The utilization of excited charge carriers in semiconductor nanocrystals (NCs) for optoelectronic technologies has been a long-standing goal in the field of nanoscience. Experimental efforts to extend the lifetime of excited carriers have therefore been a principal focus. To understand the limits of these lifetimes, in this work, we theoretically study the time scales of pure electron relaxation in negatively charged NCs composed of two prototypical materials: CdSe and CdS. We find that hot electrons in CdSe have lifetimes that are 5 to 6 orders of magnitude longer than in CdS when the relaxation is governed only by the intrinsic properties of the materials. Although these two materials are known to have somewhat different electronic structure, we elucidate how this enormous difference in lifetimes arises from relatively small quantitative differences in electronic energy gaps and phonon frequencies, as well as the crucial role of Fröhlich-type electron–phonon couplings.

中文翻译：

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与 CdS 相比，CdSe 纳米晶体中热电子的本质冷却速度较慢


在半导体纳米晶体 （NC） 中利用激发的载流子进行光电技术一直是纳米科学领域的长期目标。因此，延长激发子寿命的实验工作一直是主要重点。为了了解这些寿命的极限，在这项工作中，我们从理论上研究了由两种原型材料组成的带负电荷的 NC 中纯电子弛豫的时间尺度：CdSe 和 CdS。我们发现，当弛豫仅由材料的本征性质控制时，CdSe 中的热电子的寿命比 CdS 长 5 到 6 个数量级。尽管已知这两种材料具有略有不同的电子结构，但我们阐明了这种巨大的寿命差异是如何从电子能隙和声子频率的相对较小的定量差异以及 Fröhlich 型电子-声子耦合的关键作用引起的。