Photoluminescence of Cr-doped TiO2 induced by intense UV laser excitation

Nanocrystalline anatase (A) and rutile (R) TiO2 were synthesized by the thermal hydrolysis and then were surface doped with Cr ions by adsorption. The samples were characterized by X-ray diffraction, X-ray fluorescence, Raman spectroscopy, optical absorption and photoluminescence (PL) methods. It is found that the PL emission and optical absorption near the band gap edge occur with the same electronic transitions in TiO2. The Cr3+ doping leads to the blue and red shifts of the PL peaks in A/Cr TiO2 due to the Burstein-Moss and band tailing effects, respectively. The Auger type non-radiative recombination in R/Cr TiO2 quenches the PL emission intensity. For anatase samples at low concentrations of Cr ions (0.5 at%) the PL emission increases compared to the undoped A TiO2 due to the formation of additional radiative recombination centers. At higher contents of Cr (1.0 at%), the PL intensity decreases due to the concentration quenching effect. (C) 2015 Published by Elsevier B.V.