Nonlinear differential ultrafast laser absorption spectroscopy observation of charge carrier dynamics of CdSxSe1-x nanocrystal doped glasses

摘要

Based on femtosecond transient absorption spectroscopy, the charge carrier dynamics of CdSxSe1-x nanocrystal doped glasses was investigated by analyzing the nonlinear differential transient absorption spectra. Time constants were extracted, which are different from the literature results using similar samples: they are pump laser intensity-dependent and decrease with increasing pump laser intensity, whereas risetime constants are pump laser intensity-independent and high-order exciton recombination can be identified from the spectra. The threshold pump intensity was determined, which is lower than the literature result. Reasons for high-order recombination were analyzed, and broad size, state distribution and high pump intensity are found as key factors. Auger recombination may play a key role in the multi-exciton recombination. Theoretical calculations and analysis support this conclusion. A schematic model for electron transport and the formation of triexcitons in our samples are proposed to explain these results.