Chemistry Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
ACS Nano. 2017 Aug 22;11(8):8437-8447. doi: 10.1021/acsnano.7b04079. Epub 2017 Aug 2.
Application of colloidal semiconductor quantum dots (QDs) in optical and optoelectronic devices is often complicated by unintentional generation of extra charges, which opens fast nonradiative Auger recombination pathways whereby the recombination energy of an exciton is quickly transferred to the extra carrier(s) and ultimately dissipated as heat. Previous studies of Auger recombination have primarily focused on neutral and, more recently, negatively charged multicarrier states. Auger dynamics of positively charged species remains more poorly explored due to difficulties in creating, stabilizing, and detecting excess holes in the QDs. Here we apply photochemical doping to prepare both negatively and positively charged CdSe/CdS QDs with two distinct core/shell interfacial profiles ("sharp" versus "smooth"). Using neutral and charged QD samples we evaluate Auger lifetimes of biexcitons, negative and positive trions (an exciton with an extra electron or a hole, respectively), and multiply negatively charged excitons. Using these measurements, we demonstrate that Auger decay of both neutral and charged multicarrier states can be presented as a superposition of independent elementary three-particle Auger events. As one of the manifestations of the superposition principle, we observe that the biexciton Auger decay rate can be presented as a sum of the Auger rates for independent negative and positive trion pathways. By comparing the measurements on the QDs with the "sharp" versus "smooth" interfaces, we also find that while affecting the absolute values of Auger lifetimes, manipulation of the shape of the confinement potential does not lead to violation of the superposition principle, which still allows us to accurately predict the biexciton Auger lifetimes based on the measured negative and positive trion dynamics. These findings indicate considerable robustness of the superposition principle as applied to Auger decay of charged and neutral multicarrier states, suggesting its generality to quantum-confined nanocrystals of arbitrary compositions and complexities.
胶体半导体量子点（QD）在光学和光电设备中的应用通常因意外产生额外电荷而变得复杂，这会开启快速非辐射的俄歇复合途径，其中激子的复合能量会迅速转移到额外的载流子上，并最终以热量的形式耗散。先前的俄歇复合研究主要集中在中性和最近的带负电荷的多载流子态上。由于在 QD 中难以产生、稳定和检测多余的空穴，带正电荷的物质的俄歇动力学研究仍较为缺乏。在这里，我们应用光化学掺杂来制备具有两种不同核/壳界面轮廓（“尖锐”与“平滑”）的带负电和正电的 CdSe/CdS QD。利用中性和带电荷的 QD 样品，我们评估了双激子、负三价离子（带额外电子或空穴的激子）和多带负电荷激子的俄歇寿命。通过这些测量，我们证明了中性和带电荷的多载流子态的俄歇衰减都可以表示为独立的基本三体俄歇事件的叠加。作为叠加原理的一种表现形式，我们观察到双激子俄歇衰减速率可以表示为独立的正负三价离子途径的俄歇速率之和。通过比较“尖锐”与“平滑”界面的 QD 测量结果，我们还发现，尽管改变了俄歇寿命的绝对值，但对限制势形状的操纵并不会导致叠加原理的违反，这仍然使我们能够根据测量的正负三价离子动力学准确预测双激子俄歇寿命。这些发现表明，叠加原理在带电荷和中性多载流子态的俄歇衰减中具有相当大的稳健性，表明其适用于任意组成和复杂性的量子限制纳米晶体。
