Photochromic Properties of TiO2: Doping Effect

TiO2 is one of the most extensively studied photoactive materials, serving as both a photocatalyst and a photochromic agent. Improving photochromic properties involves not only increasing the intensity of photocoloring but also improving the rates of coloring and bleaching, as well as the cyclicity of the process. This can be achieved by modifying the material’s structure through methods such as doping, phase transformations, etc. The doping process was conducted by exposing a low-temperature plasma generated from an underwater diaphragm discharge to a TiO2 sol. The precursors of the doping elements were electrode materials (Mo, Nb, and W wires). The phase composition and structure of the synthesized sol, both before and after plasma treatment, were analyzed using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The results of the structural-phase analysis indicated that titanium dioxide was present in the brookite phase. XPS analysis revealed that during the doping process, metal ions in various oxidation states (+4, +5, and +6) were incorporated into the TiO2 structure. Spectrophotometric studies of the irradiated samples demonstrated that the doping process enhances the photochromic characteristics of TiO2. The influence of the dopant material on the intensity and rate of coloration was also observed. Factors contributing to the improvement of photochromic characteristics were examined.