Colloidal semiconductor quantum dots (QDs) exhibit broadband light absorption, continuously tunable narrowband emission, and high photoluminescence quantum yields. As such, they represent promising materials for use in light-emitting diodes, solar cells, detectors, and lasers. Single-QD spectroscopy can remove the ensemble averaging to reveal the diverse optical properties and exciton dynamics of QD materials at the single-particle level. The results of relevant research can serve as guidelines for materials science community in tailoring the synthesis of QDs to develop novel applications. This paper reviews recent progress in exciton dynamics revealed by single-QD spectroscopy, focusing on the exciton and multi-exciton dynamics of single colloidal CdSe-based QDs and perovskite QDs. Finally, potential future directions for single-QD spectroscopy and exciton dynamics are briefly considered.

The two frequently observed phenomena, photoluminescence (PL) blinking and quantum-confined Stark effect (QCSE)-induced spectral diffusion, are not conducive to the applications of colloidal quantum dots (QDs). It remains elusive how these two phenomena are linked to each other. Unraveling the potential link between blinking and QCSE could facilitate the adoption of appropriate strategies that can simultaneously suppress both PL blinking and spectral diffusion. In this work, we investigated the blinking mechanism and QCSE of single CdSe/CdS/ZnS QDs in the presence of positive and negative surface charges using single-dot PL spectroscopy. We found that the negative surface charges can simultaneously suppress PL blinking and spectral diffusion of single QDs. On the other hand, the positive surface charges could change the blinking mechanisms of QDs from Auger-blinking to band-edge carrier (BC)-blinking. Two types of QCSE were observed, and a significant QCSE-induced spectral broadening of 5.25 nm was measured, which could be attributed to the hopping of surface charges between different surface-trap sites. Based on these findings, several theoretical models are proposed to explain various phenomena observed.