Search for oxides showing visible-light active photochromism and visible-induced structural change by Raman Spectroscopy.

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The purpose of this study is to search for oxides showing structural changes or photochromisms under illumination of safe and cheap visible lights and to elucidate mechanisms of the phenomena. It was elucidated that the Y-based high-tc superconductor YBa_2Cu_3O_x underwent change in its structure upon visible-light illumination and that vanadium oxide V2Os exhibited visible-light photochromism-In this year, the light-switching process and the reversibility of these materials have been inestigated in details1.Light-induced structural change and light-switching process in YBa_2Cu_3aO_xIt was elucidated that when Raman spectra of YBa_2Cu_3O_x single crystals were measured under illumination of green laser with a wave length of 515nm, the intensities for defect-induced modes corresponding to CuO chains decreased with time and it was transfered to a metastable state. This state was recovered to the original state upon the illumination of a laser with a wavelength of 900nm. It has turned out that the light-induced structural change can occur reversibly by use of two different lights and it can be used as a light switch.2. Evaluation of the reversibility of visible-Light photochromism in vanadium oxidePolycrystalline V_2O_5 turns blue-black upon irradiation with visible laser light (515nm) in air due to photo reduction of V^<5+> The coloration was diminished when heated at 400℃, and the coloration-decoloration cycle was repeatable. In order to evaluate the reversibility of the visible-light photochromism in V_2O_5. photo luminescence (PL) spectra were measured. The sample was repeatedly irradiated and heated without irradiation. The PL intensity recovers during the rest upon heating and decays consistently during irradiation. This cycle can be repeated without significant degradation of the photochromic effect.