Structure and luminescence properties of TiO2:Er3+ nanocrystals annealed at different temperatures

Erbium doped TiO₂ nanocrystals with the structures of anatase, pyrochlore Er₂Ti₂O₇, and rutile, characterized by X-ray diffraction, have been obtained at different annealing temperatures from 300 °C to 900 °C. The nanocrystalline size for anatase TiO₂ is reduced with increasing doped erbium concentration. Following ultraviolet 325 nm irradiation, the intensity of the green emission is the most intense for the TiO₂:Er³⁺ nanocrystals with a structure of pyrochlore Er₂Ti₂O₇, which evolves from the structure of anatase annealed at 800 °C. Moreover, following ultraviolet 325 nm and infrared 980 nm irradiation, the visible emission spectra for the nanocrystals annealed at 900 °C change drastically. Correspondingly, the structure of anatase disappears, while that of rutile becomes dominant, which indicates that phase transformation occurs.