Optical properties of Ag–Au nanoclusters for sulphide sensing from TDDFT calculations

Abstract

A time-dependent density functional theory (TDDFT) approach is applied to investigate the optical properties of Ag–Au nanoclusters for sulphide sensing. It is found that the difference of refractive index between the cationic Ag13S and Ag13 clusters can cause the redshifts of the vertical excitation spectrum of the cationic Ag13S cluster, which is due to that sulphide can induce new electronic states in the frontier orbitals. Compared with the pure cationic Ag13 cluster, the cationic Ag12Au cluster shows enhanced sensitivity for detecting sulphide due to the hybridization between the orbitals of Ag and Au atoms, which can promote interband transition. With increasing the coverage of sulphide, more redshifts of the vertical excitation spectrum are found for the cationic Ag12Au cluster upon the adsorption of sulphide. Moreover, the cubohedral cationic Ag12Au cluster possesses more intense optical response than the icosahedral one, which is explained by the natural transition orbital analysis. It is expected that our theoretical results can provide new guidelines to design new powerful sensor for detecting sulphide using Ag–Au nanoparticles.