Faculty Profiles - KOBAYASHI Makoto

Papers - KOBAYASHI Makoto

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Synthesis, Structure, and Photoluminescence of a Novel Oxynitride BaYSi₂O₅N Activated by Eu²⁺ and Ce³⁺ Reviewed International journal

Makoto Kobayashi, Takuya Yasunaga, Hironori Sato, Hideki Kato, Kotaro Fujii, Masatomo Yashima, Masato Kakihana

Chemistry Letters Vol. 46 ( 6 ) page： 795 - 797 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

A novel oxynitride, BaYSi2O5N, has been synthesized by a solid-state reaction method. Its crystal structure was determined by single-crystal X-ray analysis. Eu2+- and Ce3+-doped BaYSi2O5N exhibit broad blue emission with peaks around 459 and 412 nm under excitation at 250-450 and 250-370 nm, respectively. This is the first report on the synthesis of oxynitrides in the BaO-Y2O3-SiO2-Si3N4 system.

DOI： 10.1246/cl.170144

Site occupancy and luminescence properties of Ca₃Ln(AlO)₃(BO₃)₄:Ce³⁺,Tb³⁺,Mn²⁺ (Ln = Y, Gd) Reviewed International journal

Dawei Wen, Hideki Kato, Makoto Kobayashi, Shunsuke Yamamoto, Masaya Mitsuishi, Masato Kakihana

Journal of Materials Chemistry C Vol. 5 ( 18 ) page： 4578 - 4583 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

In this work, novel single-phase white emitting Ca(3)Ln(AlO)(3)(BO3)(4): Ce3+, Tb3+, Mn2+ (Ln = Y and Gd) phosphors were synthesized by a conventional solid-state reaction method. The crystal structure and photoluminescence properties were investigated for the first time. The structure of Ca(3)Ln(AlO) (3)(BO3)(4) was formed by AlO6 octahedral chains interconnected by BO3 triangles. Along the [001] direction, the Ca/Ln cations fill in the trigonal and hexagonal tunnels. For Ca(3)Ln(AlO)(3)(BO3)(4): Ce3+ and Ca(3)Ln(AlO)(3)(BO3)(4): Mn2+, large Ce3+ preferred to occupy the smaller coordination site, while small Mn2+ occupied the larger coordination site, which was explained by the space hindrance. Due to the cation disorder, the local environment of Ce3+ was complicated and the emission band was extremely broad. In Ca(3)Ln(AlO) (3)(BO3)(4), the emission color can be tuned from blue to green or red by tuning the Ce3+-Tb3+ or Ce3+-Mn2+ concentration based on energy transfer. Thus, the combination of blue, green and red emitting Ce3+, Tb3+ and Mn2+ generated white emission.

DOI： 10.1039/c7tc00941k

Investigation of the Up-conversion Properties of Er-Yb-doped Calcium Tantalates with Various Ca/Ta Ratios Reviewed International journal

Sayaka Tamura, Michio Iwaoka, Yasushi Sato, Makoto Kobayashi, Masato Kakihana, Koji Tomita

Journal of Photopolymer Science and Technology Vol. 30 ( 4 ) page： 507 - 512 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：TECHNICAL ASSOC PHOTOPOLYMERS,JAPAN

Er3+/Yb3+ co-doped calcium tantalate up-conversion (UC) phosphors were synthesized via a parallel synthesis scheme using the gelable citrate complex method. Samples with various Ca/Ta atomic ratios were prepared, and their UC emission properties were compared. Under 980-nm near-infrared laser excitation, alpha-CazTa(2)O(7) : Er3+, Yb3+ showed an extremely weak UC emission intensity and CaTa4O11 : Er3+, Yb3+ demonstrated an excellent UC emission intensity. In addition, the local symmetry around the rare-earth dopant ions affected the UC luminescence properties.

DOI： 10.2494/photopolymer.30.507

Exploration of New Oxynitride Phosphors Using a Vacuum-Pressure Sintering Furnace Invited

Hideki Kato, Hironori Sato, Takuya Yasunaga, Makoto Kobayashi, Masato Kakihana, Fumiyoshi Isobe

Shimadzu Review Vol. 73 ( 3・4 ) page： 129-135 2016.12

Synthesis and Development of Titania with Controlled Structures Invited Reviewed

Makoto Kobayashi

Journal of the Ceramic Society of Japan Vol. 124 ( 9 ) page： 863-869 2016.9

Screening of Er³⁺/Yb³⁺ Co-doped RE-Ta-O and RE-Nb-O (RE = Y, La, or Gd) Up-conversion Phosphors Reviewed International journal

Sayaka Tamura, Michio Iwaoka, Yasushi Sato, Makoto Kobayashi, Masato Kakihana, Koji Tomita

Chemistry Letters Vol. 45 ( 8 ) page： 890 - 891 2016.8

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Upconversion (UC) phosphors comprising Er3+/Yb3+ co-doped rare-earth complex oxides, RExTayOz and RExNbyOz (RE = Y, La, or Gd), were synthesized via the gelable citrate complex method, and their UC emission properties were compared. This led to the discovery of an intense green-emitting UC phosphor, YTa7O19:Er3+/Yb3+, which is the first example of a YTa7O19 UC phosphor host material. Green UC emission obtained using optimum Er3+ and Yb3+ content was 20 times stronger than that obtained using a Y2O3 host.

DOI： 10.1246/cl.160413

Anomalous Orange Light Emitting (Sr,Ba)₂SiO₄:Eu²⁺ Phosphors for Warm White LEDs Reviewed International journal

Dawei Wen, Hiroki Kuwahara, Hideki Kato, Makoto Kobayashi, Yasushi Sato, Takaki Masaki, Masato Kakihana

ACS Applied Materials & Interfaces Vol. 8 ( 18 ) page： 11615 - 20 2016.5

Language：English Publishing type：Research paper (scientific journal)

Phosphors with sufficient red emission component are necessary for warm white light-emitting diodes. In this work on (Sr,Ba)2(1-x)Eu2xSiO4 phosphors, (Sr,Ba)1.5Eu0.5SiO4 achieved 75% of an internal quantum efficiency under excitation by blue light. Surprisingly, the (Sr,Ba)1.5Eu0.5SiO4 exhibited orange emission, against the well-known traditional green-yellow emission of (Sr,Ba)2SiO4:Eu(2+). Moreover, the concentration quenching of Eu(2+) in (Sr,Ba)2SiO4 was abnormally unobvious. With the help of calculations based on the density functional theory, it was discovered that the distinct local environment of luminescence centers rather than usual explanation such as self-absorption or intensified crystal field splitting, is responsible to the interesting red shifts in excitation and emission spectra. The refinement analysis based on X-ray diffraction revealed that the unequal distribution of Eu(2+) to two crystallographic sites caused low concentration of Eu(2+) at the 9-coordination site, inhibiting the concentration quenching. The (Sr,Ba)1.5Eu0.5SiO4 phosphor has warmer emission than the commercial Y3Al5O12:Ce(3+). This study also promotes research on the effect of site occupancy and the local environment of luminescence centers.

DOI： 10.1021/acsami.6b02237

Anisotropy in Conformation and Dynamics of a Glycolate Ion Near the Surface of a TiO₂ Rutile Crystal Between Its {001} and {110} Planes: A Molecular Dynamics Study Reviewed International journal

H. Nada, M. Kobayashi, M. Kakihana

Journal of Physical Chemistry C Vol. 120 ( 12 ) page： 6502 - 6514 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

A molecular dynamics simulation was conducted to elucidate the conformation and dynamics of a glycolate ion (CH2(OH)COO-) at the surface of a TiO2 rutile crystal. The simulation was performed for the {001} and {110} planes of the crystal. The results indicate that, for both planes, the conformation and dynamics of the ion are strongly dominated by a layered structure of water on the surface. The simulation suggests that the ion binds to the surface more stably on the {110} plane than on the {001} plane, and that the stable conformation of the ion at the surface differs between the planes: on the {110} plane the carboxyl group of the ion is preferentially oriented toward the surface, whereas on the {001} plane it is oriented toward liquid water. These simulation results are compared with the growth shapes of rutile crystals synthesized in the presence of glycolic acid, and the role of glycolate ions in controlling the morphology of rutile crystals is discussed.

DOI： 10.1021/acs.jpcc.5b11087

Effect of Site Occupancy on Deep-red Emission from Eu²⁺-activated Ca₂SiO₄ Phosphor Reviewed International journal

Hiroki Kuwahara, Yasushi Sato, Hideki Kato, Makoto Kobayashi, Takaki Masaki, Masato Kakihana

Chemistry Letters Vol. 45 ( 3 ) page： 321 - 323 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Calcium silicate cosubstituted with Sr2+ and Eu2+ was studied in order to examine the relationship between emission characteristics and Eu2+ occupancy at two types of Ca sites (Ca(1n) and Ca(2n)). The results clearly indicate that red emission of the Ca2SiO4:Eu2+ phosphor is caused by Eu2+ substitution at the Ca(2n) site. In addition, red shift in emission of Eu(2n) occurs when large amounts of Eu were substituted.

DOI： 10.1246/cl.151145

Self-assembly of polyethyleneamine-intercalated H₂Ti₂O₅ nanoparticles into spherical agglomerates Reviewed International journal

Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of Materials Research Vol. 31 ( 5 ) page： 564 - 572 2016.3

Language：English Publishing type：Research paper (scientific journal) Publisher：CAMBRIDGE UNIV PRESS

Although there are numerous reports on the synthesis of spherical materials, the development of new approaches remains important for theory construction to realize tailor-made synthesis of spherical materials. Herein, we report the synthesis of polydispersed spherical particles of H2Ti2O5 intercalated with a polyethyleneamine, such as an ethylenediamine, on the basis of a solvothermal treatment using concentrated polyethyleneamine aqueous solutions. The diameter of the micrometer-sized spheres enlarged with increasing amine concentration in the reaction solution. It was speculated that high ionic strength caused the self-assembly of polyethyleneamine-intercalated H2Ti2O5, resulting in the formation of spherical agglomerates. The spheres had a specific a surface area of 200 m(2) g(-1) and approximately 5 nm pores, and these values were controlled by amine concentration and treatment time. Conversion to single phase anatase and rutile without changes in spherical morphology was achieved by heat treatment. The present approach may assist with the design morphology of agglomerates.

DOI： 10.1557/jmr.2016.67

Hydrothermal Synthesis of Barium Tantalate Nanosheet Photocatalyst and Its Water Splitting Activity Reviewed

Soichi Takasugi, Koji Tomita, Michio Iwaoka, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of the Society of Inorganic Materials, Japan Vol. 23 ( 380 ) page： 25-29 2016

Crystal Growth of Titania Polymorphs by Hydrothermal Method(<Special Issue>Topics of Crystal Growth Related to Water) Invited Reviewed International journal

Kobayashi Makoto, Kato Hideki, Kakihana Masato

Journal of the Japanese Association for Crystal Growth Vol. 42 ( 4 ) page： 283-289 2016

Language：Japanese Publishing type：Research paper (scientific journal)

Control of crystal growth is rather important in the field of materials, because the shape directly affects their functional abilities. Our research group engages in hydrothermal synthesis of titanium dioxide, which is regarded as one of the representative ceramics, using water-soluble titanium complexes. The high chemical stability and peculiar molecule structures of these titanium complexes allowed us to use various compounds which play a role in control of crystal growth, resulting in the selective synthesis of four titanium dioxide polymorphs, that is, rutile, anatase, brookite and TiO_2(B), with a controlled shape. This paper summarizes our past study and reported researches on synthesis of titania polymorph crystals by classification of zero-, one-, two-, and three-dimensional structures.

DOI： 10.19009/jjacg.42.4_283

Hydrothermal Synthesis of Barium Tantalate Nanosheet Photocatalyst and Its Water Splitting Activity Reviewed International journal

Soichi Takasugi, Koji Tomita, Michio Iwaoka, Makoto Kobayashi, Hideki Kato, Masato Kakihana

Journal of the Society of Inorganic Materials, Japan Vol. 23 ( 380 ) page： 25-29 2016

Graphene/M_xWO₃ (M = Na, K) nanohybrids with excellent electrical properties Reviewed International journal

Bin Liu, Shu Yin, Xiaoyong Wu, Yuhua Wang, Yunfang Huang, Jihuai Wu, Tohru Sekino, Junichi Matsushita, Soo Wohn Lee, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

CARBON Vol. 94 page： 309 - 316 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Graphene/MxWO3 (M = Na, K) nanocomposites with different weight ratios were successfully synthesized using MBH4 as a reducing agent in aqueous solution, followed by crystallization of amorphous precursors under calcination in H-2 (5 vol.%)/N-2 atmosphere at 600 degrees C. The coupled samples showed good shielding properties in NIR wavelength range together with certain visible lights transparency. The as-prepared tungsten bronze nanoparticles are homogeneously anchored on graphene sheets, and the graphene/tungsten bronze nanocomposite showed an enhanced electrical conductivity with good shielding properties in the NIR range together with certain visible lights transparency. With the increment of graphene amount in the composites, the contact between the graphene sheets was enhanced, and the MxWO3 might enhance the charge transport properties of graphene by generating the short conductive path for electrons over the remained oxygenated functional groups. The synergistic effects could be observed in the composites. When 5 wt.% or more graphene were composed into MxWO3, the hybrid composite showed the higher electrical conductivity than those of uncoupled graphene and tungsten bronze alone. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2015.06.072

Large Redshifts in Emission and Excitation from Eu²⁺-Activated Sr₂SiO₄ and Ba₂SiO₄ Phosphors Induced by Controlling Eu²⁺ Occupancy on the Basis on Crystal-Site-Engineering Reviewed International journal

Yasushi Sato, Hiroki Kuwahara, Hideki Kato, Makoto Kobayashi, Takaki Masaki, Masato Kakihana

Optics and Photonics Journal Vol. 5 ( 11 ) page： 326-333 2015.11

Photoluminescence Properties of Mn⁴+</sup>-activated Perovskite-type Titanates, La₂MTiO₆:Mn⁴⁺ (M = Mg and Zn) Reviewed International journal

Yohei Takeda, Hideki Kato, Makoto Kobayashi, Hisayoshi Kobayashi, Masato Kakihana

Chemistry Letters Vol. 44 ( 11 ) page： 1541 - 1543 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

It has been found that Mn4+-activated La2MTiO6 (M = Mg and Zn) functions as novel Eu-free phosphors for red emission in this work. La2MTiO6:Mn4+ exhibited emission with a peak at 710 nm under excitation by ultraviolet to blue light (300 550 nm). La2MgTiO6:Mn4+ exhibited stronger emission than La2ZnTiO6:Mn4+. The internal quantum yield of La2MgTiO6: Mn4+ was 58.7% under the excitation at 330 nm.

DOI： 10.1246/cl.150748

A Facile One-Step Solvothermal Synthesis and Electrical Properties of Reduced Graphene Oxide/Rod-Shaped Potassium Tungsten Bronze Nanocomposite. Reviewed International journal

Bin Liu, Shu Yin, Yuhua Wang, Chongshen Guo, Xiaoyong Wu, Qiang Dong, Makoto Kobayashi, Masato Kakihana, Tsugio Sato

Journal of nanoscience and nanotechnology Vol. 15 ( 9 ) page： 7305 - 10 2015.9

Language：English Publishing type：Research paper (scientific journal)

Reduced graphene oxide (rGO)/rod-shaped potassium tungsten bronze nanocomposites with the different ratio were successfully synthesized by solvothermal reaction and followed by the reduction in H2(5 vol.%)/N2 atmosphere at 550 degrees C. The coupled samples showed excellent shielding ability of NIR light as well as certain visible lights transparency. The synergistic effects could be observed in the composites, i.e., when 15 wt% and 20 wt% of rGO which was fabricated by chemical reduction of graphene oxide, were composed into K(x)WO3, the composite showed the higher electrical conductivity than those of rGO and potassium tungsten bronze.

DOI： 10.1166/jnn.2015.10579

Synthesis of picolinate-iron(III) compounds through an aqueous solution process Reviewed International journal

Junki Sato, Makoto Kobayashi, Hideki Kato, Eunsang Kwon, Masato Kakihana

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 123 ( 1441 ) page： 751 - 755 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

A novel picolinate-iron(III) compound, Fe(C6H4NO2)(2)(OH) (1), was synthesized from an aqueous solution of a picolinate-iron(II) complex. Compound 1 was obtained by a thermal treatment of the picolinate-iron complex aqueous solution, whose pH was adjusted to 3-7, containing more than twice molar picolinic acid (Hpa) to Fe at 353K for 72 h. When the iron aqueous solution in the presence of more than six times molar Hpa to Fe at pH 2-5 was heated, Fe(C6H4NO2)(3)center dot H2O (2) appeared. Millimeter-sized yellow-green single crystals of 2 could be obtained by the heat treatment of the picolinate-iron aqueous solution, whose pH was adjusted to 3, with Fe2+:Hpa = 1: 10 at 373K for 72 h. Formation mechanism of 1 and 2 was also discussed through investigations of relationship between synthesis conditions and products. Our approach opens a promising new route for preparation of precursors for synthesis of high functional ceramics and development of new organic-inorganic hybrids. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.751

Novel Titanium Complexes with a Reversible Structural Change on Solvent Adsorption and Desorption Reviewed International journal

Makoto Kobayashi, Tatsuya Okuhara, Hideki Kato, Sota Sato, Masato Kakihana

Chemistry Letters Vol. 44 ( 8 ) page： 1050 - 1052 2015.8

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Two novel pyrazine-2-carboxylate titanium complexes were synthesized from an aqueous solution (1) and 1 in N,N-dimethylformamide (DMF) (2). The structure of 2 was determined to be [Ti6O8(C4H3N2COO)(8)(C3H7NO)(4)]center dot 4C(3)H(7)NO center dot H2O by single-crystal X-ray analysis. Both complexes exhibited solvent adsorption desorption accompanying reversible structural change. 1 and 2 were compatible, and 1 was vital for the synthesis of 2. The degassed 1 showed gate adsorption property for water vapor.

DOI： 10.1246/cl.150393

Discovery of Novel Delafossite-type Compounds Composed of Copper(I) Lithium Titanium with Photocatalytic Activity for H₂ Evolution under Visible Light Reviewed International journal

Hideki Kato, Tsuyoshi Fujisawa, Makoto Kobayashi, Masato Kakihana

CHEMISTRY LETTERS Vol. 44 ( 7 ) page： 973 - 975 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：CHEMICAL SOC JAPAN

Novel delafossite-type compounds Cu(Li1/3Ti2/3)O-2 with 3R- and 2H-type structures have been discovered through the reaction between Li4Ti5O12 and Cu2O. Cu(Li1/3Ti2/3)O-2 is the first Cu(I)-titanate containing no d(n) (n = 1-9) metal ions. It has been found that Cu(Li1/3Ti2/3)O-2 with a band gap of 2.1 eV functions as a photocatalyst for H-2 evolution under visible light irradiation.

DOI： 10.1246/cl.150341

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