Study of photoluminescence and electronic states in nanophase strontium titanate

Nanophase strontium titanate specimens were prepared by a stearic acid sol- gel process. The phase structures, photoluminescence, and electron states w ere investigated by X-ray diffraction and fluorescence spectroscopy. A visi ble emission band centered at 500 nm was observed in the nanosized particle s under an excitation with energy lower than the band gap at room temperatu re. The peak intensity of the visible emission band increases with decreasi ng particle size. This visible emission is attributed to the recombination of the long-lived self-trapped excitons with forceful binding-energy formed in the nanosized SrTiO3 mediated by the localized levels which are correla ted to the intrinsic surface states and defect centers via a strong electro n-phonon interaction. The dependence of the visible emission band on excita tion wavelength was examined under both room and liquid nitrogen temperatur es where there exist a series of levels of the self-trapped excitons within the forbidden gap and the properties of the self-trapped states are closel y related to temperature.