The reversible UV-laser-light-induced spectral change and origin of the 2.4Â eV luminescence band in SrTiO3

In order to clarify the origin of the 2.4 eV luminescence band in SrTiO3, as-grown and annealed SrTiO3 single crystals are irradiated with a continuous-wave ultraviolet laser light (λ=325nm) in different atmospheres at room temperature. Under the laser light irradiation in a vacuum, the 2.4 eV luminescence band grows with increasing irradiation time, while it returns to the original weak-luminescence state under the same laser light irradiation in oxygen gas. The excitation-intensity, temperature and time dependences of the photoluminescence spectra are also measured for the crystals. All the results indicate that the 2.4 eV luminescence band arises not from intrinsic self-trapped excitons but from extrinsic excitons trapped around oxygen defects. Near-band-edge emissions have been observed, for the first time, at 3.2 and 2.9 eV under intense excitation.