Effect of heat treatment on the UV-vis-NIR and PL spectra of TiO2 films

TiO2 films fabricated by DC reactive magnetron sputtering on quartz glass substrates were annealed in several different ways. The structure and properties of the films were characterized by UV-vis-NIR, PL spectra and X-ray photoelectron spectroscopy. For the annealed samples, it is interesting that a clear absorption peak was found at 496 nm. The analysis of XPS spectra shows that oxygen can diffuse outward from the lattice, resulting in production of Ti3+ and oxygen vacancies. The PL spectra show that the absorption peak at 496 nm is not induced by a transition within the forbidden band gap. Combining the XPS results with the linear combination of atomic orbital molecular orbital (LCAO-MO) theory and crystal-field (CF) theory, we can explain the appearance of this absorption peak. We conclude that the spectroscopic features result from the t2g*−eg* electronic transition in these TiO2 films.