Vonk Sander J W, Rabouw Freddy T
Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 1, 3584 CC Utrecht, The Netherlands.
J Phys Chem Lett. 2023 Jun 15;14(23):5353-5361. doi: 10.1021/acs.jpclett.3c00437. Epub 2023 Jun 5.
Experiments on single colloidal quantum dots (QDs) have revealed temporal fluctuations in the emission efficiency of the single-exciton state. These fluctuations, often termed "blinking", are caused by opening/closing of charge-carrier traps and/or charging/discharging of the QD. In the regime of optical excitation, multiexciton states are formed. The emission efficiencies of multiexcitons are lower because of Auger processes, but a quantitative characterization is challenging. Here, we quantify fluctuations of the biexciton efficiency for single CdSe/CdS/ZnS core-shell QDs. We find that the biexciton efficiency "blinks" significantly. The additional electron due to charging of a QD accelerates Auger recombination by a factor of 2 compared to the neutral biexciton, while opening/closing of a charge-carrier trap leads to an increase of the nonradiative recombination rate by a factor of 4. To understand the fast rate of trap-assisted recombination, we propose a revised model for trap-assisted recombination based on reversible trapping. Finally, we discuss the implications of biexciton blinking for lasing applications.
对单个胶体量子点（QD）的实验揭示了单激子态发射效率的时间波动。这些波动通常被称为“闪烁”，是由电荷载流子陷阱的打开/关闭和/或量子点的充电/放电引起的。在光激发 regime 中，会形成多激子态。由于俄歇过程，多激子的发射效率较低，但定量表征具有挑战性。在这里，我们量化了单个 CdSe/CdS/ZnS 核壳量子点双激子效率的波动。我们发现双激子效率会显著“闪烁”。与中性双激子相比，量子点充电产生的额外电子会使俄歇复合加速 2 倍，而电荷载流子陷阱的打开/关闭会使非辐射复合率增加 4 倍。为了理解陷阱辅助复合的快速速率，我们提出了一种基于可逆捕获的陷阱辅助复合修正模型。最后，我们讨论了双激子闪烁对激光应用的影响。
