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.