptable for the production of eutectic materials. Two types of such materials are considered here. These are (1) composites used for neutron scintillators; eutectic materials that consist of high neutron cross section material and efficient scintillator (they do not require regular micro-structure) and (2) high resolution scintillators; eutectic materials that have well ordered rod/fiber structure of one of the phases immersed into matrix of second phase (one of them should be efficient scintillator). In later one, the wave guiding can be established in one of the phases (either matrix or fibers). The composites with fiber structure are supposed to be very promising substances for detecting initial irradiation with high spatial resolution. LiF/LiYF<inf>4</inf> and LiF/CaF<inf>2</inf>:Eu eutectic composites represent first group of the scintillators, but CsI/NaCl and GdAlO<inf>3</inf>/α-Al<inf>2</inf>O<inf>3</inf> correspond to the second one.

DOI： 10.1016/j.jcrysgro.2018.02.032

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Ce-doped (Gd, La) <inf>2</inf> Si <inf>2</inf> O <inf>7</inf> (Ce:La-GPS) scintillator was found to have a good light output of around 40 000 photons/MeV, while some other parameters have not been determined so far. In order to clarify the cause for such a high light yield, some physical parameters have been estimated in this paper. The bandgap energy of Ce:La-GPS was evaluated to be over 7.13 ± 0.03 eV for (Gd <inf>0.75</inf> , La <inf>0.25</inf> ) <inf>2</inf> Si <inf>2</inf> O <inf>7</inf> . Although Ce:La-GPS had wider bandgap compared with the other oxide scintillators, its light output was larger than values for some other scintillators. Since quantum yield of Ce:La-GPS was as high as around 0.8, the product of transfer efficiency and electron-hole pair generation efficiency was estimated to be around 0.9, which was higher than for the other scintillators. Thus, Ce:La-GPS was suggested to have high the product of transfer efficiency and/or electron-hole pair generation efficiency.

DOI： 10.1109/TNS.2018.2841917

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Nondoped Cs<inf>2</inf>HfCl<inf>6</inf> (CHC) and alkaline earth metal-doped CHC (AE:CHC) crystals were grown by the vertical Bridgman-Stockbarger method. The spectra of the AE:CHC under X-ray excitation were similar to those for the AE-free crystal; thus, AE doping did not change emission wavelength of CHC. We determined the light outputs and energy resolutions of nondoped CHC and AE:CHC by measuring pulse-height spectra under 662-keV gamma-ray excitation of a ¹³⁷Cs source. Both light output and energy resolution were deteriorated with AE doping. For example, nondoped CHC had a light output of 44 000 photons/MeV and energy resolution of 5.2%; on the other hand, Sr 0.5 at.%-doped CHC had a light output of only 28 000 photons/MeV and energy resolution of 10%. Scintillation decay also did not change. The nonproportional response values of light output versus gamma-ray energy did not improve in AE:CHC either. Therefore, doped AEs can be responsible for creation of defect trap levels which would hamper the carrier transport in CHC structure.

DOI： 10.1109/TNS.2018.2848474

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Submicrometer diameter phase-separated scintillator fibers (PSSFs) were reported and they possessed both the properties of an optical fiber and radiation-to-light conversion. The PSSFs were fabricated using a directionally solidified eutectic system. High-resolution X-ray imaging can be developed using the PSSFs. In this paper, Tb- and Eu-doped GdAlO<inf>3</inf> (GAP)/ α-Al<inf>2</inf>O<inf>3</inf> eutectic scintillator was grown by the micro pulling down method with various growth rates in order to achieve the high light output and the high light-guiding efficiency. Relationship between radioluminescence intensity and dopant concentration of Eu and Tb was investigated. At the optimized dopant concentration, relationship between growth rate, eutectic period structure, diameter of PSSFs, and contrast transfer function was investigated to achieve high-resolution X-ray imaging.

DOI： 10.1109/TNS.2018.2841026

Scopus

出版者・発行元：Crystal Growth and Design  

The sealed vertical Bridgman (VB) method is the main technique used to grow SrI<inf>2</inf>(Eu) crystals because SrI<inf>2</inf>(Eu) is very hygroscopic. In this study, we grew SrI<inf>2</inf>(Eu) single crystals with two-inch diameters and four-inch lengths using the VB method equipped with a removable chamber. The SrI<inf>2</inf>(Eu) single crystals were produced by the Liquinert process, which requires careful consideration of the crucible material and growth atmosphere. After a review of available materials, carbon crucibles were selected due to their several advantages over traditional quartz ampules: (1) they are suitable for large size crystal growth due to which they do not require any process for sealing of quartz ampule before the growth; (2) ease in controlling the temperature gradient because carbon crucibles can be heated directly via a high frequency induction heating system; and (3) carbon crucibles can assist in removing oxygen and moisture from the melt. The starting material, seed, and hot zone were prepared inside the glovebox in the removable growth chamber, which was used as the growth unit. This unit was installed in the growth system and heated to the melting point of SrI<inf>2</inf>(Eu) in a high-purity Ar atmosphere. The crucible in the growth chamber was then displaced in the downward direction for crystal growth. Crack-free SrI<inf>2</inf>(Eu) bulk single crystals with two-inch diameters were produced. The crystals were cut into cylindrical specimens (diameter = length = 2 in.), polished, and sealed in an aluminum case with a quartz glass window for evaluation. Negligible self-absorption was observed because of the large length of the crystal. The light output of the SrI<inf>2</inf>(Eu) examined in this study was estimated to be 70 000 photons/MeV, and the calculated energy resolution was 3.4% (662 keV, full width at half-maximum) at room temperature.

DOI： 10.1021/acs.cgd.7b01044

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

CeBr<inf>3</inf> and Pr-doped CeBr<inf>3</inf> (Pr:CeBr<inf>3</inf>) single crystals were grown by the halide-micro-pulling-down method, and the effects of Pr doping on the optical and scintillation properties of the CeBr<inf>3</inf> single crystal were investigated. The emission peaks originating from the 4f-4f transition of Pr³⁺ions were observed in the photoluminescence spectrum of the Pr:CeBr<inf>3</inf> single crystal in addition to the emission peaks related to the 5d-4f transition of Ce³⁺ ions. The decay of fast and slow components under gamma-ray irradiation systematically accelerated with increasing Pr concentration while the light yield decreased.

DOI： 10.7567/JJAP.57.070312

Scopus

出版者・発行元：Journal of Crystal Growth  

In order to obtain new scintillators with high light output and high effective atomic number (Z<inf>eff</inf>), we performed anion-substitution for Cs<inf>2</inf>HfCl<inf>6</inf> (CHC) scintillator, and then, we succeeded in growing Cs<inf>2</inf>HfI<inf>6</inf> (CHI) single crystalline scintillator. It had Z<inf>eff</inf> of 58, which is the same as that of CHC, and had high light output of ∼70,000 photons/MeV with 700 nm emission. However, its scintillation decay time of ∼2.5 µs was slow for practical use as gamma-ray monitor. In this study, we performed Ce³⁺/Eu²⁺ doping to Hf⁴⁺ site to improve decay time of CHI, introducing the fast 5d-4f luminescence. Ce:CHI and Eu:CHI single crystals were finally obtained by the vertical Bridgman-Stockbarger method. The luminescence spectra of the Ce:CHI and Eu:CHI were very similar to that of the non-doped CHI, which would mean that no 5d-4f luminescence of Ce³⁺/Eu²⁺ was observed. The measured light output and decay time of Ce:CHI were ∼48,000 photon/MeV and 2.3 ± 0.1 µs, respectively. As for Eu:CHI, light output and decay time were ∼69,000 photon/MeV and 2.8 ± 0.1 µs, respectively.

DOI： 10.1016/j.jcrysgro.2018.03.033

Scopus

出版者・発行元：Journal of Crystal Growth  

ZnAl<inf>2</inf>O<inf>4</inf> crystals were grown using few starting compositions with various ZnO:AlO<inf>3/2</inf> ratio using an Ir wire seed and Ir + Re crucible under ordinary pressure with Ar + 2%O<inf>2</inf> atmosphere by the radiofrequency heating µ-PD furnace. The ZnAl<inf>2</inf>O<inf>4</inf> spinel single crystal with 4 mm diameter could be successfully grown by the µ-PD method by optimization of starting melt composition considering with Zinc oxide evaporation. During 10 min of growth under normal pressure the formation of ZnAl<inf>2</inf>O<inf>4</inf> single phase observed even at high vapor pressure of ZnO. The transmittance spectra and X-ray locking curve were measured for evaluating of grown ZnAl<inf>2</inf>O<inf>4</inf> crystals quality.

DOI： 10.1016/j.jcrysgro.2018.03.009

Scopus

出版者・発行元：Journal of Crystal Growth  

This paper addresses several aspects of the µ-PD growth technology as applied to submillimeter diameter sapphire tubes for UFD application. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. A compound crucible made possible the growth of single crystal sapphire tube as small as around 0.70–0.72 mm in outer diameter and 0.28–0.29 in inner diameter over 160 mm in length at growth rate of 2–4 mm/min along 〈0 0 1〉 direction. An Ir crucible with a die composed of an equivalent hole and Ir wire was heated by RF coil in N<inf>2</inf> atmosphere. The μ-PD method has been successfully adapted for single crystal sapphire tube growth. Grown crystal tube showed good XRC value of 30.2 arcsec.

DOI： 10.1016/j.jcrysgro.2018.03.023

Scopus

出版者・発行元：Journal of Alloys and Compounds  

Single crystals of (La<inf>0.25</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> and (La<inf>0.235</inf>Ce<inf>0.015</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> were grown by the Czochralski method. Structure analysis of the single crystals by X-ray diffraction (XRD) revealed that (La<inf>0.25</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> and (La<inf>0.235</inf>Ce<inf>0.015</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> crystalize in monoclinic cells (space group P2<inf>1</inf>/c), a = 5.3905(8) Å, b = 8.5605(11) Å, c = 13.957(2) Å, β = 112.223(6)º, and a = 5.3921(7) Å, b = 8.5688(10) Å, c = 13.9172(14) Å, β = 111.980(5)º, respectively. One of the two different rare-earth sites is preferentially occupied by La and Gd atoms or by La, Ce and Gd atoms, and the other is occupied by Gd atoms only. Peaks attributed to the 4f-4f transitions (⁸S<inf>7/2</inf>–⁶G<inf>7/2</inf> and ⁸S<inf>7/2</inf>–⁶I<inf>x</inf>) of Gd³⁺ and 4f-5d transitions of Ce³⁺ were observed in the absorption spectra of (La<inf>0.25</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> and (La<inf>0.235</inf>Ce<inf>0.015</inf>Gd<inf>0.75</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystals.

DOI： 10.1016/j.jallcom.2018.02.286

Scopus

出版者・発行元：Journal of Crystal Growth  

Eu-doped Li(Ca,Sr)AlF<inf>6</inf> [Eu:LiCSAF] single crystals with various Ca/Sr ratios were grown by the micro-pulling-down method, and their optical and scintillation properties were investigated to reveal the effects of Ca/Sr ratio on optical and scintillation properties of the Eu:LiCSAF single crystals. The Li(Ca<inf>1−</inf> <inf>x</inf> <inf>−</inf> <inf>y</inf>Sr<inf>x</inf>Eu<inf>y</inf>)AlF<inf>6</inf> single crystals could be grown in 0 ≤ x ≤ 0.1, 0.5 ≤ x ≤ 1.0 and y = 0.02 while the Eu:LiCSAF crystals with x = 0.2, 0.25 and 0.4 included two colquiriite-type phases with different lattice parameters. The Li(Ca<inf>1−</inf> <inf>x−y</inf>Sr<inf>x</inf>Eu<inf>y</inf>)AlF<inf>6</inf> single crystal with x = 0.25 and y = 0.02 showed the highest light yield under neutron irradiation.

DOI： 10.1016/j.jcrysgro.2018.03.022

Scopus

出版者・発行元：Journal of Crystal Growth  

Pr-doped SrI<inf>2</inf> (Pr:SrI<inf>2</inf>) single crystals with various Pr concentrations were grown by the halide-micro-pulling-down (H-μ-PD) method, and the scintillation properties were investigated. Pr1%:SrI<inf>2</inf> single crystal with high transparency could be grown by the H-μ-PD method while Pr2, 3 and 5%:SrI<inf>2</inf> single crystals included some cracks and opaque parts. In the photoluminescence spectrum of the Pr1%:SrI<inf>2</inf> single crystal, an emission peak originated from the Pr³⁺ ion was observed around 435 nm while the radioluminescence spectra showed an emission peak around 535 nm for the undoped SrI<inf>2</inf> and Pr:SrI<inf>2</inf> single crystals. Light yields of Pr1, 2, 3 and 5%:SrI<inf>2</inf> single crystals under γ-ray irradiation were 7700, 8700, 7200 and 6700 photons/MeV, respectively. Decay times of Pr1 and 2%:SrI<inf>2</inf> single crystals under γ-ray irradiation were 55.9 and 35.0 ns of the fast decay component, and 435 and 408 ns of the slow decay component, respectively.

DOI： 10.1016/j.jcrysgro.2018.02.025

Scopus

出版者・発行元：Journal of Crystal Growth  

The fabrication and thermal electromotive force characteristics of Ir/Ir-Rh thermocouples capable of repeated bending deformation are described. Ir and Ir-Rh wires with a diameter of 0.5 mm were fabricated using the alloy-micro-pulling-down method. Scanning electron microscopy and electron backscattering diffraction of the radial cross section of the grown wires were performed to investigate the microstructure and orientation of the crystal grains. At the start of growth, the microstructure was polycrystalline with diameters of several hundred micrometers, while at the 8-m growth point it was found to be monocrystalline. The observed single crystals of pure Ir and Ir-Rh alloy were oriented in the 〈1 1 3〉 and 〈1 1 2〉 directions, respectively, whereas the polycrystalline Ir-Rh samples showed preferential growth in the 〈1 0 0〉 direction. The thermal electromotive force of the fabricated Ir/Ir-Rh thermocouple was measured by the comparison technique and the fixed-point technique, and the thermoelectric power was estimated to be 5.9 μV/°C in the range from 600°C to 1100°C.

DOI： 10.1016/j.jcrysgro.2018.01.018

Scopus

出版者・発行元：Journal of Crystal Growth  

Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillation crystals are expected to be used as gamma-ray detectors for high temperature measurement. To realize scintillators for high temperature environment, we investigated (Ce<inf>0.01</inf> Gd<inf>0.59−x</inf> La<inf>0.40</inf> Y<inf>x</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (x = 0.00, 0.05, 0.10, 0.15) single crystals grown by the micro-pulling-down method. The results showed that a 5% Y-admixed Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator can yield higher light output when compared with Y-free Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator. The light outputs at 25°C and 175°C were determined to be ∼43,000 and ∼40,000 photons/MeV, respectively. Moreover, 1 inch size 5% Y-admixed Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator was grown by the Czochralski technique, and its light output at 175°C kept the value of around 95% of the value at 25°C.

DOI： 10.1016/j.jcrysgro.2018.01.016

Scopus

出版者・発行元：Journal of Crystal Growth  

Ca<inf>3</inf>Ta(Ga<inf>0.9</inf>Sc<inf>0.1</inf>)<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> langasite-type single crystal with a diameter of 1 in. was grown by Czochralski (Cz) method. Obtained crystal had good crystallinity and its lattice constants exceeded those of Ca<inf>3</inf>TaGa<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (CTGS) according to the X-ray analysis. A crack-free specimen cut from the grown crystal was used for the measurements of dielectric constant ε<inf>11</inf>^T/ε<inf>0</inf>, electromechanical coupling factor k<inf>12</inf>, and piezoelectric constant d<inf>11</inf>. The accuracies of these measurements were better than those for the crystal grown by micro-pulling-down (μ-PD) method. Substitution of Ga with Sc resulted modification of these constants in the directions opposite to those observed after partial substitution of Ga (of CTGS) with Al. This suggests that increase of |d<inf>14</inf>| was most probably associated with enlargement of average size of the Ga sites. The crystal reported here had greater dimensions as compared to analogous crystals grown by the μ-PD method. As a result, accuracy of determination of acoustic constants of this material may be improved.

DOI： 10.1016/j.jcrysgro.2017.12.041

Scopus

出版者・発行元：Plasma and Fusion Research  

This paper presents the study of prospective organic-based materials, trans-stilbene and p-terphenyl, as their potential application for new neutron scintillators. Growth of their single crystals by the self-seeding vertical Bridgman method is reported. And evaluation of grown crystals concerning the composition, optical and luminescence properties, and scintillation performance at room temperature is discussed. Their photo-and radioluminesce spectra were peaking at 388 and 408 nm, their quantum yield was of 52.4% and 79.7%, and the light yield were of 0.89 and 1.80 times higher than that of GS-20 standard, respectively. The scintillation decay times of 8.2 ns (trans-stilbene) and 5.8 ns (p-terphenyl) were observed as well.

DOI： 10.1585/pfr.13.2405011

Open Access

Scopus

出版者・発行元：Aip Advances  

Colquiriite-type Eu-doped LiCaAlF<inf>6</inf> and LiSrAlF<inf>6</inf> (Eu:LiCAF and Eu:LiSAF) scintillator single crystals were grown using Al metal as a starting material to improve the Eu dopant segregation. All Eu:LiCAF and Eu:LiSAF single crystals using Al metal (Eu,Al^M:LiCAF and Eu,Al^M:LiSAF) indicated high transparency and effective segregation coefficients (k<inf>eff</inf>) of Eu2%,Al^M1%:LiCAF and Eu2%,Al^M1%:LiSAF single crystals were significantly improved to the value of 0.40 and 0.99, respectively. EuF<inf>3</inf> starting material reacted with Al metal before colquiriite-type phase was generated. As a result, Eu³⁺ ion in EuF<inf>3</inf> was changed to Eu²⁺ ion which could be incorporated into Ca²⁺ and Sr²⁺ sites easily.

DOI： 10.1063/1.5006996

Open Access

Scopus

出版者・発行元：Optical Materials  

Melt growth of scintillating halide crystals is reviewed. The vertical Bridgman growth technique is still considered as very popular method that enables production of relatively large and commercially attractive crystals. On the other hand, the micro-pulling-down method is preferable when fabrication of small samples, sufficient for preliminary characterization of their optical and/or scintillation performance, is required. Moreover, bulk crystal growth is also available using the micro-pulling-down furnace. The examples of growths of various halide crystals by industrially friendly melt growth techniques including Czochralski and edge-defined film-fed growth methods are also discussed. Finally, traveling molten zone growth that in some degree corresponds to horizontal zone melting is briefly overviewed.

DOI： 10.1016/j.optmat.2017.03.043

Scopus

出版者・発行元：Radiation Measurements  

The development of a real-time dose monitor system is one of the important issues in medical engineering to reduce medical accidents such as overdose or incorrect positioning of the treated human tissue during radiation therapy. One of the challenging solutions is to use an infrared scintillator, which is sufficiently bright so that the light can be detected outside the human tissue. In this study, a novel infrared scintillator, Cr-doped Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf>, was tested with pork meat as a phantom of human tissue to prove its feasibility for the dose monitor. The scintillation photons of Cr:Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> were observed through even 50-mm thick pork meat. The emission peak originated from d-d emission of Cr³⁺. The emission intensity of Cr:Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> was approximately 3.5 times larger than that of the conventional infrared scintillator Cr:α-Al<inf>2</inf>O<inf>3</inf>. Moreover, we succeeded in performing the infrared imaging for Cr:Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> irradiated with alpha-rays using a complementary metal oxide semiconductor camera.

DOI： 10.1016/j.radmeas.2017.03.028

Scopus

出版者・発行元：Journal of Materials Science Materials in Electronics  

In this study, Eu and Ce doped LiSrI<inf>3</inf> single crystals were explored and the scintillation performance was reported at the first time. Eu and Ce doped LiSrI<inf>3</inf> single crystals were grown by the Bridgman–Stockbarger method in a quartz ampoule with 3 mm inner diameter. Growth rate was 0.06 mm/min. Circular samples with 1 mm thickness were obtained from the grown crystal. The grown Eu doped LiSrI<inf>3</inf> crystal demonstrated Eu²⁺ 4f–5d emission peak at 420 nm under alpha-ray excitation. In the case of Ce doped one, double emission peaks at 360 and 400 nm were observed. The light yield of the Eu doped LiSrI<inf>3</inf> was around 35,000 photon/MeV for 662 keV gamma-ray and 24,000 photon/5.5 MeV for alpha-ray. Energy resolution of the Eu doped LiSrI<inf>3</inf> was 5.2%@662 keV. Scintillation decay time of the grown Ce and Eu doped LiSrI<inf>3</inf> under 662 keV gamma-ray was 23.8 ns (50%) 212 ns (50%) and 545 ns 100%, respectively.

DOI： 10.1007/s10854-017-7150-9

Scopus

出版者・発行元：Ceramics International  

Ca<inf>3</inf>Ta(Ga<inf>1-x</inf>Sc<inf>x</inf>)<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> (CTGSS) single crystals with various Sc concentrations (x = 0, 0.1, 0.2, 0.3, and 0.4) were grown by the micro-pulling-down method and their structure and chemical composition were evaluated. Through the powder X-ray diffraction (XRD) measurement and backscattered electron (BSE) imaging, it was demonstrated that all the CTGSS crystals with different Sc concentration were successfully grown as langasite-type structure although some secondary phases were observed for the crystals with x = 0.2, 0.3 and 0.4. Lattice parameters calculated from the powder XRD pattern generally increased with Sc substitution. Measured parameters for CTGSS crystal with x = 0.1 were larger permittivity ε<inf>11</inf>^T/ε<inf>0</inf> and lower electromechanical coupling coefficient k<inf>12</inf> and piezoelectric constant d<inf>11</inf> than those for CTGS crystal with x = 0. It was also suggested that piezoelectric constant |d<inf>14</inf>| became larger due to the Sc substitution.

DOI： 10.1016/j.ceramint.2017.05.272

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

The temperature dependences of the acoustic properties of Ca<inf>3</inf>Ta(Ga<inf>1-x</inf>Al<inf>x</inf>)<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> [CTGAS(x)] were experimentally studied as a function of the Al substitution content x. Five specimens, i.e., one each of X-, Y-, and Z-, and two rotated Y-cut specimens, were prepared from each crystal ingot of CTGAS(x) (x = 0, 0.25, 0.50, and 0.75) grown by the Czochralski technique. The longitudinal wave and shear wave velocities of CTGAS (x) were measured at three temperatures ranging from 291 to 300 K, then acoustically related physical constants (elastic, piezoelectric, and dielectric constants and coefficient of thermal expansion) were determined at approximately room temperature. The results revealed that the temperature coefficients of all the constants linearly changed with Al content. By one of the calculations using the constants and their temperature coefficients determined in this study, we demonstrated their capability to predict suitable conditions (i.e., cut angle, propagation direction, and chemical composition) for acoustic wave devices although they were determined in a narrow temperature range.

DOI： 10.7567/JJAP.56.07JB03

Scopus

出版者・発行元：Journal of Crystal Growth  

Ce-doped Lu<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator contains radioactive isotope ¹⁷⁶Lu which causes an unwanted intrinsic background signal. The development of scintillators with reduced Lu concentration were required in some applications. In this study, we developed the Gd admixed lutetium pyrosilicate, where the average ion radius at the rare earth site was similar to the Tm³⁺ ion radius, for which the RE<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (RE=Tm, Yb, Lu) crystal structure is stable from room temperature to melting point. We have grown (Ce<inf>x</inf> Lu<inf>1−x−y</inf> Gd<inf>y</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (x=0.01, y=0.00, 0.05, 0.10) single crystals. Their crystal systems were monoclinic with a space group C2/m. The absorption spectra revealed the energy transitions in Ce and Gd ions might be occurred. The light output was degraded and decay time was accelerated comparing the Gd 5% admixed sample with the Gd 10% one.

DOI： 10.1016/j.jcrysgro.2016.10.074

Scopus

出版者・発行元：Journal of Crystal Growth  

Mg co-doped Ce1%:Gd<inf>3</inf>Ga<inf>x</inf>Al<inf>5−x</inf>O<inf>12</inf> (Ce:GAGG) crystals (x=2.4, 2.7, 3.0) were successfully grown by the Czochralski (Cz) method. Effect of Mg co-doping on the scintillation properties of Ce:GAGG was examined. This study covers measurements of solidification fraction and scintillation properties such as light yield, energy resolution and non-proportionality for each crystal. Pulse-height spectra of various gamma and X-ray sources with energies ranged from 30 keV to 662 keV were measured. Regardless of the presence/absence of Mg dopant, the non-proportionality curves with lower content of gallium in the crystal structure tend to improve. Mg co-doped Ce:GAGG samples did not show a significant difference as compared with non co-doped Ce:GAGG. Mg co-doped crystals with x=2.4 and 2.7 showed the promising scintillation properties of faster decay time and higher energy resolution than those with x=3.0.

DOI： 10.1016/j.jcrysgro.2016.12.054

Scopus

出版者・発行元：Journal of Crystal Growth  

Na co-doped Eu: LiCaAlF<inf>6</inf> (Eu, Na: LiCAF) single crystals were grown by the micro-pulling-down (μ-PD) method, and their optical and scintillation properties were examined to reveal the effects of the Na co-doping. The crystals were single-phase materials demonstrating structure isomorphic with that of undoped LiCAF. To perform the crystals characterization, the specimens with dimensions of several millimeters were cut from highly transparent and crack free fragments of the crystals and polished. It was observed that Na co-doping resulted modification of the transmittance and the excitation spectra, and increased the light yield detected under neutron irradiation.

DOI： 10.1016/j.jcrysgro.2016.11.012

Scopus

出版者・発行元：Journal of Crystal Growth  

The relationship among lattice constant a, Al content, and acoustic properties were experimentally examined using a plate specimen perpendicular to Y-axis prepared from Ca<inf>3</inf>Ta(Ga<inf>0.75</inf>Al<inf>0.25</inf>)<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> [CTGAS(0.25)] single crystal grown by Czochralski method. As the acoustic properties, leaky surface acoustic wave (LSAW) velocities with different propagation directions, X- and Z-propagations, and longitudinal wave velocity propagating along Y-axis direction were measured by the line-focus-beam/plane-wave ultrasonic-material-characterization (LFB/PW-UMC) system. The measured results of LSAW velocity distributions revealed inhomogeneity in radial direction of the crystal ingot exhibiting lower velocity area at the center of the ingot. In addition, the distributions of lattice constant a and chemical composition (especially Al content) were measured along the radial direction. Abnormal changes suggesting existence of residual stresses concentrated on the central part of the crystal ingot other than the effect of chemical composition change were detected from the relationships among the measured parameters.

DOI： 10.1016/j.jcrysgro.2016.10.040

Scopus

出版者・発行元：Optical Materials  

Eu doped LiSrI<inf>3</inf>/LiI eutectics were grown by the Bridgman method in a quartz ample with 4 mm inner diameter. and their directionally solidified eutectic system has been investigated. Growth rate was 0.3 mm/min. The eutectic showed well aligned eutectic structure and optically transparent. Grown Eu doped LiSrI3/LiI eutectic shows 400 nm emission ascribed to Eu²⁺ 4f-5d transition under X-ray excitation. The light yield was around 26,000 photon/MeV for 662 keV gamma-ray and 35,000 photons for 5.5 MeV alpha-ray.

DOI： 10.1016/j.optmat.2017.05.010

Scopus

出版者・発行元：Optical Materials  

Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillators have fast decay time and keep high light output even at high temperature (∼150°C). To improve the scintillation properties such as light output and decay time, Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillators codoped with the divalent ions (e.g. Mg²⁺, Ca²⁺) have been studied. In this study, we focused on the other divalent ions (Sr²⁺ and Ba²⁺), and investigated their effect on the scintillation properties and temperature dependence of light output. The absorption due to Ce⁴⁺ was not observed for Sr or Ba codoping. The light outputs were degraded by Sr²⁺ or Ba²⁺ codoping, while the decay times at room temperature were not changed for the samples codoped with divalent ions. On the other hand, the temperature dependence of light output for Ba-codoped sample was improved, and the light output value at 175°C was 36,000 photons/MeV, which was 93% of that at 25°C.

DOI： 10.1016/j.optmat.2017.02.062

Scopus

出版者・発行元：Journal of Materials Science  

Li-containing materials can be applied as neutron scintillators, and LiBaF<inf>3</inf> can discriminate neutron and gamma rays. Moreover, LIF/LiBaF<inf>3</inf> can have higher cross section of thermal-neutron capture compared with LiBaF<inf>3</inf>. In this study, LiF (82.5 mol%) and (Ba<inf>1−x</inf> RE<inf>x</inf>)F<inf>2</inf> (17.5 mol%, RE = Ce and Eu, x = 0.002) eutectic crystals, LiF/RE:LiBaF<inf>3</inf>, were grown by the micropulling down method with different pulling rates (growth rate) in order to observe the eutectic structure. Lamellar microstructure was formed for each pulling rate. LiF/Ce:LiBaF<inf>3</inf> excited by 5.5-MeV alpha rays had a broad peak at ~350 nm corresponding to 5d–4f transition of Ce³⁺. On the other hand, LiF/Eu:LiBaF<inf>3</inf> had two scintillation processes; a sharp emission was originated from ⁶P<inf>7/2</inf> → ⁸S<inf>7/2</inf> transitions in the 4f electronic configuration of Eu²⁺ at 360 nm, and a broad one was attributed to Eu²⁺ trapped exciton recombination at 400–450 nm. Since scintillation light was observed for these materials, these scintillators are sensitive to neutrons.

DOI： 10.1007/s10853-017-0815-1

Scopus

出版者・発行元：Optical Materials  

The In-doped LiCaAlF<inf>6</inf> [In:LiCAF] single crystals were grown by the micro-pulling-down (μ-PD) method, and the phases, chemical compositions, transmittance and radioluminescence spectra were investigated. All the grown crystals showed high transparency and single phase of LiCAF without visible cracks and inclusions except for the end part of In2%:LiCAF crystal which included the impurity phase. In the radioluminescence spectra of the In:LiCAF crystals under X-ray irradiation, the emission peak around 750 nm was revealed.

DOI： 10.1016/j.optmat.2016.10.040

Scopus

出版者・発行元：Optical Materials  

(Ce<inf>0.01</inf> Gd<inf>0.59</inf> La<inf>0.40</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystal (La40% sample) was grown by the micro-pulling-down method to study its scintillation properties and their temperature dependence. In addition, we investigated the relation between these properties and La concentration comparing the crystal with (Ce<inf>0.01</inf> Gd<inf>0.90</inf> La<inf>0.09</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (La9% sample). As results, the light output of the La40% sample at 25°C was similar to that of the La9% sample. On the other hand, the decay time of the La40% sample was slower than that of the La9% sample at 25°C. The light output of La40% sample had a small decrease rate at high temperature when compared with that of La9% sample.

DOI： 10.1016/j.optmat.2016.10.039

Scopus

出版者・発行元：Iop Conference Series Materials Science and Engineering  

Nonstoichiometric Lu<inf>3</inf>Al<inf>5+x</inf>O<inf>12</inf> (x= 0.05, 0.15, 0.35, 0, -0.05, -0.15, -0.35) crystals were grown by the μ-PD method. Luminescence and scintillation properties such as absorption, excitation and emission spectra, light yield and decay time were evaluated. Expected anti-site defect related host emission have been observed in 250-420nm. Emission intensity was increased by increasing the nonstochiometry. The x=-0.35 sample showed the highest light yield of around 12000 photons/MeV and slowest scintillation decay time of 1.96μs.

DOI： 10.1088/1757-899X/169/1/012013

Open Access

Scopus

出版者・発行元：Journal of Instrumentation  

Optical and scintillation properties of pure Cs<inf>2</inf>HfCl<inf>6</inf> (CHC) single crystals were investigated. In particular, light output and energy resolution were measured using a Si avalanche photodiode (Si-APD), since the Si-APD has sufficient quantum efficiency of around 70 % at emission wavelength region of CHC around 420 nm. This CHC single crystal grown using the vertical Bridgeman method showed light output of 37,000andplusmn; 2,000 photons/MeV . The FWHM energy resolution was determined to be 3.7andplusmn; 0.5andtimes; (E/662 keV)^{-0.85andplusmn; 0.03}[%], where E [keV] is the gamma-ray energy. Moreover, the temperature dependence of the light output was stable from -5 to 30 ^-C, while the light output increased below -10 ^-C.

DOI： 10.1088/1748-0221/12/02/C02042

Scopus

出版者・発行元：Optics Infobase Conference Papers  

We report on distribution of Eu ions doped CaF2 single crystal by measurement of multi-photon luminescence. Distribution of Eu²⁺ and Eu³⁺ ions is measured respectively because the luminescence peak due to Eu²⁺ and Eu³⁺ ions is different. We observed the difference in distribution of Eu²⁺ and Eu³⁺ ions doped CaF2 which is grown by Annealing method and micro pulling-down method.

Scopus

出版者・発行元：IEEE International Ultrasonics Symposium Ius  

Acoustic properties for Ca<inf>3</inf>Nb(Ga<inf>1-x</inf>Al<inf>x</inf>)<inf>3</inf>Si<inf>2</inf>O<inf>14</inf> [CNGAS(x)] single crystals were experimentally investigated as a function of Al substitution content. Several plate specimens of the X-, Y-, Z-, 40°Y-, and 145°Y-cut were prepared from CNGAS(x) single crystal ingots (x=0, 0.25, and 0.50) grown by Czochralski technique. Velocities of longitudinal wave, shear wave, and leaky surface acoustic wave (LSAW) were measured for the CNGAS(x) specimens at 23°C using the ultrasonic microspectroscopy (UMS) system. Densities were also measured. It was experimentally demonstrated that all of acoustic properties were linearly changed as a function of Al substitution content.

DOI： 10.1109/ULTSYM.2016.7728806

Scopus

出版者・発行元：Optical Materials  

Tb-doped LiGdF<inf>4</inf>-LiF eutectics were grown at various growth rate and their directionally solidified eutectic (DSE) system has been investigated. Well aligned fiber like eutectic structure with around 1.7 μm in diameter and 1200 μm in maximum length was obtained the growth speed of 0.15 mm/min. The sample showed optical transparency like bundle optical fibers and around 40% of transmittance at 1.5 mm thick was achieved in 380–630 nm range. The expected 380–630 nm emission exited by UV and α-ray, and 270–330 nm excitation of Tb³⁺⁸S -⁶P transition have been observed. The weak emission of Gd³⁺ 4f-4f transition at 310 nm was also observed under alpha-ray excitation. The Observed excitation bands peaking at around 275 nm and 310 nm correspond respectively to the ⁸S^7/2- ⁶I<inf>7/2</inf> and ⁸S<inf>7/2</inf>-⁶P<inf>J</inf> absorption bands of Gd³⁺.

DOI： 10.1016/j.optmat.2016.09.019

Scopus

出版者・発行元：Journal of Crystal Growth  

Cr-doped (Gd<inf>x</inf>Y<inf>1−x</inf>)<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> crystals (x=0.00, 0.25, 0.50, 0.75 and 1.00) were grown by the micro-pulling-down method and examined for their possible application as red and infrared scintillating detectors in medical field. Although Cr:(Gd<inf>0.75</inf>Y<inf>0.25</inf>)<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> and Cr:Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> had similar X-ray diffraction patterns, other samples showed some change in lattice constant. All the crystals had broad emission bands in the red and infrared region when excited by either 450 nm photons or X rays. These bands were associated with ⁴T<inf>2</inf>→A<inf>2</inf> transitions. Moreover, redshift of the emission-peak wavelengths (⁴T<inf>2</inf>→⁴A<inf>2</inf>) and absorption peaks (⁴A<inf>2</inf>→⁴T<inf>1</inf> and ⁴T<inf>2</inf>) was observed with increase of Gd content (x) in Cr-doped (Gd<inf>x</inf>Y<inf>1−x</inf>)<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> due to the change of the crystal fields. The crystals had scintillation emissions in the wavelength region suitable for the real time dose monitoring in radiation therapy.

DOI： 10.1016/j.jcrysgro.2016.02.004

Scopus

出版者・発行元：Optical Materials  

(Ce<inf>x</inf>Yb<inf>1-x</inf>)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> (x = 0.00, 0.01) single crystals were grown by the micro-pulling-down method to test the possibility of its application as infra-red scintillator for medical imaging. Powder X-ray diffraction analysis indicated that the crystals were single-phase materials. The radioluminescence spectra of the crystals demonstrated presence of two near infra-red emission peaks (at 1010 and 1030 nm). The emission peaks at 420 and 580 nm ascribed to defects were also observed in the crystals. The human body has maximum transmission in wavelength range from 650 to 1200 nm. Therefore, Yb<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> is expected to be used as efficient infra-red scintillator for medical applications.

DOI： 10.1016/j.optmat.2016.04.032

Scopus

出版者・発行元：Journal of Rare Earths  

HfO<inf>2</inf>/α-Al<inf>2</inf>O<inf>3</inf> eutectics were grown by the micro-pulling down (μ-PD) method at the composition of 63.2 mol.% α-Al<inf>2</inf>O<inf>3</inf>, 35.512 mol.% HfO<inf>2</inf>, 0.92 mol.% Eu<inf>2</inf>O<inf>3</inf> and 0.368 mol.% Y<inf>2</inf>O<inf>3</inf>. Rod phases with around 3–4 μm diameter were observed on the transverse cross-section. The phase-separated scintillator fibers (PSSFs) structure with fibers of around 3–4 μm diameter and 10–20 μm length was observed. The electron back scattering patterns indicated crystal orientation of [101] for monoclinic HfO<inf>2</inf> rod phase and [0001] for α-Al<inf>2</inf>O<inf>3</inf> matrix in the transverse cross-section. Eu³⁺ 4f-4f emission was observed at 550–750 nm.

DOI： 10.1016/S1002-0721(16)60096-0

Scopus

出版者・発行元：Radiation Measurements  

The ns²-type metal elements (Pb and Sn) doped LiCaAlF<inf>6</inf> single crystals were grown by a micro-pulling-down (μ-PD) method. Pb doped LiCaAlF<inf>6</inf> [Pb:LiCAF] crystals showed high transparency and single phase of the LiCAF structure. However, we could not obtain Sn:LiCAF crystals due to the evaporation of SnF<inf>2</inf> during the crystal growth. There was an absorption peak around 193 nm in the transmittance spectrum of Pb:LiCAF crystal. In the radioluminescence spectrum of the Pb:LiCAF crystal under X-ray irradiation, two emission peaks around 200 and 830 nm were observed.

DOI： 10.1016/j.radmeas.2016.02.021

Scopus

出版者・発行元：Radiation Measurements  

1300 or 1400 °C pre–sintered Al/Ce/Mg:SrHfO<inf>3</inf> and Al/Ce:SrHfO<inf>3</inf> ceramics were prepared by the Spark Plasma Sintering (SPS) in order to search for a new scintillation material with a high–effective atomic number(Z<inf>eff</inf>) and good light output. The SrHfO<inf>3</inf> has a high Z<inf>eff</inf> of 60, and high gamma–ray detection efficiency is expected. Meanwhile it has a high melting point of over 2500 °C, and single crystal is hard to be grown. On the other hand, high melting materials can be prepared as ceramics, and the SPS method is a simple process to fabricate the ceramics within a few hours. Thus, we prepared the samples using the SPS method, and their optical and scintillation properties were investigated. We found that Al/Ce/Mg:SrHfO<inf>3</inf> and Al/Ce:SrHfO<inf>3</inf> ceramics had an emission wavelength at around 400 nm originating from 5d–4f transition of Ce³⁺. Moreover, Al/Ce/Mg:SrHfO<inf>3</inf> pre-sintered at a temperature of 1400 °C had a light output of approximately 5,000 ph/MeV. In this paper, the light output of Mg-co-doped samples was improved compared with the Mg-free ones. The light output also depends on the pre-sintering temperature.

DOI： 10.1016/j.radmeas.2016.02.025

Scopus

出版者・発行元：Applied Physics Express  

From measuring absorption spectra of cerium-doped Gd<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> (Ce:GAGG) and undoped GAGG crystals at low temperatures under UV-light irradiation, we find that they exhibit a broad band at around 12000 cm%1. This band is enhanced by high-temperature annealing under a hydrogen atmosphere. On the basis of present experimental results, the UV-induced band is assigned to shallow electron traps of defect complexes associated with oxygen vacancies. The UV-induced band completely disappears with Mg2+ codoping. We conclude that the Mg2+ codoping has the effect of inhibiting the formation of shallow electron traps, which realizes a faster scintillation response of Ce:GAGG.

DOI： 10.7567/APEX.9.072602

Scopus

出版者・発行元：Optical Materials  

Ce-doped lutetium aluminum garnet Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (LuAG) nanoceramics were fabricated at 1600°C and 1700°C by spark-plasma sintering (SPS) method from nano-powders prepared by radiation synthesis. Both undoped and Ce-doped LuAG ceramic samples were also prepared from the nano-powders at 1700°C with significantly increased pre-heating rate. The backscattered electron images revealed large amount of pores in all the Ce-doped samples causing their significant opacity. On the other hand, very large grains and no pores were revealed in the undoped sample, which was the only transparent one. The radioluminescence measurements revealed superior overall scintillation efficiency of the samples sintered at the temperature 1700°C, and their defect emission in the UV region was ascribed to oxygen-vacancy-related defects such as F⁺ centers. The photoluminescence decay of the defect emission was characterized by an extremely fast decay time of a few nanoseconds. Influence of sintering procedure and subsequent annealing on the luminescence and scintillation properties is discussed.

DOI： 10.1016/j.optmat.2016.01.024

Scopus

出版者・発行元：Proceedings of International Symposium on Radiation Detectors and their Uses Isrd 2016  

Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator has a high light output, fast decay time, and it has been expected to be applied in various fields. One of the applications is to use in the space for astronomy, and therefore, the evaluation of the radiation hardness is required. We grew a Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> single crystal by the Czochralski technique, and evaluated its radiation hardness using 80-MeV alpha rays in Tohoku University with a total dose of approximately 20,000 Gy. The light outputs and decay times were slightly degraded after the irradiation by few %. Only the energy resolution was degraded dramatically in the 80-MeV alpha-ray range, and Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator was found to have good radiation hardness for alpha rays.

DOI： 10.7566/JPSCP.11.020002

Open Access

Scopus

出版者・発行元：Optics Infobase Conference Papers  

Scopus

出版者・発行元：Proceedings of International Symposium on Radiation Detectors and their Uses Isrd 2016  

Since Ce-doped (Gd, La)<inf>2</inf>Si<inf>2</inf>O<inf>7</inf> scintillator was reported to have high light output, fast decay time and good temperature stability of the scintillation properties, it was expected to find application in various fields. In this study, we evaluated Zr codoping effect by measuring temperature dependence of photoluminescence and scintillation characteristics. The single crystals were grown by Czochralski technique and the light output at 448 K was around 80% of that at 298 K.

DOI： 10.7566/JPSCP.11.020007

Open Access

Scopus

出版者・発行元：Optical Materials  

Eu doped BaCl<inf>2</inf>/LiF eutectics were grown by the micro-pulling down method and their directionally solidified eutectic (DSE) system has been investigated. The grown eutectic showed main phases of cubic LiF and orthorhombic BaCl<inf>2</inf>. In these eutectics, the 399 nm emission of Eu²⁺ 4f5d was obtained. It shows the intrinsic decay time of about 410 ns. The light yield of the 1-mm-thick eutectic showed 7000 ph/5.5 MeV alpha-ray.

DOI： 10.1016/j.optmat.2015.09.028

Scopus

出版者・発行元：Japanese Journal of Applied Physics  

LiF/CaF<inf>2</inf>/LiBaF<inf>3</inf> ternary eutectic scintillators were grown by the μ-PD method. In the solidified eutectic the phases were uniformly distributed in the transverse direction and aligned along the growth direction. For the Eu-doped samples, the expected emission peak observed at 425nm was ascribed to Eu²⁺ 5d-4f transition from Eu:CaF<inf>2</inf> under X-ray excitation. The LiF/CaF<inf>2</inf>/LiBaF<inf>3</inf> ternary eutectic scintillators showed a light yield around 7,000 photons/neutron and decay time of 260 ns (73.6%) and 50 ns (26.4%).

DOI： 10.7567/JJAP.54.04DH04

Scopus

出版者・発行元：Optical Materials  

Nd 1 mol% doped (Lu, Gd)<inf>3</inf>(Ga, Al)<inf>5</inf>O<inf>12</inf> (LGGAG) single crystals were grown by the micro-pulling down (μ-PD) method. Luminescence and scintillation properties such as absorption, excitation and emission spectra, light yield and decay time were evaluated. Nd1%:Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> showed the highest light output of around 8200 photons/MeV among the grown crystals. Scintillation decay time of Nd:Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> was 1.32 μs (36%) 2.02 μs (64%). Nd:Lu<inf>3</inf>Ga<inf>3</inf>Al<inf>2</inf>O<inf>12</inf> was relatively high dense scintillator of 7.38 g/cm³ with good light yield of 6800 photons/MeV and scintillation decay time of 0.20 μs (5%) 2.60 μs (95%).

DOI： 10.1016/j.optmat.2014.10.007

Scopus

出版者・発行元：Radiation Measurements  

Luminescence and scintillation properties of Eu-doped 75⁶LiF-12.5AlF<inf>3</inf>-12.5CaF<inf>2</inf> eutectics suitable for thermal neutron detection are reported. The 0.5 and 1.0% Eu-doped eutectics were grown by micro-pulling down (μ-PD) technique. These materials demonstrated two emission bands with maximums at 375 and 430 nm wavelengths under excitation with 250-400 nm wavelength radiation. The emission band at 375 nmwas associated with 4f⁶5d-4f⁷(⁸S<inf>7/2</inf>) transition of Eu²⁺ in the CaF<inf>2</inf> phase, and the 430 nm band could be result of incorporation of Eu²⁺ into Li<inf>3</inf>AlF<inf>6</inf> and other phases. When alpha-ray excited the eutectics, both Eu²⁺ 4f⁶5d-4f⁷(⁸S<inf>7/2</inf>) and Eu³⁺ 4f⁶-4f⁶ (⁵D<inf>0</inf>-⁷F<inf>1, 2</inf>) emission band were detected at 430 nm and 590 nm. The scintillation decay time of the eutectics were determined to be about 540 ns for Eu 0.5% and 380 ns for Eu 1.0%, respectively. According to pulse height spectra registered under ²⁵²Cf irradiation, the relative scintillation light yield of the eutectics was observed to be 6000 ph/n (Eu 0.5%) and 2000 ph/ n (Eu 1.0%) when compared to ⁶Li-loaded glass commercial scintillator.

DOI： 10.1016/j.radmeas.2014.06.007

Scopus

出版者・発行元：Optical Materials  

Sr co-doped Ce:LiCaAlF<inf>6</inf> [Ce:Li(Ca,Sr)AlF<inf>6</inf>] crystals with various Ca/Sr ratios were grown by a micro-pulling-down (μ-PD) method and effects of Sr co-doping on crystal structure, chemical composition, optical and scintillation properties for Ce:LiCaAlF<inf>6</inf> crystals were investigated as a neutron scintillator. High transparent Ce2%:Li(Ca,Sr)AlF <inf>6</inf> crystals with 2% and 5% Sr contents were obtained while Ce2%:Li(Ca,Sr)AlF<inf>6</inf> crystals with 10% and 20% Sr contents included milky parts in the crystals. a- and c-axis lengths of Ce:Li(Ca,Sr)AlF <inf>6</inf> phase systematically increased with an increase of Sr content. In addition to the emission at 284 and 308 nm from Ce³⁺ ion, emission peaks at 367 nm appeared by Sr co-doping. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2014.02.025

Scopus

出版者・発行元：Optical Materials  

Eu doped LiSrAlF<inf>6</inf> (Eu:LiSAF) crystals with various Eu concentrations were grown by a micro-pulling-down (μ-PD) method and the effects of Eu concentration control on crystal growth and scintillation properties for Eu:LiSAF crystals were investigated as a neutron scintillator. As-grown Eu0.3%:LiSAF crystal had no visible inclusion while milky parts were observed in the crystals with higher Eu contents. The secondary phases with the chemical composition of EuF<inf>2</inf> or EuF<inf>3</inf> in the Eu:LiSAF matrix were observed for the crystals with high Eu contents while the secondary phase couldn't be observed in the powder XRD patterns. In the radioluminescence spectra of Eu:LiSAF crystals under α-ray irradiation, emission peaks around 375 nm originated from 5d-4f transition of Eu²⁺ ion were observed. The light yields systematically increased with an increase of actual Eu contents in the crystals and the decay times were 1490-1620 ns. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2014.02.007

Scopus

出版者・発行元：Optical Materials  

Cr-doped (Gd<inf>X</inf> Y<inf>1-X</inf>) <inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (X = 0, 0.25, 0.50) crystals prepared by the micro-pulling down method were investigated to develop a infra-red scintillator for implantable patient dosimeter in radiation therapy. In order to evaluate their optical and scintillation performance, the following properties were measured: (i) transmittance between ultra-violet and near-infra red region, (ii) photoluminescence spectra under Xe-lamp excitation, and (iii) X-ray excited radio-luminescence spectra. Cr:Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> and Cr:(Gd<inf>0.25</inf> Y<inf>0.75</inf>)<inf>3</inf>Al<inf>5</inf>O <inf>12</inf> crystals showed increased transmittance of 80%, while Cr:(Gd <inf>0.50</inf> Y<inf>0.50</inf>)<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> had a lower transmittance of 40% due to its polycrystalline structure. In addition, all the Cr:(Gd<inf>X</inf> Y<inf>1-X</inf>)<inf>3</inf>Al <inf>5</inf>O<inf>12</inf> crystals showed sharp scintillation luminescence peaks ascribed to Cr³⁺ d-d transitions. Therefore, these results suggested that Cr:Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> and Cr:(Gd <inf>0.25</inf> Y<inf>0.75</inf>)<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> crystals can be candidate materials for the dosimeter use. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2014.04.002

Scopus

出版者・発行元：Journal of Crystal Growth  

Single crystals of orthorhombic and monoclinic BaLu<inf>2</inf>F<inf>8</inf>doped with Nd and Tm were grown by micro-pulling-down method. The monoclinic (low temperature modification) was grown using LiF flux, while the orthorhombic (high temperature modification) was grown with special hot-zone with shallow gradient and employing quenching process. Reasonable scintillation efficiency was achieved for the crystals of the former modification, while no rare-earth ion emission was observed in the latter due to preferential energy transfer to defects. The orthorhombic (low temperature) modification of ErF<inf>3</inf>was grown using LiF flux and hot zone with steep gradient. Quite low scintillation efficiency was found for the Nd-doped sample due to energy migration over the Er³⁺levels. Possibility of using pure ErF<inf>3</inf>as an infra-red scintillator is discussed.

DOI： 10.1016/j.jcrysgro.2013.12.040

Scopus

出版者・発行元：Journal of the European Ceramic Society  

Neutron imaging devices employing a scintillator can be used in various fields, and eutectic crystals can be suitable for the imaging with a fine position resolution of a few hundred micrometers. Since LiF and LaF<inf>3</inf> have different refractive indexes of 1.41 and 1.64 at 300nm, respectively, the eutectic crystal is expected to behave as a scintillator with light guiding properties. Thus, the optical properties of Ce-doped LiF/LaF<inf>3</inf> eutectic crystal grown by micro-pulling down method were investigated. The light output of LiF/Ce:LaF<inf>3</inf> eutectic crystal was relatively small. The emission peaks at 300nm originating from Ce³⁺ of 5d-4f transition were observed under excitation by UV photons and 5.5MeV alpha rays. Moreover, the photo-luminescence decay time of Ce-doped LiF/LaF<inf>3</inf> eutectic crystal was estimated to be 17±1ns. © 2014 Elsevier Ltd.

DOI： 10.1016/j.jeurceramsoc.2014.01.037

Scopus

出版者・発行元：Optical Materials  

1-mol%-Yb-doped Gd<inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> infra-red scintillator crystal has been studied as a novel implantable radiation monitor in radiation therapy. Powder X-ray diffraction measurement and chemical analysis with a field emission scanning microscope and wavelength dispersive spectrometer determined its garnet structure and average chemical composition of Yb<inf>0.03±0.01</inf>Gd<inf>2.99±0.07</inf>Al <inf>2.21±0.08</inf>Ga<inf>2.64±0.09</inf>O <inf>12.10±0.09</inf>. Transmittance measurements reached high values of approximately 70% in the human body transparency region between 650 to 1200 nm. Photoluminescence peaks were detected around 970 and 1030 nm under the 940 nm excitation with a Xe lamp. Infra-red scintillation emissions were clearly observed around 970 and 1030 nm due to Yb³⁺ 4f-4f transitions under X-ray excitation. Therefore, these results suggest that Yb-doped Gd <inf>3</inf>Al<inf>2</inf>Ga<inf>3</inf>O<inf>12</inf> might be used as an infra-red scintillator material. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2014.04.007

Scopus

出版者・発行元：Journal of Crystal Growth  

Nd and Yb doped CaYAlO<inf>4</inf> crystals have been grown by the micro-pulling down method. The segregation coefficient along the growth direction and the radial dopant distribution were measured by using electron probe micro-analysis (EPMA). The X-ray induced luminescence spectra in the spectral range from 300 to 1500 nm were measured: Nd and Yb doped CaYAlO <inf>4</inf> showed intense peaks at 990 and 1045 nm, respectively. These crystals would be promising materials for near infrared emission scintillators. © 2013 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2013.11.089

Scopus

出版者・発行元：Journal of Crystal Growth  

We have investigated the optical properties of 1 mol% Nd-doped SrBr <inf>2</inf> crystal grown by the Bridgman technique for an X-ray scintillator application. We succeeded in obtaining a transparent crystal, whose X-ray diffraction was measured under dry condition because of its hygroscopic nature. Roughly, we estimated that 90% of this crystal dissolved within 300 min. under 25 °C and 65-70% humidity. Under excitation by 270 and 400 nm photons several emission peaks originating from ⁴F<inf>3/2</inf> or ⁴G<inf>i1</inf>→⁴I<inf>i2</inf> (i1=5/2 and 7/2 and i2=13/2, 11/2, and 9/2) transitions of Nd³⁺ were observed. 1 mol% Nd:SrBr<inf>2</inf> had a maximum quantum yield of approximately 45%. Additional emission peaks were observed under X-ray excitation. © 2013 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2013.11.082

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

We evaluated optical and scintillation properties of a 0.03% Cr-doped Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (GGG:Cr) single crystal grown by Czochralsk method for medical use. Since human body has low absorption region from approximately 700-1100 nm, near infrared scintillators would be applied to the real time dose monitor system. In the X-ray excited radioluminescence, the emissions related to ²E→⁴ A<inf>2</inf> transitions of Cr³⁺ were observed at around 725 nm. The scintillation light yield of GGG: Cr 0.03% single crystal under 5.5 MeV alpha-ray excitation was determined to be 30% of BGO. © 2014 IEEE.

DOI： 10.1109/TNS.2013.2290550

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Nd³⁺ -doped Lu<inf>2</inf>O<inf>3</inf> (Nd: Lu <inf>2</inf>O<inf>3</inf>) is a candidate for an infrared scintillator because (i) Lu<inf>2</inf>O<inf>3</inf> has a high density of 9.5g/cm³ and a high atomic number of 67 and (ii) Nd³⁺-doped materials emit in the infrared range and the emission lines from Nd³⁺ can be used in medical applications since human body has a transparency window between 600 and 1,100 nm. However, it is extremely difficult to fabricate Lu<inf>2</inf>O <inf>3</inf> single crystals using conventional crystal growth methods because of the high melting point (2,510 °C). Using solid-state reactions, it is much easier to fabricate Lu<inf>2</inf>O<inf>3</inf> into a ceramic structure. Therefore, Nd: Lu<inf>2</inf>O<inf>3</inf> transparent ceramics were fabricated using a spark plasma sintering method. This technique is comparatively simple and consumes less time than other methods such as vacuum hot pressing. The scintillation properties and transmittance spectra of the as-produced ceramics were studied in both the visible and infrared regions. Radioluminescence spectra were measured in the range 800-1,200 nm. Nd³⁺ emission lines were observed in the transparency window of human body. Thus, these ceramic materials could be a candidate for medical imaging applications. © 2014 IEEE.

DOI： 10.1109/TNS.2013.2290554

Scopus

出版者・発行元：Key Engineering Materials  

Ce and Ca co-doped LiGdF4-LiF eutectics were grown and their directionally solidified eutectic (DSE) system has been investigated. In these eutectics, apart from the expected 305 nm emission of the regular Ce³⁺, 310 nm emission of the Gd³⁺ and Ce³⁺ -perturbed emission around 320-380 nm was observed. Ce³⁺-perturbed emission at 340 nm shows the intrinsic decay time of about 27 ns. In photoluminescence mechanism the observed decay time shortening of the regular Ce³⁺ and Gd³⁺ centers point to the energy transfer in the sequence the regular Ce ³⁺?→ (Gd³⁺)<inf>n</inf>?→ the perturbed Ce ³⁺ sites. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.616.96

Open Access

Scopus

出版者・発行元：Key Engineering Materials  

We evaluated optical and scintillation properties of a Cr 0.5%:Y <inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (YGG) and Cr 0.5%:Y<inf>3</inf>Al <inf>5</inf>O<inf>12</inf> (YAG) crystals grown by the micro-pulling down method for infrared emission scintillators. In the photoluminescence and X-ray induced radioluminescence measurements, the emissions peaks of Cr:YGG were located in the longer wavelength than those of Cr:YAG. Radioluminescene spectrum of Cr:YGG had a broad peak at 716 nm related to Cr³⁺ ²E→ ⁴A<inf>2</inf> and ⁴T→⁴A<inf>2</inf> transitions. © (2014) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.616.92

Open Access

Scopus

出版者・発行元：Optical Materials  

Multicomponent garnet Ce:Gd<inf>3</inf>(Ga,Al)<inf>5</inf>O<inf>12</inf> (Ce:GAGG) single crystals show very high light yield with reasonably fast scintillation response. Therefore, they can be promising scintillators for gamma-ray detection. However, in the decay curve a very slow component does exist. Therefore, it is necessary to optimize further the crystal growth technology of Ce:GAGG. In this study, Ce:GAGG single crystals were grown by the floating zone (FZ) method under atmospheres of various compositions such as Ar 100%, Ar 80% + O<inf>2</inf> 20%, Ar 60% + O<inf>2</inf> 40% and O<inf>2</inf> 100%. Radioluminescence spectra are dominated by the band at about 540 nm due to Ce³⁺ 5d<inf>1</inf>-4f transition. The Ce:GAGG single crystal grown under Ar atmosphere shows an intense slower decay component. It can be related to the processes of the delayed radiative recombination and thermally induced ionization of 5d<inf>1</inf> level of Ce³⁺ center possibly further affected by oxygen vacancies. This slower decay process is significantly suppressed in the samples grown under the O<inf>2</inf> containing atmosphere. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2013.02.021

Scopus

出版者・発行元：Optical Materials  

Nd-doped LuLiF<inf>4</inf> single crystalline scintillators with different Nd concentrations of 1%, 2%, 3%, and 4% were grown by the micro-pulling-down (μ-PD) method and that of Nd 1% were grown by the Czochralski method. There are some absorption bands due to Nd³⁺ 4f-4f transitions in the spectra and these lines correspond to the transitions from the ground state ⁴I<inf>9/2</inf> to the excited states. In photo- and radio-luminescence spectra, Nd³⁺ 4f-4f transition peaks were observed. The photoluminescence decay time for ⁴D<inf>3/2</inf> → ⁴I<inf>13/2</inf> transition showed approximately 0.75 μs and slow component. The highest light yield was estimated to be 700 photon/MeV for LuLiF<inf>4</inf>:Nd2% crystal grown by the μ-PD method. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2013.02.010

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

Time-of-flight Positron emission tomography (TOF-PET) is one of the next-generation medical imaging methods, which requires scintillators with a very short decay time. However, the shortest scintillation decay times are typically 20-30 ns, and these values are not sufficient for TOF-PET. Cherenkov counters are used in high energy physics and they are expected to be applied in medical imaging due to their short decay time. Here, high-refractive index materials are necessary for Cherenkov radiators to reach a high light output. We measured refractive indices of Gd<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (GGG), Y<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (YGG) and Lu<inf>3</inf>Ga <inf>5</inf>O<inf>12</inf> (LuGG) crystals grown by a micro-pulling-down (μ-PD) method. The GGG, YGG and LuGG crystals were found to have refractive indices of ~2.5, ~2.3 and ~2.3 at 400 nm, respectively. Then we grew a 40 mm diameter GGG crystal by the Czochralski method, and the emission decay times of the GGG crystals irradiated with muons and gamma rays were 10±1ns and 10±2ns, respectively, using a photomultiplier tube (Hamamatsu R6231-100). Cherenkov light of the GGG crystal could be observed for the gamma-ray irradiation. © 2013 Elsevier B.V.

DOI： 10.1016/j.nima.2013.08.018

Scopus

出版者・発行元：Radiation Measurements  

Eu and Rb co-doped LiCaAlF<inf>6</inf> (LiCAF) single crystals with different dopant concentrations were grown by the micro-pulling-down method for neutron detection. Their transmittance spectra showed strong absorption bands at 200-220 and 290-350 nm, and under ²⁴¹Am alpha-ray excitation, their radioluminescence spectra exhibited an intense emission peak at 373 nm that was attributed to the Eu²⁺ 5d-4f transition. These results were consistent with those for the Rb-free Eu:LiCAF. The highest light yield among the grown crystals was 36,000 ph/n, which was 20% greater than that of the Rb-free crystal. In addition, the neutron-excited scintillation decay times were 650-750 ns slower than that of the Rb-free Eu:LiCAF. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.radmeas.2013.04.021

Scopus

出版者・発行元：Radiation Measurements  

Capability of thermal neutron detection was examined for LiCaAlF <inf>6</inf> (LiCAF) scintillators doped with 3d-transition metal ions. Their radioluminescence spectra were measured with an 241-Am source to simulate ⁶Li(n, α)³H reaction. The sufficiently intense radioluminescence was observed for the Mn, Co and Cu dopants, while only a weak one was observed for Ti, V, Fe and Ni. A Mn doped LiCAF crystal, which showed the highest radioluminescence intensity, was coupled with a Si avalanche photodiode for the examination of its neutron response. It was confirmed that the average current of the photodiode clearly increased under excitation with 13.5 meV neutron flux. © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.radmeas.2013.03.024

Scopus

出版者・発行元：Radiation Measurements  

In photoluminescence which directly excites the emission center of phosphor material is known to have a correlation between the emission wavelength and the decay time based on quantum mechanics. In scintillation phenomenon, host lattice of the material is first excited by ionizing radiation and then the excitation energy is transferred to emission centers. For the first time, we investigated the correlation between the scintillation decay and the emission wavelength by using pulse X-ray equipped streak camera system which could observe time and wavelength resolved scintillation phenomenon. Investigated materials were Ce³⁺, Pr³⁺ and Nd³⁺ doped oxides and fluorides which all showed 5d-4f transition based emission. As a result, we obtained the relation that τ (scintillation decay time) was proportional to the λ^2.15 (emission wavelength). © 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.radmeas.2012.05.014

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Ce 0.1, 0.5, 1.0, and 2.0 mol%-doped K<inf>2</inf>NaLuF<inf>6</inf> crystals with 2 mm in diameter and 30-50 mm in length were grown by micro-pulling-down method. The photoluminescence spectra under ultraviolet excitation showed intense emission ascribed to 5d-4f transitions of Ce ³⁺ replacing Lu³⁺ isolated octahedral site. In the radioluminescenced spectra under alpha-ray irradiation, the emission band is due to the transition from the lowest 5d excited state of Ce³⁺ to 2F<inf>5/2</inf> ground state level is dominant. The light yields of Ce:K <inf>2</inf>NaLuF}<inf>6</inf> under 5.5-MeV alpha-ray excitation was estimated to be approximately 1.2 to 1.8% of those of BGO. © 1963-2012 IEEE.

DOI： 10.1109/TNS.2013.2247061

Scopus

出版者・発行元：Radiation Measurements  

Er-doped Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> single crystals with different Er concentrations of 0.1, 1.0, 10, 30, and 50% were grown by the micro-pulling down method. There were several absorption lines due to the Er³⁺ 4f-4f transitions in the transmittance spectra and these lines correspond to the transitions from the ground state of ⁴I <inf>15/2</inf> to the excited states. The photo- and radio-luminescence spectra showed Er³⁺ 4f-4f emissions. Relative light yield under 5.5 MeV alpha-ray irradiation of Er 0.1%:Y<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> was estimated to be 63% of that of Bi<inf>4</inf>Ge<inf>3</inf>O<inf>12</inf>. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.radmeas.2013.01.056

Scopus

出版者・発行元：Optical Materials  

1, 3, and 6 mol% Nd³⁺ doped (YGd<inf>2</inf>)(Sc <inf>2</inf>Al<inf>2</inf>Ga)O<inf>12</inf> transparent ceramic garnets were fabricated by the sintering to investigate their optical and scintillation properties. They were all visibly purplish and exhibited 80% transparency in wavelength longer than 300 nm with several absorption bands due to Nd ³⁺ and Gd³⁺ 4f-4f transitions. In photo- and radio-luminescence spectra, they showed intense emission peaks at 383 and 416 nm. Photoluminescence decay time of the former resulted ∼500 μs and those of the latter 400 and 900 ns, respectively. Scintillation light yield was examined by using ²⁴¹Am 5.5 MeV α-ray and the light yield resulted ∼200 photons/5.5 MeV α in Nd 1 mol% doped sample. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2012.05.034

Scopus

出版者・発行元：Journal of Crystal Growth  

The Nd-doped Lu<inf>3</inf>Al<inf>5</inf>O<inf>12</inf> (Nd:LuAG) single crystal was grown by the Czochralski (CZ) method. In XRC profiles, the full-width at half-maximum (FWHM) value was 58 arcsec, which was much higher than that of the μ-PD (194 arcsec). In photo and radio-luminescence spectra, the CZ grown sample showed strong emission peaks attributed to Nd³⁺ 4f-4f transitions in visible wavelengths longer than 400 nm. The Nd:LuAG grown with the CZ method showed light yield of 7900 photons/MeV, which is comparable with the standard BGO and energy resolution of 14% under ¹³⁷Cs γ-ray excitation. © 2011 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2011.10.030

Scopus

出版者・発行元：Journal of Crystal Growth  

Lu co-doped Ce:LiYF<inf>4</inf> single crystals with Lu 0, 25, 50, 75 and 100 at% concentrations were grown for the control of mean ionic radius at Y site and the effects on crystal growth, structural phase, crystallinity and segregation were investigated. Lu co-doped Ce 2 at%:LiYF<inf>4</inf> single crystals with Lu 0, 25, 50, 75 and 100 at% concentrations were grown by the micro-pulling-down method and while the initial part of Ce:LiYF<inf>4</inf> single crystal indicated opaque and milky due to the increase of mean ionic radius at Y site by Ce³⁺ doping, Lu co-doped crystals had transparency in all part of crystals. All Lu co-doped crystals indicated a single phase in XRD measurements and the lattice parameters were systematically decreased with an increase in Lu concentration. Crystallinity of grown crystals became worse by Lu co-doping and the effective segregation coefficients of Ce³⁺ ion for Lu co-doped crystals were almost the same, 0.15-0.19. © 2011 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2011.11.020

Scopus

出版者・発行元：Physica Status Solidi C Current Topics in Solid State Physics  

In recent work, Na co-doping have found to improve the light output of Eu doped LiCaAlF<inf>6</inf> (Eu:LiCAF) for thermal neutron scintillator. We grew Eu 2% and alkali metal 1% co-doped LiSAF crystals by Micro-Pulling down method to understand the effect of alkali metal co-doping on scintillation properties and mechanism compared with LiCAF. In photo- and α-ray induced radio-luminescence spectra of the all grown crystals, the emissions from d-f transition of Eu²⁺ were observed. Without relation to excitation source, decay times of co-doped LiSAF were longer than Eu only doped one. The light yield of Na, K and Cs co-doped LiSAF under ²⁵²Cf neutron excitation were improved. Especially, K co-doped Eu:LiSAF reached 33200 ph/n, which outperformed Eu only doped one by approximately 20%. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201200205

Scopus

出版者・発行元：Physica Status Solidi C Current Topics in Solid State Physics  

Ce 2% doped LiYF4 [Ce:LYF] bulk single crystal was grown by Czochralski method and the structural phase, crystallinity, optical properties and scintillation properties were investigated. Grown Ce:LYF bulk single crystal included some cracks in the initial part of crystal and meanwhile there were no visible cracks in the center and end parts. Full width of half maximum of X-ray rocking curve on the plate crystal in center part of Ce:LYF bulk single crystal was 81.4 arcsec. Alpha-ray position in the pulse-height spectra under alpha-ray irradiation was almost quarter that of Li-glass(GS20). Decay times of the crystals in center and end parts were 69.9 and 58.3 ns, respectively. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201200290

Scopus

出版者・発行元：Physica Status Solidi C Current Topics in Solid State Physics  

Optical and scintillation properties of a 1.0-mol% Dy-doped yttrium aluminium garnet (YAG) grown under N<inf>2</inf> atmosphere and undoped YAG crystals were investigated. Both crystals were grown by the Czochralski process. The one of the undoped YAG crystal was grown in an Ar + H<inf>2</inf> (97:3) reducing atmosphere. Absorption peaks at 352 nm and 366 nm observed in 1.0-mol% Dy-doped YAG originated from 4f-4f transition of Dy³⁺. In addition, the crystal showed sharp emission lines at near 482 nm and 584 nm under 352 nm UV and alpha-ray excitation. The light output of Dy-doped YAG was estimated to be approximately 20,000 photons/(5.5-MeV alpha ray, ²⁴¹Am). The scintillation decay time constants for Dy-doped YAG crystal was around 400 ns and 40 ns. Undoped YAG crystals grown under Ar + H<inf>2</inf>(97:3) atmosphere showed absorption and excitation peak at 370 nm. A 400-nm emission peak was observed under 370-nm excitation. The light output of the crystal was also estimated to be 50,000 photons/(5.5-MeV alpha ray). The scintillation decay time constants of the crystal were around 370 ns and 50 ns. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201200325

Scopus

出版者・発行元：Physica Status Solidi C Current Topics in Solid State Physics  

10%-Ce doped GdScO<inf>3</inf> perovskite type single crystal was grown by the Czochralski process. The Ce concentration in the crystal was measured. No impurity phases were observed by powder X-ray diffraction analysis. We evaluated the optical and radiation properties of the grown crystal. Ce:GdScO<inf>3</inf> crystal showed photo- and radio-luminescence peaks due to Ce³⁺ of 5d-4f transition and colour centre. The photoluminescence decay time was sub-ns order. The relative light yield under 5.5 MeV alpha-ray excitation was calculated to be approximately 9% of BGO. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201200333

Scopus

出版者・発行元：Physica Status Solidi C Current Topics in Solid State Physics  

Ce-doped Gd<inf>3</inf>Al<inf>3</inf>Ga<inf>2</inf>O<inf>12</inf> (Ce:GAGG) crystal shows good scintillation performances, especially high light yield. However, its scintillation decay contains slower components. Such phenomenon is due to the delayed radiative recombination process which is caused by trapping effects in the transport stage of scintillation mechanism. Various defects including oxygen vacancy can give rise to shallow traps in the forbidden gap of the material which can cause such phenomena. To study the influence of such oxygen defects, 0.2-mol% Ce-doped GAGG single crystals were grown by Floating Zone method using growth atmosphere with different oxygen concentrations. The optical and scintillation properties of the crystals were examined. The light yield and emission wavelength of these samples did not depend on the oxygen content in the growth atmosphere. On the other hand, scintillation decays of the samples grown under the high oxygen concentrations (100 and 40% oxygen) were faster than that of the sample grown under the lower concentration (20%). Oxygen content in the growth atmosphere thus appears an important parameter in the optimization of the growth process of these materials. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201200327

Scopus

出版者・発行元：Journal of Crystal Growth  

Ce:LiSrAlF <inf>6</inf> and Eu:LiSrAlF <inf>6</inf> crystals with different dopant concentrations were grown by the micro-pulling-down method. The crystals with high dopant crystal included the secondary phase as clusters with the plate shape in BSE images. The secondary phases were identified CeF <inf>3</inf> and EuF <inf>2</inf>, respectively, by the EDS analysis and powder-XRD measurement. Eu concentration against the Sr sites in the Eu 2% doped LiSAF crystal were most uniform in the range 0.9-1.6 atm% using the EPMA. © 2012 Elsevier B.V.

DOI： 10.1016/j.jcrysgro.2012.02.001

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

Among the direct wide band-gap semiconductors, ZnO is an attractive scintillator for alpha particle monitoring. However, the undoped ZnO has a dominant slow luminescence around 500-600 nm due to lattice defects. In this study, the Mg-substituted ZnO ((Zn,Mg)O) single crystalline films with high crystallinity are investigated. Mg doping is found to improve the lattice order and suppress slow luminescent component around 500-600 nm. (Zn,Mg)O single crystalline films were grown by the Liquid Phase Epitaxy (LPE) method. Alpha-ray excited radioluminescence spectra of (Zn,Mg)O film show only one emission peak around 400 nm and decay time of a few nanoseconds. This emission is assigned to free exciton. Light yield of LPE grown (Zn,Mg)O film is evaluated of about 90% of BGO. © 2012 IEEE.

DOI： 10.1109/TNS.2012.2194743

Scopus

出版者・発行元：IEEE Transactions on Nuclear Science  

In this study, we investigated the relation between crystallinity and scintillation properties of Pr:LuAG crystals grown by Czochralski (Cz) method. The crystallinity was determined as the dislocation density using the X-ray rocking curve technique. The scintillation pulse-height spectra were collected under 662 keV <inf>137</inf> Cs γ-ray excitation to evaluate the light yield and energy resolution. It was confirmed that both the light yield and energy resolution correlates with the crystalinity; however, the other factors also have an influence. © 2012 IEEE.

DOI： 10.1109/TNS.2012.2189895

Scopus

出版者・発行元：Key Engineering Materials  

Ce and Mg co-doped LiCaAlF<inf>6</inf> (LiCAF) single crystals were grown by micro-pulling-down (μ-PD) method and the optical and scintillation properties of obtained crystals were measured. The grown crystals were crack-free and had 30-50 mm in length and 2 mm in diameter. Absorption coefficients were proportional to the Ce nominal concentrations. The radioluminescence spectra under 5.5 MeV alpha-ray irradiation showed emission peak at 290 and 310 nm due to Ce³⁺ 5d-4f transitions, and were agreement with those of Ce single-doped LiCAF. The highest light yield under 5.5 MeV alpha-ray irradiation of Ce 4% and Mg 2% co-doped LiCAF was found to be 0.6 times than that of lithium glass scintillator GS-20. Comparing the light yield of LiCAF samples with the fixed Ce nominal concentration and different Mg co-doped concentrations, the light yield increased with an increase of Mg nominal concentration. The alpha-ray excited decay times were constantly 45-50 ns. © (2012) Trans Tech Publications, Switzerland.

DOI： 10.4028/www.scientific.net/KEM.508.240

Open Access

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

Ce and Eu doped LiSrAlF<inf>6</inf> (LiSAF) single crystals for the neutron detection with different dopant concentrations were grown by the micro-pulling-down method (μ-PD). In Ce:LiSAF, intense emission peaks due to Ce³⁺ 5d4f transitions were observed at approximately 315 and 335 nm in photo- and α-ray induced radio-luminescence spectra. In case of Eu:LiSAFs, an intense emission peak at 375 nm due to Eu²⁺ 5d4f transition was observed in the radio-luminescence spectra. The pulse height spectra and decay time profiles were measured under ²⁵²Cf neutron irradiation to examine the neutron response. The Ce 3% and Eu 2% doped LiSAF showed the highest light yield of 2860 ph/n with 19 ns main decay time component and 24,000 ph/n with 1610 ns. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2011.08.048

Scopus

出版者・発行元：Proceedings of the 25th Workshop on Radiation Detectors and their Uses  

Scopus

出版者・発行元：Crystal Growth and Design  

We have grown Ce- and Na-co-doped LiCaAlF<inf>6</inf> (Ce, Na:LiCAF) single crystals with various Ce and Na concentrations by the micro-pulling-down (μ-PD) method. Physical properties such as crystallinity, transmittance, photoluminescence, scintillation, and radiation resistance were investigated to evaluate the effects of charge compensation by Na co-doping in the Ce-doped LiCaAlF<inf>6</inf> (Ce:LiCAF) crystal. Ce2%:LiCAF, Ce1%Na1%:LiCAF, Ce1.5%Na1.5%:LiCAF, and Ce2%Na2%:LiCAF crystals with no visible cracks and inclusions were prepared. The Ce1%Na1%:LiCAF crystal showed high crystallinity comparable to the crystal grown by the Czochralski method. In the transmittance and photoluminescence spectra of all crystals, an absorption peak around 270 nm and emission peaks around 285 and 310 nm originating from Ce³⁺ ions were observed, respectively. With increasing Ce and Na concentrations, the light yield systematically increased, and scintillation decay times decreased. Improvement of radiation resistance accomplished by charge compensation due to Na co-doping is clearly demonstrated. © 2011 American Chemical Society.

DOI： 10.1021/cg200226f

Scopus

出版者・発行元：Applied Physics Express  

A recent study has revealed that a Eu-doped LiCaAlF<inf>6</inf> (Eu:LiCAF) crystalline scintillator showed good scintillation response under thermal neutron exposure. We discover here that Eu and Na codoped LiCAF exhibits superior scintillation properties to Eu:LiCAF. We grew Eu 2% and Na 0.5, 1, and 2% codoped LiCAF by the micropulling down method. In radioluminescence spectra, they showed intense emission peaking at 370nm due to Eu²⁺ 5d-4f transition. In particular, the light yield of Eu 2% Na 2%-doped LiCAF reached 40000 ph/n, which was about 30% higher than that of Eu:LiCAF. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.4.106401

Scopus

出版者・発行元：IEEE Nuclear Science Symposium Conference Record  

The scintillation properties of undoped Lu<inf>3</inf>Ga<inf>5</inf>O <inf>12</inf> (LGG), Y<inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (YGG) and Gd <inf>3</inf>Ga<inf>5</inf>O<inf>12</inf> (GGG) crystals were investigated at room temperature. All crystals resulted in around 70-80% transmittances in wavelengths 300 nm-500 nm. In addition, GGG crystals showed a weak absorption peak around 280 nm possibility due to Gd³ 4f-4f absorption. These crystals had intrinsic luminescence peaks. The peaks of LGG, YGG and GGG crystals appeared among 300 to 400 nm. The light yields of LGG crystals were about 1,050 photons / 5.5 MeV- and YGG crystals were about 330 photons / 5.5 MeV-. In GGG, no noticeable peaks appeared. The scintillation decay time of LGG crystals radioluminescence spectra turned out to be of 1.71 ns under X-ray eicitation. © 2010 IEEE.

DOI： 10.1109/NSSMIC.2010.5873740

Scopus

出版者・発行元：Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment  

Pr³ 0.2, 0.75, and 3 mol% doped YAP single crystalline scintillators were grown by using the micro-pulling down (μ-PD) method. Pr³ 0.05 mol% doped YAP was also prepared by using the Czochralski method. In transmittance spectra, 4f5d absorption line appeared at 230 nm. The μ-PD grown crystals showed intense emission at 290 nm while the Czochralski grown one showed an emission peak at 245 nm in radio luminescence spectra under X-ray excitation. Among them, the Czochralski grown one exhibited the highest light yield under ¹³⁷Cs 662 keV excitation and the absolute light yield of this sample was estimated to be 20400±2000 ph/MeV. The decay time constants of these scintillators were around 10 ns due to Pr³ 5d4f transition. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2010.08.022

Scopus

出版者・発行元：Optical Materials  

The breast cancer is one of the most frequent cause of death among female cancer patients. However, when discovered at the early stage, the probability of recovery is very high. Therefore, the development of positron emission mammography (PEM) to detect the breast cancer at the early stage with high efficiency is demanding. As the diameter of the scanner part is small, a scintillator with faster response is required. As the recently developed Pr:LuAG has almost twice as short scintillation decay time than that of Ce:LSO, the Pr:LuAG scintillator was employed in our recently developed PEM system. One camera unit consisted of 20 × 64 scintillator pixels optically coupled with three H8500-03 multi anode photomultipliers. The Pr:LuAG pixel size is 2.1 × 2.1 × 15 mm³ and the BaSO<inf>4</inf> was used as a reflector. Four planar cameras are placed at both sides. Therefore, eight cameras were installed at both sides of the instrument. The spatial resolution was evaluated to be 1.1 mm using the ²²Na point source. Fluorodeoxyglucose with ¹⁸F hotspot image was also detected using the breast phantom. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2010.05.002

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出版者・発行元：Optical Materials  

Er- and Tm-doped LiCaAlF<inf>6</inf> (LiCAF) single crystals were grown by the micro-pulling-down (μ-PD) method. The crystals were transparent, 2.0 mm in diameter and 30-40 mm in length. Neither visible inclusions nor cracks were observed. Photoluminescence spectra of Er- and Tm-doped LiCAF were measured. Broad band emission due to the Tm³⁺ and Er³⁺ 5d-4f transitions dominated the spectrum at 163.5 and 165 nm respectively. These emissions had shortest wavelength among the fluoride crystal hosts ever reported at room temperature experiments. The vacuum ultraviolet (VUV) luminescent crystals are attractive as scintillators for radiation detectors, which employ photosensitive gases (such as TMAE or TEA) or photocathodes (such as CsI) sensitive mostly to VUV photons. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2010.04.032

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