Kamisaka Hideyuki, Kilina Svetlana V, Yamashita Koichi, Prezhdo Oleg V
Department of Chemistry, University of Washington, Seattle, Washington 98195, USA.
Nano Lett. 2006 Oct;6(10):2295-300. doi: 10.1021/nl0617383.
Vibrationally induced pure-dephasing of electronic states in PbSe quantum dots (QDs) at room temperature is investigated using two independent theoretical approaches based on the optical response function and semiclassical formalisms. Both approaches predict dephasing times of around 10 fs and reproduce the recently measured homogeneous linewidths of optical absorption well. Because dephasing slows down with increasing cluster size, the dephasing times calculated for the small clusters correspond to the lower end of the experimental data. The dephasing is almost independent of the electronic excitation energy and occurs faster for biexcitons than single excitons. The dephasing time is roughly proportional to the square root of the mass of the lighter atom (Se), suggesting that dephasing should be faster in PbS and slower in PbTe relative to PbSe. Core atoms produce stronger dephasing than surface atoms. In the collective description, pure-dephasing occurs via low-frequency acoustic modes, in support of the elastic QD model of dephasing. Because the electron-phonon coupling in PbSe QDs is relatively weak compared to other semiconductor nanocrystals, fast vibrationally induced dephasing can be expected in semiconductor QDs in general.
利用基于光学响应函数和半经典形式的两种独立理论方法，研究了室温下PbSe量子点（QD）中电子态的振动诱导纯退相。两种方法都预测退相时间约为10飞秒，并很好地再现了最近测量的光吸收均匀线宽。由于退相随着团簇尺寸的增加而减慢，为小团簇计算的退相时间对应于实验数据的下限。退相几乎与电子激发能无关，双激子的退相比单激子更快。退相时间大致与较轻原子（Se）质量的平方根成正比，这表明相对于PbSe，PbS中的退相应该更快，而PbTe中的退相应该更慢。核心原子比表面原子产生更强的退相。在集体描述中，纯退相通过低频声学模式发生，这支持了退相的弹性量子点模型。由于与其他半导体纳米晶体相比，PbSe量子点中的电子-声子耦合相对较弱，因此一般可以预期半导体量子点中会有快速的振动诱导退相。
