Effect of fluorine doping and SiO2 under-layer on the optical properties of TiO2 thin films

Fluorine-doped TiO2 thin films were prepared via sol–gel method. Optical constants were obtained by fitting theoretical UV–Vis transmittance spectra to experimental ones within Forouhi–Bloomer dispersion model. The results show that doping with fluorine does not affect the absorption edge of TiO2 films. The linear part of the absorption edge for the films on SiO2/soda lime substrate is red shifted in comparison with that on bare soda lime and a broadened ‘tail’ up to ∼ 2.7 eV is observed. It is attributed to additional localized states within the TiO2 band gap introduced by structural defects in titania lattice originated from TiO2/SiO2 interface.