Hoffman Maxwell P, Lee Autumn Y, Nagelj Nejc, Lee Youjin V, Olshansky Jacob H
Department of Chemistry, Amherst College Amherst MA 01002 USA
Department of Chemistry, University of California, Berkeley Berkeley CA USA.
RSC Adv. 2021 Nov 4;11(57):35887-35892. doi: 10.1039/d1ra07556j.
Computational models have been developed that can accurately predict the electronic structure and thus optical properties of a variety of quantum dot (QD) materials. However, the application of these models to core/shell and other heterostructured QDs has received less experimental corroboration owing to the difficulty in systematically synthesizing and characterizing large ranges of geometries. In the current work, we synthesized a library of core/shell CdSe/CdS QDs with varying core sizes and shell thicknesses, and have characterized their radiative recombination rates. We find that the core size has only a modest effect on the radiative recombination rates, far less than is predicted by conventional effective mass models. In order to theoretically describe the experimental data, we performed an empirical modification of an effective mass model. We find that the conduction band offset between CdSe and CdS must be empirically altered based on QD core size in order to match our experimental data. This is hypothesized to be a result of reduced interfacial strain in core/shell QDs with smaller cores. The resultant relationship between conduction band offset and core size is used to create a predictive map of radiative lifetime as a function of core size and shell thickness. This map will be useful to researchers implementing CdSe/CdS core/shell QDs for a variety of applications since it can provide geometry specific excited state lifetimes.
已经开发出了能够准确预测各种量子点（QD）材料的电子结构进而光学性质的计算模型。然而，由于难以系统地合成和表征大范围的几何结构，这些模型在核壳及其他异质结构量子点中的应用得到的实验验证较少。在当前工作中，我们合成了一系列具有不同核尺寸和壳层厚度的核壳CdSe/CdS量子点库，并对它们的辐射复合率进行了表征。我们发现核尺寸对辐射复合率的影响较小，远小于传统有效质量模型的预测。为了从理论上描述实验数据，我们对有效质量模型进行了经验修正。我们发现，为了匹配我们的实验数据，CdSe和CdS之间的导带偏移必须根据量子点核尺寸进行经验性改变。据推测，这是由于核尺寸较小的核壳量子点中界面应变减小所致。导带偏移与核尺寸之间的所得关系被用于创建辐射寿命作为核尺寸和壳层厚度函数的预测图。该图对将CdSe/CdS核壳量子点用于各种应用的研究人员将很有用，因为它可以提供特定几何结构的激发态寿命。
