Faculty Profiles - KOBAYASHI Makoto

Photoluminescence Properties of Double Perovskite Tantalates Activated with Mn4+, AE(2)LaTaO(6):Mn4+ (AE = Ca, Sr, and Ba) Reviewed International journal

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

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 121 ( 34 ) page： 18837 - 18844 2017.8

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

Tetravalent manganese is known as one of the candidate luminous centers to obtain red emission. There are still unclear factors in Mn4+-activated oxide phosphors to achieve intense emission. In this paper, we studied the photoluminescence properties of double perovskite-type tantalates AE(2)LaTaO(6) (AE = Ca, Sr, and Ba) activated with Mn4+. All AE(2)LaTaO(6):Mn exhibited Mn4+-emission in the deep red region under excitation by near ultraviolet-green light (300-570 nm) at room temperature. Co-substitution of Mg2+, Al3+, and Ti4+ compensates unbalanced charge caused by oxygen defects, resulting in the enhancement of Mn4(+-)emission. The present cosubstitution effect is different from the usual cosubstitution, such as the replacement of two Al3+ by Mn4+ and Mg2+, taking into consideration the charge balance between cations. Theoretical calculation of band structures based on density functional theory suggests the presence of two kinds of quenching schemes in AE(2)LaTaO(6):Mn, photoionization and electron transfer from valence band to t(2g) orbitals of Mn.

DOI： 10.1021/acs.jpcc.7b06280

Development of Crystal Growth Based on Aqueous Solution Processes Invited Reviewed

Makoto Kobayashi

Ceramics Japan Vol. 52 ( 7 ) page： 502-503 2017.7

Synthesis and photocatalytic properties of tetragonal tungsten bronze type oxynitrides Reviewed International journal

Katsuya Shimizu, Hideki Kato, Makoto Kobayashi, Masato Kakihana

APPLIED CATALYSIS B-ENVIRONMENTAL Vol. 206 page： 444 - 448 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Synthesis of a series of oxynitride Ba3-chi La chi Ta5O14-chi N1+x (x= 0-1.5) with a tetragonal tungsten bronze (TTB) structure was examined using moist-NH3 and 5% NH3-N-2 as nitriding atmosphere. The samples with x=0-1 were successfully obtained as phase pure TTB oxynitride whereas the x= 1.5 samples gave a mixture of TTB oxynitride, Ta3N5, and LaTaO4. Absorption of TTB oxynitrides in visible region was enhanced as increasing the content of nitrogen. TTB oxynitrides exhibited both of H-2 and O-2 evolution under visible light in the presence of methanol and silver ions, respectively, as sacrificial reagents. Nitrogen poor surface in the samples synthesized under moist-NH3 atmosphere was modified by annealing treatment using 5% NH3, resulting in improvement of photocatalytic activity for H2 evolution. Evaluation using monochromatic light revealed that the apparent quantum efficiency of Ba2LaTa5O13N2 was higher than that of Ba3Ta5O14N. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.apcatb.2017.01.057

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

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

CHEMISTRY LETTERS Vol. 46 ( 6 ) page： 795 - 797 2017.6

Authorship：Lead author 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 Ca(3)Ln(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