Colouration of tungsten oxide films: A model for optically active coatings

The chromogenism of optically active tungsten oxide film coatings is investigated. The chemical composition and the structure of tungsten oxide films deposited by evaporation are analyzed. Various coloration procedures and the most probable models describing the change in optical densities are discussed. The proportionality of W5+ to the coloration and the different channels for reversible chromogenic coloration are given. Chromogenic behavior of coatings is observed for a broad spectrum of materials, and various mechanisms are responsible for the changes in the optical properties in the visible wavelength range. The various mechanisms, reactions, and processes of optically active coatings are demonstrated on the tungsten oxide films.