Carrier-assisted recombination in anatase TiO2

Differential optical transmission experiments performed on TiO2 layers reveal a carrier population decay that follows a power-law over several orders of magnitude in both time and signal amplitude, across a temperature range from 10 K up to room temperature. The exponent of the power-law is fractional, increasing linearly at low temperatures before following an activation law above 160 K. We propose a mechanism based on collision-assisted recombination, where self-trapped excitons are first delocalized and then partially ionized into free polarons as the temperature increases, giving rise to the acceleration of the population decay.