Papers by Author: Minoru Hanaya

Abstract: La₂Ti₂O₇:Pr powder was prepared by a solid-state reaction method. Photoluminescence due to f-f transitions of Pr³⁺ was induced by band-gap excitation of La₂Ti₂O₇. La₂Ti₂O₇:Pr thin film was prepared by sol-gel and spin-coating methods. The thin film showed visible electroluminescence due to f-f transition of Pr³⁺ by applying ac voltages.

Abstract: The effect of surface modification to dye-adsorbed TiO₂ electrodes in alkoxysilyl dye-sensitized solar cells on the photovoltaic performance was investigated with using alkylcarboxylic acids with different alkyl-chain lengths as surface modifiers. More effective suppression of a back-electron-transfer reaction was observed with the increment of the amount of the adsorbed modifier on the dye-adsorbed TiO₂ electrode and with lengthening the alkyl chain of the alkylcarboxylic acid. The photovoltaic performance of the cells was confirmed to be improved by the surface modifications of the dye-adsorbed TiO₂ electrodes using alkylcarboxylic acids, and the necessities of tuning the surface-modification degree and the selection of the alkyl-chain length with regarding the molecular size of the sensitizing dye were exhibited for the efficient improvement of the photovoltaic performance of the cell.

Abstract: The effect of the introduction of a CF₃ group to a silyl-anchor moiety of the sensitizer on the sensitizing property for the dye-sensitized solar cell was examined by using alkoxysilyl-anchor azobenzene dyes. The cell sensitized by the silyl-anchor dye with the electron-withdrawing CF₃ group in the silyl-anchor moiety exhibited higher photovoltaic performance than that by the silyl-anchor dye without the CF₃ group.

Abstract: Powder samples of (Ca,Sr)TiO₃:Er were prepared by a solid-state reaction method. Photoluminescence due to f-f transitions of Er³⁺ was not induced by band-gap excitation of (Ca,Sr)TiO₃ but by f-f transitions of Er³⁺. An electroluminescent device in which thin films of Ca_0.6Sr_0.4TiO₃:Er and SnO₂:Sb are stacked alternately was prepared by sol-gel and spin-coating methods. Very weak electroluminescence due to f-f transition of Er³⁺ was observed in the device.

Abstract: Allylsilyl and hydrosilyl groups were examined as the anchor moieties of sensitizing dyes for dye-sensitized solar cells by using silylazobenzene dyes. Allylsilyl and hydrosilyl dyes were observed to adsorb efficiently onto TiO₂ electrodes and the dye-adsorbed electrodes exhibited high durability to water. Light-to-electric energy conversions were also confirmed in the cells using the dye-adsorbed electrodes. The results show a high potential of allylsilyl and hydrosilyl dyes as the sensitizing dyes.

Abstract: Oxide inorganic electroluminescent device in which thin films of Pr-doped NaNbO₃ phosphor and Sb-doped SnO₂ transparent conductor are alternately stacked was prepared by sol-gel and spin-coating methods. Red electroluminescence was observed due to f-f transitions of Pr³⁺ ions by applying 5-kHz ac voltages to the device. The luminance was 1.0 cd m⁻² at 25 V ac and5.0 cd m⁻² at 34 V ac.

Abstract: La_1-xBa_xCoO₃ single crystals were grown from KOH melt at 873 K under H₂O/O₂ mixed gas flow. The grown crystals had a parallelepiped form with the edges of about 60 μm. Streaks indicating twin boundaries were observed on the surface planes of the crystals. The crystals showed magnetic anisotropy and anomalous MH hysteresis loops. The magnetocrystalline anisotropy and coupling of ferroelasticity and ferromagnetism were discussed based on the magnetic properties.

Abstract: In dye-sensitized solar cells (DSSCs) fabricated with azobenzene and azulene derivatives as the photosensitizing dyes, the replacement of the conventional I₃^-/I^- redox mediator with Br₃^-/Br^- redox mediator possessing more positive redox potential has been examined to improve open-circuit photovoltages (V_oc) of the cells. The cells with the Br₃^-/Br^- redox mediator exhibited high V_oc of ~0.8 V, resulting in higher light-to-electric energy conversion efficiencies (η) than the cells with the I₃^-/I^- redox mediator by a factor of 1.7 under the simulated sunlight irradiation (AM-1.5G, 100 mW cm^-2). The results indicate a high potential of the Br₃^-/Br^- redox mediator in DSSCs.

Abstract: In order to clarify the chemical adsorption property of allylsilane to metal-oxide surface quantitatively and to obtain the information on the reaction conditions for the efficient surface modification, chemical surface modification of nanoporous alumina membranes (NPAMs) by a typical allylsilyl compound of 4-(allyldimethylsilyl) azobenzene was examined. The chemical surface modification was performed by immersing NPAMs into the solutions of the allylsilylazobenzene. The modification was investigated precisely by estimating the amount of the silylazobenzene adsorbed on the NPAM surface using a visible absorption spectroscopy with changing the temperature, solvent, and the concentration of the solution to reveal the effects of the reaction conditions on the adsorption property of the allylsilane to the metal-oxide surface. The solutions with higher temperatures, non-polar solvents, and higher concentrations were shown to be suitable for the efficient surface modification.

Abstract: Transparent thin films of strontium titanate (SrTiO₃) were formed on the substrate of quartz glass plate by RF magnetron sputtering with changing the substrate temperatures during the sputtering from 100 to 700 °C. The particle size and the lattice constant of the cubic-SrTiO₃ crystallites composing the film were exhibited to be changed from 13 to 48 nm and from 4.02 to 3.96 Å, respectively, by the change of the substrate temperatures from 400 to 700 °C. The UV absorption edges of the transparent film samples shifted to longer wavelength with the increase of the particle size and the decrease of the lattice constant of the nanocrystalline SrTiO₃.