Plasmon Enhancement Reveals Origin of the Dark States of Photoluminescence Intermittency in Quantum Dots

Dark states of photoluminescence (PL) intermittency in colloidal quantum dots (QDs) interrupt PL emission and significantly reduce emission intensity, severely hindering QD applications. However, the origin of dark states remains ambiguous due to their extremely low intensity, which impedes the development of effective suppression strategies. In this study, we use plasmonic gold nanoparticles to significantly increase the radiative rate of excitons, and thereby enhancing the dark-state PL intensity. Calculations of radiative rate scaling based on the dark-state PL intensity and lifetime reveal that the dark states originate from band-edge carrier trapping by collectively activated nonradiative multiple recombination centers (MRCs). Transition states that accompany the dark states are frequently observed in PL trajectories, revealing the presence of a positive feedback mechanism for the activation and deactivation of nonradiative MRCs induced by the phonon kick effect. We perform a Monte Carlo simulation to model the dark and transition states and quantify the nonradiative rates involved. Understanding the origin of dark states can contribute to their suppression, optimization of synthesis, and improvement of performance in QD-based applications.