Abstract
Excitons in colloidal semiconductor nanoplatelets (NPLs) are weakly confined in the lateral dimensions. This results in significantly smaller Auger rates and, consequently, larger biexciton quantum yields, when compared to spherical quantum dots (QDs). Here we report a study of the temperature dependence of the biexciton Auger rate in individual CdSe/CdS core–shell NPLs, through the measurement of time-gated second-order photon correlations in the photoluminescence. We also utilize this method to directly estimate the single-exciton radiative rate. We find that whereas the radiative lifetime of NPLs increases with temperature, the Auger lifetime is almost temperature-independent. Our findings suggest that Auger recombination in NPLs is qualitatively similar to that of semiconductor quantum wells. Time-gated photon correlation measurements offer the unique ability to study multiphoton emission events, while excluding effects of competing fast processes, and can provide significant insight into the photophysics of a variety of nanocrystal multiphoton emitters.
Highlights
Excitons in colloidal semiconductor nanoplatelets (NPLs) are weakly confined in the lateral dimensions
NPLs exhibit sharper absorption and emission peaks, a larger absorption cross section, directed emission, and a shorter radiative lifetime[6−10] compared with their 0D and 1D counterparts. These properties allow for promising lasing media, as low gain threshold lasing media,[5,11−13] and are determined in part by the dynamics of multiple excited (MX) states
In spherical quantum dots (QDs), because of the strong quantum confinement, the Auger rate is an order of magnitude higher than the radiative rate
Summary
Excitons in colloidal semiconductor nanoplatelets (NPLs) are weakly confined in the lateral dimensions. Combining measurements of g(2)(0) with selection of photon detections according to their arrival times provide us a route to extracting the rate of Auger recombination, which limits the BXQY in NPLs.[19] notably, in this time-gated g(2)(τ), the measured value of the Auger rate is indifferent to the existence of single-exciton nonradiative pathways and is significantly less sensitive to the intermittent nature of PL in colloidal nanocrystals (NC blinking).
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