Photoexcited carrier dynamics in potassium tantalate

Relaxation processes of photoexcited carriers have been studied in KTaO3. The excitation above the absorption band edge generates a broad luminescence with a large Stokes shift, suggesting the formation of self-trapped excitons. The luminescence decay is found to be non-exponential, indicating the broad distribution of the carrier lifetime. The decay obeys power law after 10 ms, whose exponent becomes steeper as the temperature increases. The mean lifetime of the luminescence is as long as 10 ms at 4.6 K, and becomes faster at high temperatures. The temperature dependence of the lifetime should come from the thermally activated hopping motion of localized electrons and holes. Localized carriers may play an important role in the giant photoinduced dielectricity in KTaO3.