Optical Absorption Coefficient and Refractive-Index Change in a Coupled Quantum Dot-Metallic Nanoparticle Structure

Abstract

In the present work, we investigate the problem of the optical absorption coefficient (OAC) and refractive-index change (RIC) in a semiconductor quantum dot placed in the vicinity of a spherical metallic nanoparticle. We derive the total OAC and RIC from the density-matrix equations through different approaches, one without approximations and the other keeping only linear and third-order nonlinear terms. The derived formulae are then applied in a specific hybrid nanostructure to calculate the OAC and RIC. The results obtained from the derived formulae are used to compare cases of various interparticle distance values and applied light intensities and find that, although for specific distances and intensities the formulae may give similar results, in general, they give different results. Moreover, it becomes clear that the distance between the quantum dot and the metallic nanoparticle, in combination with the polarisation of the light field, plays a significant role in the OAC and RIC of the quantum dot. Expressly, conditional on the polarisation of the applied electric field, the OAC and RIC of the quantum dot can be either enhanced or suppressed close to the metallic nanoparticle compared to their values in the absence of the metallic nanoparticle.