Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, United States.
ACS Nano. 2012 Jul 24;6(7):6515-24. doi: 10.1021/nn302371q. Epub 2012 Jul 11.
Understanding the pathways of hot exciton relaxation in photoexcited semiconductor nanocrystals, also called quantum dots (QDs), is of paramount importance in multiple energy, electronics and biological applications. An important nonradiative relaxation channel originates from the nonadiabatic (NA) coupling of electronic degrees of freedom to nuclear vibrations, which in QDs depend on the confinement effects and complicated surface chemistry. To elucidate the role of surface ligands in relaxation processes of nanocrystals, we study the dynamics of the NA exciton relaxation in Cd(33)Se(33) semiconductor quantum dots passivated by either trimethylphosphine oxide or methylamine ligands using explicit time-dependent modeling. The large extent of hybridization between electronic states of quantum dot and ligand molecules is found to strongly facilitate exciton relaxation. Our computational results for the ligand contributions to the exciton relaxation and electronic energy-loss in small clusters are further extrapolated to larger quantum dots.
理解光激发半导体纳米晶体（也称为量子点）中热激子弛豫的途径在多个能源、电子和生物应用中至关重要。一个重要的非辐射弛豫通道源自电子自由度与核振动的非绝热（NA）耦合，在量子点中，这取决于限制效应和复杂的表面化学。为了阐明表面配体在纳米晶体弛豫过程中的作用，我们使用显式的时间相关模型研究了由三甲基氧化膦或甲胺配体钝化的 Cd(33)Se(33)半导体量子点中 NA 激子弛豫的动力学。发现量子点和配体分子的电子态之间的强杂化程度极大地促进了激子弛豫。我们对小分子团簇中配体对激子弛豫和电子能量损失贡献的计算结果进一步外推到较大的量子点。
