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The photochromic properties of sputtered amorphous tungsten oxide (a-WO3−x) films have been studied. The a-WO3−x films, prepared under different oxygen partial pressures, were irradiated with ultraviolet (UV) light at room temperature, and the transmission decrease of the films was measured. We used ellipsometry for the first time with and without UV irradiation to extract the optical indices n and k of magnetron direct-current sputtered films in the VIS/IR wavelength region. We have applied for the first time the Cauchy–Lorentz model for simulating the photochromic properties of the irradiated a-WO3−x films. The results are consistent with previous reports showing that oxygen deficiency is very important in determining the photochromic properties of the a-WO3−x films.

Sol-gel processing was used to dope photochromic dyes into three matrices: metal alkoxide, metal alkoxide-polymer, and pure polymeric materials. The films on silicon and quartz substrates were examined, with and without ultraviolet (UV) irradiation, by ellipsometry, UV-visible transmission spectroscopy, and Fourier transform infrared (FTIR) transmission spectroscopy. Variable angle spectroscopic ellipsometry (VASE) data were analyzed for film thickness and optical constants, and in some cases thickness nonuniformity. A modified Cauchy and a combined Cauchy–Lorentz model were used to fit the unirradiated and irradiated film optical constants, respectively. The optical constants of the films showed significant changes upon irradiation. This means that the absorption coefficient and hence the emissivity of the films is being modulated with UV irradiation. The VASE-fitted thicknesses of the films were in the range of 1–6 μm. In the FTIR spectra, the spiropyran doped samples have shown IR transmission changes ...