Nano Tungsten Oxide Films Photochromic Properties

In the role of external excitation source, a substance or a system has undergone significant changes in the color of the phenomenon known as discoloration. When the photochromic compound A subject refers to a certain wavelength of light irradiation, the photochemical reaction can occur to give the product B, color A and B is significantly different. B irradiation or by heating the additional beam of light can be restored to its original form A. Photochromic (Photochromism) is occurring under the action of a light reversible chemical reactions. As a transition metal oxide, tungsten oxide film is an excellent photochromic material, the study found tungsten oxide under UV light will turn blue. Because photochromic properties of tungsten oxide in the optical information storage, optical control, optical switches, field optics materials, optical information such as genetic material has broad application prospects and attracted much attention.

Photochromic effect mechanism of nano tungsten oxide film photochromic tungsten oxide accompanied by reversible oxidation - reduction reactions, discoloration mechanism available now widely recognized in 1975 by Faughnan proposed double charge injection / extraction model to explain that in the ultraviolet Under irradiation, valence band electrons are excited into the conduction band, and generates electron-hole pairs photogenerated electrons are then W (VI) to capture, generate W (V), while reducing species photogenerated holes or interior surface oxide film generating proton H +, implanted inside the film, and the reduced oxides generated blue tungsten bronze HxWO3, blue as a result of W (V) in the valence band electrons into the W (VI) conduction band transitions. W6 (A) + W5 (B) <=> W5 (A) + W6 (B), due to the above change does not disrupt the crystalline structure of the material, and therefore the oxidation of the photochromic effect with good reversibility and fatigue tungsten material performance.

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