PL spectra of the 5.0% Eu-doped titania nanoparticles. (a) Before and (b) after thermal annealing (left). Schematic illustration of the possible mechanism of energy transfer from the TiO2 host to Eu+3 (right). VB, CB, and DS correspond to the valence band, conduction band, and defect state, respectively.
Pal et al. Nanoscale Research Letters 2012 7:1 doi:10.1186/1556-276X-7-1