Colloidal semiconductor quantum dots have received significant interest and attention due to their increased photostability, tunable, sharp, and bright emission profiles and their solution processability. For these reasons, they have been used as phosphors in displays and as probes for bioimaging. These applications require tuning the radiative and nonradiative rates such that radiative recombination dominates. This is often achieved by addition of an epitaxial shell to reduce the nonradiative rate. Addition of a shell also directly impacts the radiative rate. For this reason, understanding the radiative rate upon shell growth is of interest. Previous studies have primarily treated the core and shell material statically in determining the excited state properties. By combining temperature-dependent transient photoluminescence measurements with atomistic simulations we demonstrate that nuclear fluctuations within the quantum dot can significantly alter the radiative rate in CdSe/CdS quantum dots. We show that nuclear fluctuations can result in local and transient trapping of primarily the electron close to the interface between the core and the shell materials. This results in a decrease of the radiative rate, which we show to be dependent on both the core and shell dimensions of the quantum dot. These findings are significant because it suggests that fluctuations can play a significant role in determining excited state properties of quantum dots and suggests that a statistical treatment is necessary to fully capture excited state dynamics in colloidal quantum dots.

Effect of fluctuations on excited state rates in core/shell quantum dots

253rd National Meeting (2017)

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