Tungsten trioxide is a photochromic material that may be applied for producing thermal insulation film. And therefore it may be widely applied to manufacture a variety of heat-insulating glass window, heat-insulating glass door, and the like. This kind of thermal insulation film has high heat resistance, weather resistance and transmittance of visible light.
Since the photochromism of the amorphous tungsten trioxide film was first reported in 1973, the tungsten trioxide photochromic material has received much attention. And extensive research on this thermal insulation has been conducted.
Based on a large number of experimental studies, the predecessors have conducted extensive discussions and speculations on the mechanism of photochromism of tungsten trioxide, and two models have been formed, including the double-charge injection/extraction model and the small-pole model. The widely accepted mechanism of discoloration is the dual-charge injection/extraction model. And the discoloration in this model is due to the interband transitions of electrons.
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