Temperature dependence of photoluminescence, Raman scattering, and transmittance spectra of anatase Ti_1-xFe_xO₂ nanocrystalline films

Anatase Ti_1-xFe_xO₂ (x=0, 1%, 2%) nanocrystalline films were prepared on quartz substrates by a facile nonhydrolytic sol-gel route. The structure and optical properties have been studied by X-ray diffraction (XRD), Raman scattering, transmittance spectra and temperature dependent photoluminescence (PL). The B_1g, E_g and (A_1g+B_1g) modes of anatase phase TiO₂ can be observed in Raman spectra. Dielectric functions have been extracted by fitting the transmittance spectra in the photon energy range of 0.5-6.5 eV with Adachi's model. The pure TiO₂ film displays a strong broadening visible luminescence band; however, Fe-doped samples exhibit a very weak luminescence due to the increase of oxygen vacancy concentration in TiO ₂. With the temperature increases, the PL intensity decreases monotonously and there are five emission peaks for the pure sample in low temperatures, which could be attributed to oxygen vacancies, surface states and F⁺ center.