Papers by Author: Kenji Toda

Abstract: Ba2Gd3Li3Mo8O32:Eu3+ phosphor was prepared using a single mode microwave oven operated at a frequency of 2.45 GHz and a power of 500 W. The temperature of raw materials, mixtures of BaCO3, Gd2O3, Li2CO3, MoO3 and Eu2O3 subjected to microwave irradiation increased to about 1073 K in 120 s, followed by a sharp drop despite irradiating the raw materials continuously. By measuring the dielectric loss factor of the raw materials at 2.45 GHz, the temperature increased could be attributed to the fact that MoO3 absorbs a high proportion of microwave energy. In the case of the microwave heating method, the phosphor particles were highly non-aggregated.

Abstract: Photocatalysts for overall water splitting have great potential in solar energy applications. A variety of photocatalysts have shown activity for water splitting. In particular, oxysulfides are the great interest because of their ability to generate H2 and O2 from water under visible light. However, they are generally synthesized under H2S flow, which is an extremely harmful gas for humans. In this study, La2O2S2 was synthesized at low temperature without H2S gas, and its photocatalytic activity was confirmed by hydrogen generation experiments.

Abstract: Low-dimensional structure compounds as layered perovskite shows high photocatalytic activity in water splitting. In this study, we investigated that synthesis and characterization of photocatalytic activity of BaGeGa6O12 with a one-dimensional structure. BaGeGa6O12 with loading 0.3wt% RuO2 showed a photocatalytic activity for water splitting into H2 (70.6 μ mol / h) and O2 (28.1 μ mol / h).

Abstract: We report the synthesis and photocatalytic activity of CaZnGe2O6, which contains Ca2+ ions and one-dimensional GeO4 chains (Ge4+: d10 electronic configuration). This sample demonstrated the water splitting phenomenon by loading with RuO2 cocatalysis. Moreover, Ln-doped CaZnGe2O6 (where Ln = La, Ce, Pr, Nd, or Sm) shows a higher photocatalytic activity than CaZnGe2O6.

Abstract: We synthesized Sr0.7La0.2[ ]0.1Bi2Ta2O9 (SBTL , [ ] vacancy), and measured their photocatalytic activity for water decomposition under UV light irradiation after acid treatment. They showed the high photocatalytic activity under UV light irradiation (H2 evolution (213μmol / h) , O2 evolution (82μmol / h)).

Abstract: Photochemical splitting of water into H2 and O2 using solar energy is process of great economic and environmental interest. In this study, we investigated novel photocatalytic compound, Na16Ti10O28, for water splitting. Na16Ti10O28 was prepared by solid-state reaction at 900 oC for 1 h. Prepared sample was characterized using powder X-ray diffraction, diffuse reflectance spectrum, and scanning electron microscopy. As-prepared Na16Ti10O28 sample is easily hydrated in water. Hydrous Na16Ti10O28 showed H2 evolution without co-catalyst.

Abstract: Fine TiO2 particles were synthesized from titanate precursor, Na16Ti10O28, dissolved in aqueous HNO3 solution. Crystalline rutile TiO2 powders were prepared by reflux of dissolved powders in the aqueous HNO3 solution under 100 °C. Prepared TiO2 powders were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy and BET specific surface area analysis.

Abstract: New red phosphors Na3YSi2O7:Eu3+ was prepared by a conventional solid-state reaction. This silicate phosphor can be efficiently excited by near UV light, yielding an intense red emission. Under the excitation of near UV light, the emission intensity is higher than that of a commercial red phosphor Y2O2S:Eu3+.

Abstract: Eu3+ doped and undoped Y(P,V)O4 phosphors were prepared using multi-mode and single-mode microwave oven operated at 2.45 GHz. In the case of the microwave heating method, the phosphor particles were non-aggregated. A homogeneous distribution of Eu ion was observed in the microwave synthesis. No sintering behavior found in the microwave heating may be attributed to a quite shorter heating time. The Eu3+ doped sample synthesized by microwave heating showed intense red emission under UV excitation.

Abstract: A white long persistence phosphor was synthesized in a single-phase of Mg2SnO4 which was synthesized by a solid-state reaction. This phosphor crystallized in an inverse spinel structure and showed a broad-band emission from 350nm to 700nm. The afterglow was observed upon the excitation by 254nm. A Li-doped Mg2SnO4 sample showed a higher photoluminescence intensity and a longer lifetime than the non-doped one.