Photoluminescence in anatase titanium dioxide nanocrystals

Titanium dioxide (TiO2) nanocrystals were prepared by a hydrolysis process of tetrabutyl titanate. X-ray diffraction and Raman scattering showed that the as-prepared TiO2 nanocrystals have anatase structure of TiO2, and that the monophase anatase nanocrystals can be achieved through a series of annealing treatments below 650 degrees C. We measured photoluminescence (PL) spectra of the TiO2 nanocrystals. Under 2.41-2.71 eV laser irradiation, the TiO2 nanocrystals displayed strong visible light emission with maxima of 2.15-2.29 eV even at excitation power as low as 0.06 W/cm(2) To identify the PL mechanism in the TiO2 nanocrystals, the dependences of the PL intensity on excitation power and irradiation time were investigated. The experimental results indicated that the radiative recombination is mediated by localized levels related to surface defects residing in TiO2 nanocrystallites.