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

TL;DR

This paper explains the cause of dark states in quantum dots using plasmon enhancement, which could help improve their performance in applications.

Contribution

The study identifies the origin of dark states in quantum dots as nonradiative multiple recombination centers activated by phonon kicks.

Findings

Dark states in quantum dots originate from band-edge carrier trapping by nonradiative multiple recombination centers.

Plasmonic gold nanoparticles enhance dark-state photoluminescence intensity, enabling clearer observation.

A Monte Carlo simulation models dark and transition states, quantifying nonradiative rates.

Abstract

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.

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