Faculty Profiles - TODA Kenji

Luminescence enhancement of LiSrPO4:Eu2+ phosphor by Mg2+ ion addition Reviewed

Kamei Shinnosuke, Tomoki Hatsumori, Takuya Hasegawa, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato

Materials Research Innovations 2018.6

Synthesis of High-Efficiency Red-Emission Ca14Zn6Al9.97Mn0.03O35 Phosphors with Particle Control Reviewed

Man Gyu Hur, Seung Hee Choi, Seok Bin Kwon, Takaki Masaki, Kenji Toda, Dae Ho Yoon

Ceramics International 44 15868 - 15872 2018.6

Synthesis of Na<inf>2</inf>FePO<inf>4</inf>F using polytetrafluoroethylene Reviewed

Atsushi Tsu-Ura, Hirotaka Torii, Takuya Hasegawa, Dai Murayama, Sun Woog Kim, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato

Journal of the Ceramic Society of Japan 126 ( 5 ) 336 - 340 2018.5

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

© 2018 The Ceramic Society of Japan. All rights reserved. Polytetrafluoroethylene (PTFE), composed of fluorine and carbon atoms, has a potential to produce carbon-coated fluorides in the calcination of inorganic compounds. We synthesized high voltage cathode material for Na ion secondary battery, Na2FePO4F, using PTFE as the carbon-coating and fluorine source. The Na2FePO4F carbon-coated by a thermal decomposition of PTFE showed high discharge capacity (64.4 mAh g11) at the first cycle of galvanostatic cycling by the improvement of conductivity.

DOI： 10.2109/jcersj2.17230

Paradigm Change for Solid State Reactions: Synthesis of Lithium Orthophosphate Li3PO4 Nanoparticles by a Water Assisted Solid State Reaction (WASSR) Method Reviewed

Sun Woog Kim, Kenji Toda, Takuya Hasegawa, Mizuki Watanabe, Tatsuro Kaneko, Ayano Toda, Atsushi Itadani, Mineo Sato, Kazuyoshi Uematsu, Tadashi Ishigaki, Junko Koide, Masako Toda, Yoshiaki Kudo, Takaki Masaki, Dae Ho Yoon

Science of Advanced Materials 10 ( 4 ) 592 - 596 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER SCIENTIFIC PUBLISHERS

Lithium orthophosphate Li3PO4 nanoparticles were synthesized through a water assisted solid state reaction (WASSR) method. The nanoparticles obtained in this study adopt a stable orthorhombic structure (beta-type), which is a low temperature phase, in a single phase with high crystallinity. The Li3PO4 nanoparticles have a granular particle morphology and the particle size is less than 50 nm.

DOI： 10.1166/sam.2018.2844

Structure of triaquatris(1,1,1-trifluoro-4-oxo-pentan-2-olato)cerium(III) as a possible fluorescent compound Reviewed

Atsuya Koizumi, Takuya Hasegawa, Atsushi Itadani, Kenji Toda, Taoyun Zhu, Mineo Sato

Acta Crystallographica Section E: Crystallographic Communications 74 229 - 232 2018.2

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

© 2018 International Union of Crystallography. Luminescence due to the d-f transition of Ce3+ is quite rare in metal-organic complexes where concentrate quenching frequently occurs. One of the possible ways to avoid this is to design an architecture with elongated metal-metal distances. In the structure of the title complex, triaquatris(1,1,1-trifluoro-4-oxopentan-2-olato-2O,O0)cerium(III), [Ce(C5H4F3O2)3(H2O)3], the CeIII complex is linked to neighbouring ones by hydrogen bonding. Within the complex, the CeIII atom is coordinated by nine O atoms from three 1,1,1-trifluoro-4-oxopentan-2-olate (tfa) anions as bidentate ligands and three water molecules as monodentate ligands. Thus, the coordination number of CeIII atom is nine in a monocapped square-antiprismatic polyhedron. The F atoms of all three independent CF3 groups in tfa are disordered over two positions with occupancy ratios of about 0.8:0.2. The intermolecular hydrogen bonds between the ligands involve tfa-water interactions along the [110] and [110] directions, generating an overall two-dimensional layered network structure. The presence of the F atoms in the tfa anion is responsible for an increased intermolecular metal-metal distance compared to that in the analogous acetylacetonate (acac) derivatives. Fluorescence from Ce3+ is, however, not observed.

DOI： 10.1107/S2056989018001135

Synthesis of nano-sized materials using novel water assisted solid state reaction method Reviewed

Kenji Toda, Tatsuro Kaneko, Takuya Hasegawa, Mizuki Watanabe, Yusuke Abe, Takeshi Kuroi, Mineo Sato, Kazuyoshi Uematsu, Sun Woog Kim, Yoshiaki Kudo, Takaki Masaki, Dae Ho Yoon

Key Engineering Materials 777 KEM 163 - 167 2018

Language：English Publishing type：Research paper (international conference proceedings)

© 2018 Trans Tech Publications, Switzerland. We report synthesis of nano-sized oxide materials using a novel water assisted solid state reaction (WASSR) method. This novel soft chemical synthesis method is very simple and can synthesize nanoparticle materials just by storing or mixing raw materials added a small amount (typically 10wt%) of water in a reactor at low temperature below 373 K. Combinations of raw materials have a significant influence on the reaction rate.

DOI： 10.4028/www.scientific.net/KEM.777.163

Luminescence property of silicate phosphor, Ba9Sc2Si6O24:Ce, synthesized by melt quenching technique Reviewed

Kenji Toda, Atsushi Tsu-Ura, Minenori Katsu, Shin-Nosuke Kamei, Tadashi Ishigaki, Kazuyoshi Uematsu, Mineo Sato

Key Engineering Materials 766 186 - 190 2018

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Trans Tech Publications Ltd

Well-grown Ba9Sc2Si6O24:Ce3+ phosphors were synthesized by a novel melt quenching synthesis method. Sintered phosphor balls with excellent luminescent characteristics were obtained. This method is useful tool for rapid screening of phosphor materials.

DOI： 10.4028/www.scientific.net/KEM.766.186

Bluish-White Luminescence in Rare-Earth-Free Vanadate Garnet Phosphors: Structural Characterization of LiCa3MV3O12 (M = Zn and Mg) Reviewed

Takuya Hasegawa, Yusuke Abe, Atsuya Koizumi, Tadaharu Ueda, Kenji Toda, Mineo Sato

Inorganic Chemistry 57 ( 2 ) 857 - 866 2017.12

Nanophosphors synthesized by the water assisted solid state reaction (WASSR) method: Luminescence properties and reaction mechanism of the WASSR method Reviewed

Sun Woog Kim, Takuya Hasegawa, Mizuki Watanabe, Masaru Muto, Toshiya Terashima, Yusuke Abe, Tatsuro Kaneko, Ayano Toda, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato, Emiko Kawakami, Junko Koide, Masako Toda, Yoshiaki Kudo, Takaki Masaki, Dae Ho Yoon

Applied Spectroscopy Reviews 52 ( 10 ) 1 - 18 2017.10

Yellow MgV2O6 center dot 2H(2)O nanophosphor synthesized by a water-assisted solid-state reaction (WASSR) method at low temperature below 80 degrees C Reviewed

Sun Woog Kim, Yusuke Abe, Mizuki Watanabe, Takuya Hasegawa, Masaru Muto, Ayano Toda, Tadashi Ishigaki, Kazuyoshi Uematsu, Kenji Toda, Mineo Sato, Emiko Kawakami, Junko Koide, Masako Toda, Yoshiaki Kudo, Toshiyuki Masui, Takaki Masaki, Dae Ho Yoon

DYES AND PIGMENTS 145 339 - 344 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Magnesium metavanadate dihydrate (MgV2O6.2H(2)O) was synthesized as a nanophosphor by a water assisted solid-state reaction (WASSR) method, and its crystal structure and luminescence properties were investigated in detail. MgV2O6.2H(2)O has an orthorhombic structure with space group Pnma. In the crystal structure, the MgO6 octahedra and VO4 tetrahedra formed a layered structure in the direction of the b axis, and the VO4 tetrahedra formed a chain structure along the a axis. The nanophosphor showed broad and strong optical absorption in the near-ultraviolet region and exhibited a broad yellow emission peak at 563 nm. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.dyepig.2017.06.024

Synthesis and optical properties of P 5+ co-doped Ba 3 SiO 5 :Eu 2+ orange persistent phosphor Reviewed

Seung Hee Choi, Seok Bin Kwon, Usama Bin Humayoun, Won Kyu Park, Kenji Toda, Masato Kakihana, Takaki Masaki, Woo Seok Yang, Young Hyun Song, Dae Ho Yoon

Dyes and Pigments 148 460 - 464 2017.9

Stabilization of novel high temperature phase yellow-emitting σ-type (Ba<inf>1-: X - Y</inf>Eu<inf>x</inf>Mg<inf>y</inf>)<inf>2</inf>P<inf>2</inf>O<inf>7</inf> phosphors using a melt synthesis technique Reviewed

H. Nakagawa, S. W. Kim, T. Hasegawa, S. Hasegawa, T. Ishigaki, K. Uematsu, K. Toda, H. Takaba, M. Sato

Inorganic Chemistry Frontiers 4 ( 9 ) 1562 - 1567 2017.9

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

© 2017 the Partner Organisations. Novel Eu2+-activated phosphate phosphors based on high-temperature phase σ-Ba2P2O7, which is an unstable phase at room temperature, were synthesized for the first time by a melt synthesis technique using an arc-imaging furnace. By doping Mg2+ into the host lattice, Eu2+-activated σ-Ba2P2O7 phosphors were successfully obtained in a single phase form of a hexagonal structure and the emission intensity was also effectively enhanced. The relative emission peak intensity of the σ-(Ba0.67Eu0.03Mg0.30)2P2O7 phosphor was 315% of that for the σ-(Ba0.97Eu0.03)2P2O7 phosphor. The emission color tunable from green emission with a peak at 516 nm to yellow emission with a peak at 551 nm can be achieved by controlling the Mg2+ content in the σ-(Ba0.97-yEu0.03Mgy)2P2O7 phosphors.

DOI： 10.1039/c7qi00359e

Unusual, broad red emission of novel Ce3+ -activated Sr3Sc4O9 phosphors under visible-light excitation Reviewed

Takuya Hasegawa, Sun Woog Kim, Tadaharu Ueda, Tadashi Ishigaki, Kazuyoshi Uematsu, Hiromitsu Takaba, Kenji Toda, Mineo Sato

JOURNAL OF MATERIALS CHEMISTRY C 5 ( 36 ) 9472 - 9478 2017.9

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

Most conventional white light emitting diodes (white-LEDs) that are widely used as a new lighting system in next generation lights with Y3Al5O12: Ce3+ (YAG: Ce3+)-based phosphors have a low colour rendering index (CRI) because the YAG: Ce3+ phosphor shows a weak emission intensity in the red spectral region. Therefore, discovering a red-emitting phosphor with a high-efficiency is quite important to enhance the CRI of white-LEDs. In this study, we successfully discovered a novel, red-emitting Ce3+-activated Sr3Sc4O9 phosphor that can be excited by blue-light irradiation at 425 nm. A crystal structure of the host material was first determined by Rietveld refinement, which indicated that it should be isostructural with Ba(3)Ln(4)O(9) (Ln = Sc, Y and Dy-Lu). As the Ce3+ content increased, the X-ray diffraction patterns shifted to a lower angle, which suggested that the Ce3+ ion could substitute Sc in the Sr3Sc4O9 host. Under UV and blue-light excitation, the Ce3+-activated Sr3Sc4O9 phosphor exhibited a broad emission band with a maximum peak at 620 nm, and its full width half maximum (FWHM) was 180 nm (4530 cm(-1)). The highest emission intensity was obtained for Sr-3(Sc0.997Ce0.003)(4)O-9, and the internal quantum efficiency of this phosphor under excitation at 425 nm was 53%. To the best of our knowledge, the emission band of the Ce3+-activated Sr3Sc4O9 phosphor is the longest wavelength for a reported Ce3+-activated oxide phosphor.

DOI： 10.1039/c7tc03203j

Exquisite morphology, highly emissive yellow Sr1.44Ba0.46SiO4:0.1Eu(2+) phosphor synthesized by a liquid phase precursor process Reviewed

Usama Bin Humayoun, Young Hyun Song, Seok Bin Kwon, Kakihana Masato, Kenji Toda, Yasushi Sato, Takaki Masaki, Dae-Ho Yoon

DYES AND PIGMENTS 142 147 - 152 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Yellow phosphors are the major components of contemporary solid-state lights. YAG:Ce3+ is a widely adopted yellow phosphor component; however, it too has limitations. Here, we report the synthesis and application of a very highly efficient yellow-emitting orthosilicate phosphor. Yellow-emitting Sr1.44Ba0.46SiO4:0.1Eu(2+) was synthesized by an unconventional cellulose template liquid phase precursor process (CTLPP). The naturally abundant and nonhazardous cellulose template facilitates efficient synthesis at lower temperatures. The synthesized phosphor was indexed to alpha-Sr2SiO4 phase and exhibited broad excitation and broad emission with a peak at 545 nm, very high intensity, almost 130% of commercial YAG upon excitation at 450 nm. The morphology of the phosphors was also nearly spherical, which also enables their use in WLEDs. Use of non-stoichiometric Si precursors (i.e. Sr1.44Ba0.46SixO4:0.1Eu(2+), x = 0.95, 1.0 and 1.05) in the process resulted in remarkable effects on the morphology (size and surface) and luminescent characteristics and exceptional quantum efficiencies of the phosphors. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.dyepig.2017.03.029

Improvement of luminescence properties of rubidium vanadate, RbVO3, phosphors by erbium doping in the crystal lattice Reviewed

S. W. Kim, T. Hasegawa, M. Muto, A. Toda, T. Kaneko, K. Sugimoto, K. Uematsu, T. Ishigaki, K. Toda, M. Sato, J. Koide, M. Toda, Y. Kudo

NEW JOURNAL OF CHEMISTRY 41 ( 12 ) 4788 - 4792 2017.6

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

Greenish-white emitting Rb1-xErxVO3 (0 <= x <= 0.10) phosphors were synthesized by a conventional solid state reaction method. The thermal quenching effect of the RbVO3 phosphors was effectively improved by Er3+ doping into the RbVO3 lattice. Consequently, the emission peak intensity of the phosphors was successfully enhanced by Er3+ doping, and the internal quantum efficiency of Rb0.99Er0.01VO3 under excitation at 360 nm was 80%.

DOI： 10.1039/c6nj03823a

On the possibility of polystyrene-derived carbon coating for NASICON-type Na3V2(PO4)(3) composites as cathode materials for sodium-ion batteries Reviewed

Dai Okada, Takumi Fugane, Yuka Matsumoto, Takuya Hasegawa, Atsushi Itadani, Kazuyoshi Uematsu, Kenji Toda, Hideki Hashimoto, Jun Takada, Mineo Sato

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 125 ( 4 ) 322 - 325 2017.4

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

We here prepared polystyrene-derived carbon-coated Na3V2(PO4)(3) composite (NVP/C) cathode materials via a solid-phase reaction using a mixture of NVP precursor and polystyrene (as the carbon source), followed by calcination at high temperatures. Using this method, we were able to obtain active NVP materials with relatively high purity while allowing a uniform surface coating with carbon layers about 3-4 nm thick. This structure significantly prevented NVP particle growth even after calcination at high temperatures. The NVP/C material calcined at 700 degrees C exhibited the best charge-discharge performance among the samples studied. (C) 2017 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.16266

Discovery of novel inorganic Mn5+-doped sky-blue pigments based on Ca6BaP4O17: Crystal structure, optical and color properties, and color durability Reviewed

Sun Woog Kim, Go Eun Sim, Ji Young Ock, Jeong Hun Son, Takuya Hasegawa, Kenji Toda, Dong Sik Bae

DYES AND PIGMENTS 139 344 - 348 2017.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

Novel inorganic sky-blue pigments, Ca6Ba(P1-xMnx)4O(17) (0 <= x <= 0.13) were synthesized in a single phase form by a conventional solid-state reaction method and their color properties were investigated in the detail. The pigments exhibited strong optical absorption in the UV and the yellow-red light regions due to the cT transition in MnO4 tetrahedra and the DMSO-d(6) transitions of Mn5+, which is the origin of the sky-blue color. The optimization of the composition resulted in the attainment of the highest sky-blue hue for the Ca6Ba(P0.99Mn0.01)4O(17), where the L*, a*, b*, C, and H values are 75.47, -11.67, -10.29, 15:6, and 221.4 degrees, respectively. These pigments showed a low chemical stability of color for acid/alkali solution, whereas the pigments showed an excellent color durability for heat and light. Although they are required to improve the chemical stability of color, the present pigment could be an attractive candidate as a novel environment friendly inorganic sky-blue pigment.(C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.dyepig.2016.12.038