Photoluminescence kinetics and dynamics in semiconductor nanocrystals

Summary form only given. Single molecule confocal microscopy has been used to investigate the detailed kinetics of fluorescence intermittency in colloidal II-VI (CdSe) semiconductor quantum dots. Two distinct modes of behavior are observed corresponding to (i) sustained "on" episodes (/spl square//sub on/) of rapid laser absorption/fluorescence cycling, followed by (ii) sustained "off" episodes (/spl square//sub off/) where essentially no light is emitted despite continuous laser excitation. Both the on-time and off-time probability densities follow an inverse power law, P(/spl square//sub on/off/) /spl square/ 1//spl square//sub on/off//sup m/, over more than seven decades in probability density and five decades in time. Such inverse power law behavior is an unambiguous signature of highly distributed rates (over 10/sup 5/-fold) as opposed to isolated rate processes between sparse "on" and "off" configurations of the system. The large dynamic range of the current data also permits several models of fluorescence intermittency to be critically evaluated. The inverse power law in P(/spl square//sub on/) excludes any model based on a static configuration of trap sites, and the results highlight the crucial role of fluctuations in the QD environment. Finally, we offer a simple model based on the dynamic tunneling of carriers through fluctuating barriers, which suggests an alternate way to characterize blinking kinetics.