A significant increase in carrier concentration in TiO₂ by Sm doping

Sm-doped TiO 2 thin films were synthesized by pulsed laser deposition. The luminescence and donor-generation properties of thin films annealed at various temperatures were investigated. The results showed that Sm-related emissions occurred in the temperature range 500 °C–800 °C. The donor densities in this temperature range were two orders of magnitude higher than that of the undoped TiO 2 thin film. The effect of annealing within the temperature window indicates a local fine structural transition of the ligands around Sm 3+ ions from T d symmetry to the lower C 4v one; these ions are effective luminescence centers in TiO 2 :Sm thin films. This local structural distortion also increases defect generation, and this increases the donor density in the same temperature region.