Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States.
ACS Nano. 2010 Oct 26;4(10):5994-6000. doi: 10.1021/nn101357q.
Using time-resolved photoluminescence spectroscopy, we analyze single and multiexciton emission energies and decay dynamics of CdS/ZnSe core/shell nanocrystals (NCs). The NCs exhibit a characteristic type-II band alignment that leads to spatially separated charges; this effect is at the origin of long radiative exciton lifetimes, repulsive biexciton interaction energies, and reduced Auger recombination efficiencies. We determine these properties as a function of ZnSe shell thickness and find that the exciton emission energies and the decay times depend little on this parameter. In contrast, the spectral and dynamic properties of biexcitons vary strongly with the shell thickness. The considerable shell dependence of the biexciton decay lets us conclude that the associated Auger process involves the excitation of holes localized in the ZnSe shell. In NCs with thick shells, the large blue shift of the biexciton emission energy is mainly caused by Coulomb repulsion between electrons localized in the CdS core. The different sensitivity of exciton and multiexciton characteristics on the ZnSe shell thickness provides a unique opportunity to tune them independently.
利用时间分辨光致发光光谱，我们分析了 CdS/ZnSe 核/壳纳米晶体（NCs）的单激子和多激子发射能量和衰减动力学。NCs 表现出特征的 II 型能带排列，导致电荷空间分离；这种效应是长辐射激子寿命、排斥双激子相互作用能和降低的俄歇复合效率的起源。我们确定了这些特性作为 ZnSe 壳厚度的函数，并发现激子发射能量和衰减时间对此参数的依赖性很小。相比之下，双激子的光谱和动态特性随壳层厚度强烈变化。双激子衰减的相当大的壳依赖性使我们得出结论，相关的俄歇过程涉及到局域在 ZnSe 壳中的空穴的激发。在具有厚壳的 NCs 中，双激子发射能量的大蓝移主要是由局域在 CdS 核中的电子之间的库仑斥力引起的。激子和多激子特性对 ZnSe 壳厚度的不同敏感性为它们的独立调节提供了独特的机会。
