The role of surface charges in the blinking mechanisms and quantum-confined Stark effect of single colloidal quantum dots

Abstract

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.