Structure-Related Optical Fingerprints in the Absorption Spectra of Colloidal Quantum Dots: Random Alloy vs. Core/Shell Systems

TL;DR

This paper demonstrates that optical absorption spectra can distinguish between random alloy and core/shell quantum dots, providing a simple experimental method for structural identification without advanced tools.

Contribution

The study introduces a computational approach using exact-disorder tight-binding calculations to differentiate alloy and core/shell quantum dots based on their optical spectra.

Findings

Optical spectra reveal distinguishable features for alloy vs. core/shell structures.

Method applies to Cd(Se,S) and (Zn,Cd)(Se,S) quantum dots with zincblende structure.

Approach requires no additional free parameters beyond bulk properties.

Abstract

We argue that the experimentally easily accessible optical absorption spectrum can often be used to distinguish between a random alloy phase and a stoichiometrically equivalent core/shell realization of ensembles of monodisperse colloidal semiconductor quantum dots without the need for more advanced structural characterization tools. Our proof-of-concept is performed by conceptually straightforward exact-disorder tight-binding calculations. The underlying stochastical tight-binding scheme only parametrizes bulk band structure properties and does not employ additional free parameters to calculate the optical absorption spectrum, which is an easily accessible experimental property. The method is applied to selected realizations of type-I Cd(Se,S) and type-II (Zn,Cd)(Se,S) alloyed quantum dots with an underlying zincblende crystal structure and the corresponding core/shell counterparts.