Dielectric Functions of Semiconductor Nanoparticles from the Optical Absorption Spectrum: The Case of CdSe and CdS

We propose a new method to extract the complete size-dependent complex dielectric function ε(E) of semiconductor nanoparticles (NPs) from spectroscopic data. Typical experimental absorption spectra are available in a limited energy range near the absorption edge. We show that this limitation can be overcome by matching the NP dielectric function with the bulk dielectric function at high energies beyond the experimental range. Thus, using the Kramers−Krönig relations that link the real and imaginary parts, it is possible to extract the complete ε(E) of the NP. This is achieved through an iterative procedure that systematically improves the trial ε(E) until the absorption spectrum of the NP is accurately reproduced in the experimental range. Here we describe the methodology and we obtain the ε(E) of CdSe and CdS NPs of selected sizes from published data sets.

本研究提出一种全新方法，可从光谱数据中提取半导体纳米颗粒（nanoparticles，简称NPs）的完整尺寸相关复介电函数ε(E)。典型实验吸收光谱仅能覆盖吸收边附近的有限能量区间。本研究表明，通过将纳米颗粒的介电函数与实验能量范围之外的高能区体相介电函数进行匹配，可克服这一局限。因此，借助连接实部与虚部的克拉默斯-克勒尼希（Kramers−Krönig）关系，即可提取得到纳米颗粒完整的ε(E)。该方法通过迭代过程实现：对试算的ε(E)进行系统性优化，直至在实验能量区间内准确复现纳米颗粒的吸收光谱。本文详细阐述该方法，并从已公开数据集当中提取得到特定尺寸的硒化镉（CdSe）与硫化镉（CdS）纳米颗粒的ε(E)。