Influence of dopants Cu, Ga, In, Hg on the electronic structure of CdnSn (n = 6, 15) clusters – a DFT study

Abstract

The influence of doping metal ions on the structural, electronic and optical properties of Cd_n−yX_yS_n (n = 6, 15; y = 1, 2, 4) clusters is systematically studied using DFT and TD-DFT studies. Among the dopants, Cu²⁺ and In²⁺ slightly distort the structure of Cd_nS_n clusters, though they have a strong bonding interaction with S²⁻ however; another two dopants Ga²⁺ and Hg²⁺ significantly distort the cluster's structure. Molecular composition analysis reveals the dopants not only contribute to the optically active states, but also to the surface or trap states. The HOMO–LUMO gap is significantly reduced for Cu²⁺, Ga²⁺, and In²⁺ dopants. However, for Hg²⁺ the gap is meagerly affected. In large clusters, Cd₁₅S₁₅, the polarizability values decrease on doping, though individual dopants show a nonlinear pattern. The absorption spectra of doped CdS clusters are generally red shifted though a few Ga and In clusters exhibit a blue shift due to the Burstein–Moss effect.