Tungsten Trioxide Photochromic Properties

Tungsten trioxide as a transition metal oxide is an excellent photochromic material. The study found it under ultraviolet light will turn blue. And it can use in optical information storage and optical recording and other filed. Photochromic refer to compound A is subjected to the wavelength λ1 of light, can be generated product B specific chemical reaction which is different structures and spectroscopic properties. And on the other hand in the light of the wavelength λ2 or heating, products B can reversible generation compound A. The basic features of this process are: A, B under certain conditions is stable and color disparity is significant different. What’s more in the process A, B is reversible. When the energy of light which is greater than the band gap of WO₃ light on the sample, then the electron-hole pairs are generated. Photo-generated electrons into the conduction band of WO₃, and adjacent W^{6 +} combine to generate W^{5 +}. At the same time electron holes can react with water molecule which is adsorbed on the sample surface, weakening the water molecules bond H-O, caused by the decomposition of water molecules, generating protons. Proton release into the WO₃ then is become blue H₂WO₃ which is tungsten bronze.

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