Femtosecond nonlinear transmission techniques are applied to study mechanisms for optical nonlinearities and ultrafast carrier dynamics in CdS nanocrystals (NC's). The obtained data indicate the change in a dominant hole relaxation channel at high pump levels where nonlinear recombination effects start to play a significant role. This is manifested as a distinct difference in nonlinear-optical responses measured at low and high pump intensities in quasiequilibrium at long times after excitation. The analysis of the wavelength and time dependence of the nonlinear transmission over a wide pump-intensity range shows clearly that this difference is due to an Auger-process-assisted trapping of holes at surface/interface-related states. This trapping leads to efficient charge separation and the generation of a dc electric field that modifies the nonlinear optical response in NC's at high pump intensities.
|Number of pages||7|
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - May 15 1997|
ASJC Scopus subject areas
- Condensed Matter Physics