When blinking helps: enhanced single-photon purity in the off states of perovskite quantum dots

Abstract

Photoluminescence blinking typically degrades the single-photon purity of quantum dot emission. Here, we show that individual CsPbBr${}_3$ perovskite quantum dots (PQDs) can exhibit the opposite behavior: low-emitting off states are dimmer and shorter-lived, yet more strongly antibunched than high-intensity on states. Using time-correlated single-photon counting combined with state-resolved second-order correlation analysis, we identify a subset of PQDs in which the zero-delay second-order correlation, $g_0^{(2)}$, decreases upon switching from the on state to the off state, indicating improved single-photon purity. In the most pronounced case, $g_0^{(2)}$ decreases from 0.23 in the on state to 0.08 in the off state. We attribute this counterintuitive behavior to self-trapped-exciton-mediated suppression of the biexciton--exciton cascade, which suppresses multiphoton emission more effectively than single-exciton emission. These findings reveal an unconventional blinking regime in PQDs and show that blinking does not necessarily degrade single-photon purity.

8 pages, 6 figures. This version of the manuscript was revised and updated after reviewers' comments from previous submission (IOP Reports on Progress in Physics), now submitted to Phys. Rev. Lett