Visible and infrared photochromic properties of amorphous WO3−x films

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.