Faculty Profiles - TODA Kenji

Synthesis of down-converting red emission Ca14Zn6Al10-xMnxO35 phosphors for use in solar cells Reviewed

Mangyu Hur, Takaki Masaki, Kenji Toda, Dae Ho Yoon

JOURNAL OF CERAMIC PROCESSING RESEARCH 15 ( 3 ) 197 - 199 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：KOREAN ASSOC CRYSTAL GROWTH, INC

Ca14Zn6Al10-xMnxO35 (x = 1, 3, 5 mol%, CZAMO) phosphor materials were synthesized using the liquid phase precursor (LPP) method. Nanostructrued cellulose was impregnated with metal-hydrate solution and then calcined to vaporize the cellulose. The impregnated cellulose was fired at 800 to 1200 degrees C to give the CZAMO phosphors. The particle size and crystal structure of the phosphors were analyzed by FE-SEM and XRD. Nano-sized particles with a dominant Ca14Zn6Al10O35 structure (100 nm) were obtained by firing at 800 degrees C for 1 h. The red emission wavelength of the phosphors ranged from 650 to 750 nm, peaking at 713 nm.

Long phosphorescent Ca2SnO4 with minuscule rare earth dopant concentration Reviewed

Tadashi Ishigaki, Akiko Torisaka, Kentarou Nomizu, Puttaswamy Madhusudan, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato

Dalton Transactions 42 ( 14 ) 4781 - 4785 2013.4

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

Rare-earth doped Ca2SnO4 phosphors were synthesized using a conventional solid state reaction method. The red phosphorescence of Eu3+ was observed in this system with persistence time. In the as-prepared samples, the doped rare earth ions occupied both Ca and Sn sites in the host lattice. The longest phosphorescent persistence property can be achieved for the Ca2SnO4 phosphors with a 0.1% Eu dopant. Depending on the doped rare earth ions, afterglow emissions of various colors were observed. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3dt33079f

Research on new precursor for nanosheets phosphors Reviewed

K. Tanima, M. Watanabe, Y. Imanari, S. Kamei, K. Uematsu, T. Shigaki, K. Toda, M. Sato, T. Masaki, D. H. Yoon

Journal of Ceramic Processing Research 14 ( 1 ) s71 - s73 2013.3

Luminescent properties of Eu-activated Mg-Y-Si-O-N glass and crystalline phosphors Reviewed

S. Sato, S. Kamei, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, H. Sasaoka, M. Ooka, K. Nishimura

Journal of Ceramic Processing Research 14 ( 1 ) s77 - s79 2013.3

Synthesis of broadband emission phosphor Ca2KMg2(V1xPx)(3)O-12 for white light emitting diodes Reviewed

M. Maeda, K. Uematsu, S. Kamei, T. Ishigaki, K. Toda, M. Sato

JOURNAL OF CERAMIC PROCESSING RESEARCH 14 ( 1 ) S60 - S63 2013.3

Language：English Publishing type：Research paper (scientific journal) Publisher：KOREAN ASSOC CRYSTAL GROWTH, INC

We report the increased emission intensity of Ca2KMg2V3O12 by partially substituting the V5+ ion for the P5+ ion. The emission intensity of Ca2KMg2(V0.95P0.05)(3)O-12 was approximately 1.3 times greater than that of Ca2KMg2V3O12. The obtained phosphors were excited and emitted at 360 nm and 520 nm, respectively, and the emission obtained as a greenish white emission. The color coordinates of Ca2KMg2(V0.95P0.05)(3)O-12 were x = 0.377 and y = 0.463.

Synthesis of Zn2SiO4:Mn2+ using SiOx as an oxidation inhibitor Reviewed

T. Sakamoto, S. Kamei, K. Uematsu, T. Ishigaki, K. Toda, M. Sato

Journal of Ceramic Processing Research 14 ( 1 ) s64 - s66 2013.3

Enhancement of photoluminescence properties of SrAl2Si2O8:Eu2+ by a large amount of SiO2 addition Reviewed

B. S. Kim, Y. H. Song, D. S. Jo, T. Abe, K. Senthil, T. Masaki, K. Toda, D. H. Yoon

JOURNAL OF CERAMIC PROCESSING RESEARCH 14 ( 1 ) S12 - S14 2013.3

Synthesis and luminescence properties of rare earth doped Na3AlP3O9N oxynitridophosphate phosphor Reviewed

S. Sato, S. Kamei, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, H. Sasaoka, M. Ooka, K. Nishimura

Journal of Ceramic Processing Research 14 ( 1 ) s74 - s76 2013.3

Enhancement of the luminescence efficiency of Li2TiO3:Mn4+ red emitting phosphor for white LEDs Reviewed

K. Seki, S. Kamei, K. Uematsu, T. Ishigaki, K. Toda, M. Sato

Journal of Ceramic Processing Research 14 ( 1 ) s67 - s70 2013.3

Efficient red emission of blue-light excitable new structure type NaMgPO<inf>4</inf>:Eu<sup>2+</sup> phosphor Reviewed

Sun Woog Kim, Takuya Hasegawa, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato

ECS Solid State Letters 2 ( 12 ) R49 - R51 2013

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

A novel red-emitting olivine-type NaMgPO4:Eu2+ phosphor was synthesized for the first time by the melt synthesis technique using arc-imaging furnace. The NaMgPO4:Eu2+ phosphor can be efficiently excited by blue light irradiation and presents red emission band centered at 628 nm due to the 4f65d1 → 4f7 transition of Eu2+. The highest emission peak intensity was obtained for NaMgPO4:2.5mol%Eu2+, and the internal quantum efficiency of this phosphor at the excitation wavelength of 450 nm was 81%. Furthermore, these phosphors show an excellent thermal stability on the temperature quenching effect. © 2013 The Electrochemical Society.

DOI： 10.1149/2.004312ssl

Synthesis and Photoluminescence Studies of Eu3+ Activated Borosilicate Phosphor (Gd1-xEux)(3)BSi2O10 for White Light Emitting Diodes Reviewed

Tadashi Ishigaki, Puttaswamy Madhusudan, Michiyo Inoue, Shinnosuke Kamei, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato

ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY 2 ( 2 ) R3018 - R3020 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：ELECTROCHEMICAL SOC INC

Certain silicate materials with different crystal structures show excellent luminescence properties. Furthermore, these silicate compounds have high chemical and thermal stability and considered as an excellent phosphor host materials. In this study, we report (Gd1-xEux)(3)BSi2O10 as a novel ultraviolet (UV) excited white phosphors prepared under solid state reaction and their luminescence properties at 393 nm excitation were investigated in detail. The as prepared (Gd1-xEux)(3)BSi2O10 phosphors showed red emission with UV (around 580-630 nm) and near-UV light (around 250-410 nm). The chromaticity coordinates (0.60, 0.34) of the prepared borosilicate phosphor were very close to the NTSC standard value (0.67, 0.33) and its emission intensity was almost similar to commercial red phosphor Y2O2S:0.05Eu(3+). Further, as prepared (Gd1-xEux)(3)BSi2O10 material is considered to be an efficient red-emitting phosphor for UV based light emitting diodes (LED). (C) 2012 The Electrochemical Society.

DOI： 10.1149/2.007302jss

Hydrothermal synthesis of meso/macroporous BiVO4 hierarchical particles and their photocatalytic degradation properties under visible light irradiation Reviewed

Puttaswamy Madhusudan, Malahalli Vijaya Kumar, Tadashi Ishigaki, Kenji Toda, Kazuyoshi Uematsu, Mineo Sato

Environmental Science and Pollution Research 20 ( 9 ) 6638 - 6645 2013

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

An ordered hierarchical meso/macroporous monoclinic bismuth vanadate (BiVO4) particle was fabricated for the first time by a simple two-step melamine template hydrothermal method followed by calcination. The physiochemical parameters of as-prepared porous materials were characterized by means of X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Raman, Barrett-Emmett-Teller, and UV-vis techniques. The nitrogen adsorption-desorption measurement and pore size distribution curve suggest that meso/macropores exist in these hierarchical microarchitectures. Further, it is found that melamine plays a significant role in the formation of porous BiVO4 particles, and when a known amount of melamine was added, the surface area and pore size of such porous BiVO4 particles were increased. The photocatalytic activities of the as-prepared hierarchical BiVO4 samples were measured for the photodegradation of Congo red aqueous dye solution under visible light irradiation. Surprisingly, the porous BiVO4 particles showed outstanding photocatalytic activities than polycrystalline BiVO4 sample. The possible enhancement of such catalytic performance has also been further discussed. © 2013 Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s11356-013-1694-x

PubMed

Enhancement of photoluminescence properties of CaAl2Si2O8:Eu2+ by SiO2 addition Reviewed

B. S. Kim, Y. H. Song, D. S. Jo, T. Abe, K. Senthil, T. Masaki, K. Toda, D. H. Yoon

MATERIALS RESEARCH BULLETIN 47 ( 10 ) 3015 - 3019 2012.10

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

SiO2 added phosphors, CaAl2Si2O8:Eu2+ + xSiO(2) (x = 0, 1, 2, 3, 4, 5, 6 and 13 mol) were synthesized by a novel liquid phase precursor (LPP) method. The photoluminescence properties of phosphor added by 5 mol of SiO2 showed 110% enhancement in the emission intensity compared to the CaAl2Si2O8:Eu2+ phosphor. A broad emission and excitation wavelength was observed approximately from 400 nm to 600 nm centered at 430 nm and from 280 nm to 400 nm centered at 365 nm, respectively. Photoluminescence intensity of the phosphors increased continuously by SiO2 addition up to x = 5 mol and then it decreased with further addition of SiO2. The observed photoluminescence properties of the phosphors were discussed related to their crystalline structure and morphology. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.materresbull.2012.04.109

Redetermination of the low-temperature polymorph of Li 2MnSiO4 from single-crystal X-ray data Reviewed

Mineo Sato, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Hirokazu Okawa

Acta Crystallographica Section E: Structure Reports Online 68 ( 9 ) i68 - i69 2012.9

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

Crystals of dilithium manganese(II) silicate were grown under high-temperature hydro-thermal conditions in the system LiOH - MnO2 - SiO2. The title compound crystallizes in the ΒII-Li 3PO4 structure type. The coordination polyhedra of all cations are slightly distorted tetra-hedra (m symmetry for MnO4 and SiO4), which are linked by corner-sharing to each other. The vertices of the tetra-hedra point to the same direction perpendicular to the distorted hexa-gonal close-packed (hcp) array of O atoms within which half of the tetra-hedral voids are occupied by cations. In comparison with the previous refinement from powder X-ray data [Dominko et al. (2006). Electrochem. Commun. 8, 217-222], the present reinvestigation from single-crystal X-ray data allows a more precise determination of the distribution of the Li+ and Mn2+ cations, giving a perfectly site-ordered structure model for both Li+ and Mn2+.

DOI： 10.1107/S1600536812035040

Photoluminescence properties of Ba3Si6O12N2:Eu2+ oxynitride phosphor synthesized by liquid phase precursor method Reviewed

Y. H. Song, M. O. Kim, M. K. Jung, K. Senthil, T. Masaki, K. Toda, D. H. Yoon

MATERIALS LETTERS 77 121 - 124 2012.6

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

Ba3Si6O12N2 green-emitting phosphors were synthesized using oxide precursor by liquid phase precursor (LPP) method under a flowing NH3 gas. X-ray diffraction patterns showed that the prepared phosphor indicated a Ba3Si6O12N2 pure single phase. The emission spectra of synthesized phosphors under excited from UV to blue light showed a typically broad green emission wavelength which is assigned to 4f(6)5d -> 4f(7) electronic transition of Eu2+ ion. Compared with emission intensity of prepared sample, the emission intensity of Ba3- Si6O12N2 green-emitting phosphors using LPP method is more than 2.5 times than that of Ba3Si6O12N2 green-emitting one by a solid state reaction method. The synthesis of phosphor using the LPP method is expected as alternative synthesis method. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matlet.2012.02.131

Synthesis of high efficient Ca2SiO4:Eu2+ green emitting phosphor by a liquid phase precursor method Reviewed

Y. Y. Luo, D. S. Jo, K. Senthil, S. Tezuka, M. Kakihana, K. Toda, T. Masaki, D. H. Yoon

JOURNAL OF SOLID STATE CHEMISTRY 189 68 - 74 2012.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE

Green emitting Eu2+-doped Ca2SiO4 phosphors were synthesized by three different methods (a conventional solid state reaction (SSR) method, a novel liquid phase precursor approach using SiO2 sol (LPP-SiO2(sol)) and water-soluble silicon compound (LPP-WSS)). The obtained phosphors exhibited a broad excitation spectrum ranging from 225 to 450 nm and a strong green emission peak at 502 nm due to the 4f(6)5d(1)-> 4f(7)(S-8(7/2)) transition of Eu2+. The highest luminescent intensity was obtained for the samples fired at 1100 degrees C. The dependence of luminescence properties on Eu2+ concentration for the phosphors synthesized using LPP-WSS method was also examined from 0.1 to 5.0 mol% and the maximum emission intensity was observed at 3.0 mol% Eu2+. A detailed analysis using various characterizations revealed that phosphors produced by the LPP-WSS process exhibited more homogenous phase distribution and higher luminescence intensity than those from the other two processes, which suggested the potential application of Ca2SiO4:Eu2+ in white light-emitting diodes and fluorescence lamps. (C) 2011 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2011.11.046

Synthesis and photoluminescence properties of new NaAlSiO4:Eu2+ phosphors for near-UV white LED applications Reviewed

Deok Su Jo, YuanYuan Luo, Karuppanan Senthil, Kenji Toda, Bong Sung Kim, Takaki Masaki, Dae Ho Yoon

OPTICAL MATERIALS 34 ( 4 ) 696 - 699 2012.2

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

A new NaAlSiO4:0.1Eu(2+) phosphors were synthesized at different temperatures using a liquid phase precursor (LPP) technique. The XRD patterns indicate the presence of hexagonal nepheline phase for all the samples. The synthesized phosphors can be excited efficiently in the broad near-UV region. The PL emission spectra showed a broad emission peak at around 551 nm corresponding to 5d -> 41 transition of Eu2+ ions. The synthesized phosphors showed better thermal stability when compared with the standard YAG:Ce3+ phosphor. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.optmat.2011.10.004

New processing of LED phosphors Reviewed

Kenji Toda

Transactions on Electrical and Electronic Materials 13 ( 5 ) 225 - 228 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：Korean Institute of Electrical and Electronic Material Engineers

In order to synthesize LED phosphor materials, we have applied three novel synthesis techniques, "melt synthesis", "fluidized bed synthesis" and "vapor-solid hybrid synthesis", in contrast with the conventional solid state reaction technique. These synthesis techniques are also a general and powerful tool for rapid screening and improvements of new phosphor materials. © 2012 KIEEME.

DOI： 10.4313/TEEM.2012.13.5.225

Synthesis and Photoluminescence Properties of Green-Emitting Ba3Si6O12N2 Oxynitride Phosphor Using Boron-Coated Eu2O3 for White LED Applications Reviewed

Y. H. Song, B. S. Kim, M. K. Jung, K. Senthil, T. Masaki, K. Toda, D. H. Yoon

JOURNAL OF THE ELECTROCHEMICAL SOCIETY 159 ( 5 ) J148 - J152 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：ELECTROCHEMICAL SOC INC

Highly efficient Ba3Si6O12N2 green-emitting phosphors using boron-coated Eu2O3 were synthesized by a gas reduction nitridation method under flowing NH3 gas. X-ray diffraction patterns showed that the synthesized phosphor was a pure phase of Ba3Si6O12N2. The Ba3Si6O12N2 green-emitting phosphors synthesized by modification of an alumina boat were crystallized much better as well as showed higher emission intensity. The emission spectra showed a typically broad green emission band attributed to the 4f(6)5d-->4f(7) electronic transition of Eu2+ ions under excitation at 405 nm. The green-emitting Ba3Si6O12N2 phosphors that were synthesized using boron-coated Eu2O3 by modification of an alumina boat could be applied to generate white light emitting diodes. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.047205jes] All rights reserved.

DOI： 10.1149/2.047205jes