Hot-Carrier Relaxation Within CdSe/CdS Core/Shell Nanoplatelets

We present time-resolved photoluminescence spectroscopy of a series of colloidal CdSe/CdS core/shell nanoplatelets with different core and shell thicknesses. Carrier numbers are determined from the integrated photoluminescence intensities, and carrier temperatures are determined from the high-energy exponential tail on the photoluminescence spectra. For times between 10 ps and 1 ns and for shell thicknesses up to 4 monolayers, the measured carrier relaxation dynamics are well described by a simple model of Auger reheating: biexcitonic Auger recombination continually increases the average energy of the carriers (while decreasing their number), and this reheating sets a bottleneck to cooling through electron-phonon coupling. For times between 1 and 10 ps, the relaxation dynamics are consistent with electron-phonon coupling, where the bottleneck is now the decay of the LO-phonon population. For shell thicknesses greater than 4 monolayers, the simple Auger-reheating model cannot quantitatively account for the measurement results. The implications of these results will be presented.