Faculty Profiles - TODA Kenji

Papers - TODA Kenji

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Origin and model for cooperative host-guest interaction affecting the orientation of guests in oriented nematic hosts Reviewed

Michio Kobayashi, Ken-ichi Kumagai, Toshihiko Hoshi, Takuya Yamaguchi, Hirobumi Sato, Kenji Toda, Yoshie Tanizaki, Tetsutaro Yoshinaga

MOLECULAR CRYSTALS AND LIQUID CRYSTALS 469 31 - 49 2007

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

It has been observed for the binary systems of oriented nematic hosts and nonmesomorphic guests (substituted anthraquinones) that the orientational orders of amino-substituted anthraquinones ascend with increasing guest concentrations. A new quantitative anti experimental procedure has been proposed for obtaining the host-guest isotropic dispersion, isotropic electrostatic, anisotropic dispersion, and anisotropic electrostatic interaction energies. Among these four host-guest interaction energies, the host-guest isotropic dispersion interaction energy alone is demonstrated to be well correlated with the concentration dependence of the orientational order of the guest. A model is also proposed for the cooperative and isotropic host-guest interaction.

DOI： 10.1080/1542140070143187

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Removal of Fluorinefrom Waste Water by Ettringite Reviewed

T. Tokumitsu, K. Toda, H. Morinaga, K. Sato, K. Uematsu, M. Sato

ITE LETTERS 7 352 - 355 2006.12

Self Assemble Synthesis of Potassium Niobate at Room Temperature Reviewed

K. Toda, A. Sugawara, K. Uematsu, M. Sato, M. Osada

Key Engineering Materials 320 7 - 10 2006.12

New silicate phosphors for a white LED Invited Reviewed

Kenji Toda, Yoshitaka Kawakami, Shin-ichiro Kousaka, Yutaka Ito, Akira Komeno, Kazuyoshi Uematsu, Mineo Sato

IEICE TRANSACTIONS ON ELECTRONICS E89C ( 10 ) 1406 - 1412 2006.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

We focus on the development of new silicate phosphors for a white LED. In the europium doped silicate system, four LED phosphor candidates-Li2SrSiO4:Eu2+, Ba9Sc2Si6O24:Eu2+, Ca3Si2O7:Eu2+ and Ba2MgSi2O7:Eu2+ were found. Luminescent properties under near UV and visible excitation were investigated for the new Eu2+ doped LED silicate phosphors. These new phosphors have a relatively strong absorption band in a long wavelength region.

DOI： 10.1093/ietele/e89-c.10.1406

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Development of an open-ended coaxial line probe for measurement of dielectric properties of inorganic materials at high temperature Reviewed

Kazuyoshi Uematsu, Jyunji Tsuchida, Mineo Sato, Kenji Toda

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 89 ( 8 ) 2638 - 2640 2006.8

Language：English Publishing type：Research paper (scientific journal) Publisher：BLACKWELL PUBLISHING

An open-ended coaxial line probe for dielectric measurements at high temperatures was developed. The probe, which was fabricated using stainless steel as the center and outer conductors and quartz wool as an insulator, can function well up to 800 degrees C. The dielectric properties of the raw materials and resultant materials were measured using a network analyzer that was equipped with the open-ended coaxial line probe at high temperatures to clarify the formation reaction process of YVO4:Eu3+ and Mg2SnO4:Mn2+ phosphors using a microwave heating method. The developed probe was confirmed to be effective for reaction-process analyses at high temperatures.

DOI： 10.1111/j.1551-2916.2006.01074.x

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Luminescence properties of long-persistence silicate phosphors Reviewed

Y Ito, A Komeno, K Uematsu, K Toda, M Sato

JOURNAL OF ALLOYS AND COMPOUNDS 408 907 - 910 2006.2

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

Tb3+-doped and (Ce3+, Tb3+)-codoped Ca0.5Sr1.5Al2SiO7 were prepared using a solid-state reaction at 1273 K for 3 h in air and 1623 K for 6 h in a weakly reductive atmosphere of 5% H-2-95% N-2 gas. The resultant (Ce3+, Tb3+)-codoped Ca0.5Sr1.5Al2SiO7 phosphor shows four main emission peaks: one at 386 run for Ce3+ and three at 483, 542 and 591 nm for Tb3+. Emission intensity of Tb3+ in the (Ce3+, Tb3+)-codoped phosphor was five times greater than that of the Tb3+ single-doped phosphor because of the energy transfer from Ce3+ to Tb3+. The codoped phosphor showed long-persistence white phosphorescence. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.132

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VUV phosphors in the SrO-B2O3-P2O5 ternary system Reviewed

Y Komatsu, A Komeno, K Toda, K Uematsu, M Sato

JOURNAL OF ALLOYS AND COMPOUNDS 408 903 - 906 2006.2

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

Photoluminescence properties under vacuum ultraviolet (VUV, 147 nm) excitation were investigated for a new borophosphate compound. The new phosphor, Sr6BP5O20, has a relatively strong absorption band in a short wavelength region because of the strong covalent characters of B-O and P-O bonds. The phosphor activated by Eu2+ showed a strong blue luminescence. The luminance is about 2.2 times as bright as a commercial blue phosphor, BaMgAl10O17:Eu2+. The phosphor is an attractive candidate of new phosphors for plasma display panels and mercury-free fluorescent lamps. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.098

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Recent research and development of VUV phosphors for a mercury-free lamp Reviewed

K Toda

JOURNAL OF ALLOYS AND COMPOUNDS 408 665 - 668 2006.2

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

This study specifically addresses development of new inorganic oxide phosphors for a Xe-discharge mercury-free lamp. We describe the relationship between the luminescence property under vacuum ultraviolet (VUV) excitation and the crystal structure of new VUV phosphors. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.080

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VUV properties of Eu-doped alkaline earth magnesium silicate Reviewed

A Komeno, K Uematsu, K Toda, M Sato

JOURNAL OF ALLOYS AND COMPOUNDS 408 871 - 874 2006.2

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

Plasma display panels (PDP) are most promising for large flat panel displays at present. However, luminescence efficiency and lifetime of PDP phosphors should be improved. Alkaline earth silicates show remarkable properties as phosphor hosts with various crystal structures and high chemical stability. Availability of Ba2MgSi2O7 has received attention as a host for vacuum ultraviolet (VUV) excitable phosphor. Blue-green phosphor Ba2MgSi2O7:Eu2+ with a high thermal quenching temperature [G. Blasse, W.L. Wanmaker, J.W. ver Vrugt, A. Bril, Philips. Res. Rep. 23 (1968) 189-200] exhibit high luminance (45% of commercial green VUV phosphor Zn2SiO4:Mn2+) under VUV excitation without optimization of synthesis condition and emission color. Ba2MgSi2O7 is promising candidate for the new VUV phosphor in PDP and mercury-free lamp application. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.070

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Characterization of YVO4 : Eu3+ phosphors synthesized by microwave heating method Reviewed

K Uematsu, A Ochiai, K Toda, M Sato

JOURNAL OF ALLOYS AND COMPOUNDS 408 860 - 863 2006.2

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

YVO4:Eu3+ phosphors were prepared using a domestic microwave oven operated at 2.45 GHz with 500 W. The temperature of raw materials with mixtures of Y2O3, V2O5 and Eu2O3 that were irradiated with the microwave increased to about 840 degrees C within 150 s. Subsequently, the temperature dropped sharply in spite of the continuing microwave irradiation. Measurement of the dielectric loss factor of the raw materials and products at 2.45 GHz at temperatures from 25 degrees C to 800 degrees C revealed a high absorption efficiency of microwave energy by V2O5, which provided a rapid increase in the raw material's temperature. A low dielectric loss factor observed for YVO4:Eu engendered a sharp temperature drop after completion of the reaction of Y2O3 with V2O5, (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.081

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Luminescent properties of red long persistence phosphors, BaMg2Si2O7 : Eu2+, Mn2+ Reviewed

S Abe, K Uematsu, K Toda, M Sato

JOURNAL OF ALLOYS AND COMPOUNDS 408 911 - 914 2006.2

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

Long persistence phosphors of BaMg2Si2O7:Eu2+, Mn2+, with red emission were prepared using a conventional solid state reaction. Phosphors doped only With Eu2+ emitted 1400 nm violet light; those doped only with Mn2+ emitted red light that was hardly visible. Phosphors doped with both Eu2+ and Mn2+ showed two emission peaks of 400 and 660 nm, exhibiting a reddish luminescence to the naked eye. These facts suggested an energy transfer from Eu2+ to Mn2+. Non-stoichiometric co-doped phosphors with a deficient Ba component showed long persistence phosphorescence with reddish color. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.03.092

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Powder neutron diffraction study of layered perovskite, KCa 2Nb3O10 Reviewed

Toshiaki Tokumitsu, Kenji Toda, Tsukuru Aoyagi, Daiki Sakuraba, Kazuyoshi Uematsu, Mineo Sato

Journal of the Ceramic Society of Japan 114 ( 1333 ) 795 - 797 2006

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramic Society of Japan

Crystal structure of a layered perovskite, KCaiNbjOm, was determined by the Rietveld refinement method for a powder neutron diffraction pattern. The compound crystallizes a monoclinic system with a space group P21/m (No. 11) and lattice parameters of a = 0.77418 (6) nm, 6 = 0.77073(6) nm, c = 1.4859(1) nm, β = 97.51(1)°.

DOI： 10.2109/jcersj.114.795

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Removal of fluoride from aqueous solution by ettringite Reviewed

Toshiaki Tokumitsu, Kenji Sato, Kenji Toda, Hiroko Morinaga, Kazuyoshi Uematsu, Mineo Sato

Journal of the Ceramic Society of Japan 114 ( 1332 ) 729 - 732 2006

Language：English Publishing type：Research paper (scientific journal) Publisher：Ceramic Society of Japan

In order to purify waste water containing fluoride, the calcium additive method has usually been used to recover fluoride ions in the form of refractory calcium fluoride. In this case, the removable fluoride concentration is limited to be 10-15 mg/1 due to the solubility of calcium fluoride. In this study, we report 3CaO·Al2O3·3CaSO4· 32H2O (ettringite) as a highly absorbent substance for the fluoride. The fluoride concentration of the water treated with the ettringite was achieved to be less than 8 mg/l without sludge.

DOI： 10.2109/jcersj.114.729

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Possibility of superconductivity in a layered perovskite niobate, KCa 2Nb3O10, synthesized by an ion exchange reaction Reviewed

Sachi Takezawa, Takashi Teranishi, Hironori Ishikawa, Toshiaki Tokumitsu, Kenji Toda, Kazuyoshi Uematsu, Mineo Sato

Journal of the Ceramic Society of Japan 114 ( 1334 ) 861 - 865 2006

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Ceramic Society of Japan

We prepared low temperature phase of triple layered perovksite KCa 2Nb3O10 by an ion-exchange reaction. Liintercalated low temperature phase, Li0.79KCa2Nb 3O10, shows strong diamagnetic signal around at 7.8 K. The magnetic phase transition temperature of Li-intercalated low temperature phase is higher than that of Li-interca-lated high temperature phase.

DOI： 10.2109/jcersj.114.861

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Synthesis of KNbO3 thin film by self-assembly of perovskite nanosheets Reviewed

A. Sugawara, K. Uematsu, K. Toda, M. Sato

Transactions of the Materials Research Society of Japan 30 583 - 586 2005.12