Non-Monotonic Size-Dependent Exciton Radiative Lifetime in CsPbBr3 Nanocrystals

TL;DR

This study reveals a non-monotonic relationship between size and exciton radiative lifetime in CsPbBr3 nanocrystals, influenced by quantum confinement and state populations, informing tailored optical material design.

Contribution

It uncovers the size-dependent non-monotonic behavior of radiative lifetime in CsPbBr3 nanocrystals, highlighting the roles of quantum confinement and state populations.

Findings

Large nanocrystals have long lifetimes due to dim states.

Small nanocrystals also show long lifetimes due to reduced oscillator strength.

Intermediate-sized nanocrystals have the shortest radiative lifetime.

Abstract

Lead-halide perovskite nanocrystals have recently emerged as desirable optical materials for applications such as coherent quantum light emitters and solid-state laser cooling due to their short radiative lifetime and near-unity photoluminescence quantum yield. Here, we investigate the effect of CsPbBr3 nanocrystal size on the radiative lifetime under ambient conditions. High-quality nanocrystals, with monoexponential time-resolved photoluminescence decay behaviors, unveil a non-monotonic trend in radiative lifetime. This non-monotonicity appears to reflect a behavior common among II-VI (CdSe) and perovskites semiconducting nanocrystals. We find that large nanocrystals in the weak quantum confinement regime exhibit long radiative lifetimes due to a thermally accessible population of dim states. Small nanocrystals within the strong quantum confinement regime, surprisingly, also show long radiative lifetimes, due however to a substantial reduction in oscillator strength. Nanocrystals in the intermediate quantum confinement regime displays the shortest radiative lifetime, as their oscillator strength is enhanced relative to particles in the strong confinement regime, but do not have sufficient low-lying dim states like the large particles to counteract this affect. These findings shed light on the impact of nanocrystal size on radiative lifetime and pave the way for tailored optical materials in various optical applications.