Quantized Auger recombination of biexcitons in CdSe nanorods studied by time-resolved photoluminescence and transient-absorption spectroscopy

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We studied the recombination dynamics of biexcitons in elongated CdSe nanocrystals (nanorods) usingtime-resolved photoluminescence (PL) and transient absorption (TA) spectroscopy. The decay times of the PLand TA signals decrease with increasing nanorod length. Under weak excitation, the PL decay is faster thanthe TA decay, and the nonradiative hole trapping determines the PL decay in several hundreds of picoseconds.Under intense excitation, the PL decay curves are similar to the TA decay curves, and the rapid biexciton decay iscaused by nonradiative Auger recombination. A clear correlation is observed between the Auger recombinationcoefficient of the biexcitons and the average PL lifetime of the single excitons.Moreover, theAuger recombinationlifetimes of the biexcitons are shorter in nanorods than in spherical nanocrystals of the same volume. Our studyclarified that the Auger recombination rate is strongly affected by a high surface-state density.
2011-04-27