Rossi Daniel, Qiao Tian, Liu Xiaohan, Khurana Mohit, Akimov Alexey V, Cheon Jinwoo, Son Dong Hee
Center for NanoMedicine, Institute for Basic Science (IBS), Seoul 03722, South Korea.
Department of Chemistry, Texas A&M University, College Station, Texas 777843, USA.
J Chem Phys. 2020 Nov 14;153(18):184703. doi: 10.1063/5.0027972.
The fine structure of the band edge exciton and the dark exciton photoluminescence (PL) are topics of significant interest in the research of semiconducting metal halide perovskite nanocrystals, with several conflicting reports on the level ordering of the bright and dark states and the accessibility of the emitting dark states. Recently, we observed the intense dark exciton PL in strongly confined CsPbBr nanocrystals at cryogenic temperatures, in contrast to weakly confined nanocrystals lacking dark exciton PL, which was explained by the confinement enhanced bright-dark exciton splitting. In this work, we investigated the size-dependence of the dark exciton photoluminescence properties in CsPbBr and CsPbI quantum dots in the strongly confined regime, showing the clear role of confinement in determining the bright-dark energy splitting (ΔE) and the dark exciton lifetime (τ). We observe the increase in both ΔE and τ with increasing quantum confinement in CsPbBr and CsPbI QDs, consistent with the earlier predictions on the size-dependence of ΔE and τ. Our results show that quantum confinement plays a crucial role in determining the accessibility to the dark exciton PL and its characteristics in metal halide perovskite nanocrystals.
在半导体金属卤化物钙钛矿纳米晶体的研究中，带边激子和暗激子光致发光（PL）的精细结构是备受关注的课题，关于亮态和暗态的能级排序以及发射暗态的可及性存在若干相互矛盾的报道。最近，我们在低温下观察到强受限CsPbBr纳米晶体中强烈的暗激子PL，与之形成对比的是，缺乏暗激子PL的弱受限纳米晶体，这可通过受限增强的亮 - 暗激子分裂来解释。在这项工作中，我们研究了强受限区域内CsPbBr和CsPbI量子点中暗激子光致发光特性的尺寸依赖性，揭示了受限在确定亮 - 暗能量分裂（ΔE）和暗激子寿命（τ）方面的明确作用。我们观察到在CsPbBr和CsPbI量子点中，随着量子限域的增加，ΔE和τ均增大，这与先前关于ΔE和τ尺寸依赖性的预测一致。我们的结果表明，量子限域在决定金属卤化物钙钛矿纳米晶体中暗激子PL的可及性及其特性方面起着关键作用。
