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...