Experimentelle Physik 2, Technische Universität Dortmund , 44221 Dortmund, Germany.
State Key Laboratory of Precision Spectroscopy, East China Normal University , Shanghai 200062, China.
Nano Lett. 2017 May 10;17(5):2844-2851. doi: 10.1021/acs.nanolett.6b05305. Epub 2017 Apr 7.
The optical properties of colloidal semiconductor nanocrystals are largely influenced by the trapping of charge carriers on the nanocrystal surface. Different concentrations of electron and hole traps and different rates of their capture to the traps provide dynamical charging of otherwise neutral nanocrystals. We study the photocharging formation and evolution dynamics in CdS colloidal quantum dots with native oleic acid surface ligands. A time-resolved technique with three laser pulses (pump, orientation, and probe) is developed to monitor the photocharging dynamics with picosecond resolution on wide time scales ranging from picoseconds to milliseconds. The detection is based on measuring the coherent spin dynamics of electrons, allowing us to distinguish the type of carrier in the QD core (electron or hole). We find that although initially negative photocharging happens because of fast hole trapping, it eventually evolves to positive photocharging due to electron trapping and hole detrapping. The positive photocharging lasts up to hundreds of microseconds at room temperature. These findings give insight into the photocharging process and provide valuable information for understanding the mechanisms responsible for the emission blinking in colloidal nanostructures.
胶体半导体纳米晶体的光学性质在很大程度上受到载流子在纳米晶体表面上的捕获的影响。不同浓度的电子和空穴陷阱以及它们被陷阱捕获的不同速率为原本中性的纳米晶体提供了动态充电。我们研究了具有天然油酸表面配体的 CdS 胶体量子点中的光电荷形成和演化动力学。开发了一种具有三个激光脉冲（泵浦、取向和探测）的时间分辨技术，以皮秒分辨率在从皮秒到毫秒的宽时间范围内监测光电荷动力学。检测基于测量电子的相干自旋动力学，使我们能够区分 QD 核中的载流子类型（电子或空穴）。我们发现，尽管最初由于快速的空穴捕获而发生负光电荷，但由于电子捕获和空穴脱陷，它最终演变为正光电荷。在室温下，正光电荷可持续长达数百微秒。这些发现深入了解了光电荷过程，并为理解胶体纳米结构中发射闪烁的机制提供了有价值的信息。
