Origin of Optical Excitations in Fluorine-Doped Titania from Response Function Theory: Relevance to Photocatalysis

We investigate the effect of fluorine doping on the optical spectra of stoichiometric and reduced TiO2 anatase, brookite, and rutile using density functional methods. The present approach is able to reproduce the main features of experiments and high-level quasiparticle calculations for undoped titania but at a much lower computational cost, thus allowing the study of doped titania, which requires large supercells. Whereas the simulated spectra of F-substituted brookite and rutile do not show any significant new feature, a relatively intense new band near the visible region is predicted for F-substituted anatase. This allows one to suggest assigning the spectral features near the visible region, observed on multiphase F-doped titania samples, to the presence of anatase. The physical origin of the new absorption band in F-doped anatase is unambiguously attributed to the presence of Ti3+ centers.