Effects of Local Dielectric Environment on Single-Molecule Spectroscopy of a CdSe/CdS Core/Shell Quantum Dot

This work studies effects of local dielectric environment on both a single exciton and high-order excitons in a single CdSe/CdS core/shell quantum dot (QD) with nearly ideal photoluminescence (PL) properties. For typical single-molecule spectroscopy measurements, isolated QDs embedded in a thin polymer layer (subwavelength thickness) are deposited on top of a glass slide. This results in a spatial dependence on the dielectric environment of the QDs along the vertical direction. PL peak positions of single-exciton and negative trion (two electrons and one hole) states of a single QD are barely affected by the local dielectric environment, which can be applied as indicators of size distribution of the ensemble and the size of a specific QD. Other PL properties of single excitons and high-order excitons, including PL intensity of single excitons, PL quantum yield of trions and biexcitons, monoexponential radiative decay lifetimes of all states studied, and Auger recombination lifetimes of high-order excitons, are all found to be sensitive to the local dielectric environment. Furthermore, by removing the heterogeneous dielectric environment, all spectroscopic properties of single QDs are found to well correlate with the ensemble measurements.