Visible and near-infrared photoluminescences of europium-doped titania film

Eu3+-doped TiO2 films were prepared on silicon substrates by sol-gel method. Anatase and rutile phases appear when the samples were heat treated in oxygen atmosphere at 500 and 900 degrees C, respectively. Photoluminescence (PL) properties were investigated under the excitation of 325 nm He-Cd laser. Visible PL peaking at 543, 598, 620, 665, and 694 nm are founded which are ascribed to D-5(1)-> F-7(1), D-5(0)-> F-7(j)(j=1,2,3,4) transitions of Eu3+ ions and the PL intensities reach maximum when the sample was heat treated at 700 degrees C. Compared with the PL spectra of pure TiO2, energy transfer from self-trapped exciton state to rare-earth ions is considered to exist in Eu3+-doped TiO2 system. After the sample was heat treated at higher temperatures than 700 degrees C, the PL intensity of Eu3+ ions decreases obviously, while near-infrared PL (815 nm) was detected which is due to the defect states associated with Ti3+ ions. Through the analysis of excitation and emission mechanism, we conclude that visible and near-infrared PLs are two competitive processes and energy back transfer from Eu3+ ions to TiO2 host is responsible for the decrease of visible PL intensity and the increase of near-infrared PL intensity. (c) 2006 American Institute of Physics.