Time-resolved study of self-trapped exciton luminescence in anatase TiO2 under two-photon excitation

We have studied the dynamics of photocarriers in anatase phase of TiO2 with time-resolved spectroscopy of self-trapped exciton (STE) luminescence. It is found that the decay curve of luminescence under one-photon excitation well above the band gap energy shows power-law behavior, suggesting that spatial separation of an electron-hole pair occurs under interband excitation. A similar result is obtained under two-photon excitation. We conclude that the carrier separation is ascribed to intrinsic dynamical properties of photocarriers in anatase. It is inferred that the carrier separation occurs during energy relaxation towards the band bottom. Temperature dependence of the decay curve is also discussed in terms of thermal dissociation of STEs.