Carrier recombination dynamics in anatase TiO2 nanoparticles

We present an experimental study of the radiative recombinationdynamics in size-controlled TiO2nanoparticles in the range 20–130 nm. Time-integrated photoluminescence spectra clearly show a dominance of self-trapped exciton (STE) emission, with main features not dependent on the nanoparticle size and on its environment. From picosecond time-resolved experiments as a function of the excitation density and the nanoparticle size we address the STE recombinationdynamics as the result of two main processes related to the direct STE formation and to the indirect STE formation mediated by non-radiative surface states.