Influence of TiCl4 treatment on surface defect photoluminescence in pure and mixed-phase nanocrystalline TiO2.

Room-temperature UV-excited photoluminescence spectra are reported for nanocrystalline films of anatase, rutile, and mixed-phase TiO2 (Degussa P25) before and after treatment with TiCl4 solution. The surface defect luminescence of anatase in the visible region is suppressed by TiCl4 treatment, indicating a decrease in surface traps. A similar anatase surface-defect emission is observed in the mixed-phase nanoparticles but is completely quenched following TiCl4 treatment and replaced by emission characteristic of rutile. Our results suggest that TiCl4 treatment of mixed-phase TiO2 may result in a surface layer of rutile and that radiative recombination of electron-hole pairs formed in the bulk anatase region of nanocrystallites occurs after electrons migrate to newly formed rutile surfaces.