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.

Twist provides a new degree of freedom for nanomaterial modifications, which can provide novel physical properties. Here, colloidal two-dimensional (2D) twisted CdSe nanoplatelets (NPLs) are successfully fabricated and their morphology can change from totally flat to edge-twisted, and then to middle-twisted with prolonged reaction time. By combining experiments and corresponding theoretical analyses, we have established the length-dependent relationships between the surface energy and twist, with a critical lateral dimension of 30 nm. We found that the defects formed during the synthesis process play a vital role in generating intense stress that develops a strong torsion tensor around the edges, resulting in edge-twisted and final middle-twisted NPLs. Furthermore, due to the geometric asymmetry of twisted NPLs, the dissymmetry factor of single particle NPLs can reach up to 0.334. Specifically, quantum coupling occurs in middle-twisted NPLs by twisting one parent NPL into two daughter NPLs, which are structurally and electronically coupled. This work not only further deepens our understanding of the twist mechanism of 2D NPLs during colloidal synthesis, but also opens a pathway for applications using twistronics and quantum technology.

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.