Picosecond photoluminescence and transient absorption in silicon nanocrystals

We report on picosecond photoluminescence decay in silicon nanocrystals prepared by ion implantation. We found that the photoluminescence within the first nanosecond after photoexcitation by a 5320.3em0exnm picosecond pulse differs substantially from that with 266∕3550.3em0exnm excitation. The former has a broad spectrum including the anti-Stokes region, a quadratically pump-dependent amplitude, and a decay time of 1050.3em0exps. The latter scales linearly with the pump and has a 11000.3em0exps decay time. We observed also a quadratic pump scaling of the slow component in the transient absorption dynamics. We interpret our data in terms of different conditions at low and large excitation excess energy, and by the Auger recombination of carriers in nanocrystals containing two photoexcited electron-hole pairs.