Photophysical Study of Electron and Hole Trapping in TiO2 and TiO2/Au Nanoparticles through a Selective Electron Injection

Abstract

The photophysics surrounding the electron and hole trapping in TiO2 do not have a scientific consensus. Herein, we studied the steady-state photoluminescence and time-resolved spectroscopy features from TiO2 and TiO2/Au nanoparticles (NPs). In TiO2/Au NPs, time-resolved photoluminescence indicates that the electrons from bandgap excitation decay slower (∼30 ps) than in TiO2 (<24 ps). We conclude this as a result of the band bending passivation effect on the surface electron traps. Meanwhile, electron trapping is proved as the dominant surface depopulation process because of the easy-fill characteristics of surface hole traps even under low excitation density, which also interprets the slow surface hole trapping (∼2 ns) in TiO2. Through plasmon-assisted electron injection, we distinguished the electron and hole behaviors at varied photon fluences and then obtained the intrinsic bulk trapping of electrons and holes in the ∼50 and ∼400 ps time range, respectively.