Photocarrier dynamics in anatase TiO 2 : Evidence of thermally activated collisions between carriers
Résumé
The photoluminescence emission spectrum at low temperature of the TiO2 anatase shows a broad band around 2.3 eV that has been largely attributed to self-trapped excitons. In this paper, time-resolved experiments conducted at low temperature on a thin layer and a single crystal give insights into the carrier dynamics inside TiO2. The decay of the photoluminescence with time can be described by a single power law from the picoseconds time range up to the milliseconds time range. The decay rate increases with increasing temperature. We propose to interpret these observations by a collision mechanism between self-trapped excitons that diffuse via hopping processes. These excitons, which are stabilized by the indirect band gap of anatase
TiO2, can be ionized at higher temperatures and lead thus to an acceleration of the observed dynamics.