Photochromism of doped and undoped WO3 sol-gel films: Determination and analysis of optical constants

Photochromic films are those characterized by the ability to undergo optical changes in response to photo stimulation. Thus, they have various technological applications, such as, for example, in displays or sensing devices. As a result, these films are currently generating great scientific interest. A grid of materials widely used for this purpose are transition metal oxides, among which, due to their properties, WO3 stands out, being selected to be studied in this work. To produce thin films of WO3 and WO3X (X = Ti, Nb, Ta and Zr), the solutions were prepared through the sol-gel process. Then, following the dip-coating technique, these solutions were deposited on a glass substrate. The average thickness provided to the films was found around 320 nm. For the analyses, the variations in the optical transmission spectra caused by illumination with sunlight for 60 min, were obtained. With the characterization of the films, through the transmittance spectra in the colored and decolored states, according to the envelope method, their refractive index, dielectric constant and band gap could be calculated, in addition to their chromatic properties.