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

Abstract

Eu 3 + -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°C, respectively. Photoluminescence (PL) properties were investigated under the excitation of 325nm He–Cd laser. Visible PL peaking at 543, 598, 620, 665, and 694nm are founded which are ascribed to D15→F17, D05→Fj7(j=1,2,3,4) transitions of Eu3+ ions and the PL intensities reach maximum when the sample was heat treated at 700°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°C, the PL intensity of Eu3+ ions decreases obviously, while near-infrared PL (815nm) 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.