Tailoring nonlinear plasmonic response of ZnSe@Ag and ZnSe@Au core–shell nanocomposites: Role of shell thickness and host matrix permittivity

This study presents a comprehensive theoretical and numerical investigation of the local field enhancement factor(LFEF) and optical bistability (OB) in zinc selenide (ZnSe)-based core–shell nanocomposites (NCs), aiming to advance their application in tunable plasmonic and photonic devices. The nanostructures are modeled as spherical ZnSe dielectric cores surrounded by metallic shells composed of either silver (Ag) or gold (Au), and embedded in various dielectric matrices including silicon dioxide (SiO2), zinc oxide (ZnO), and hafnium dioxide (HFO2) each characterized by different dielectric permittivities. Utilizing the quasi-static approximation and Lorentz–Drude formalism, we explore how variations in shell thickness (controlled by the core-to-total radius ratio) influence both the spectral and nonlinear optical responses. The results demonstrate that thicker metal shells yield stronger LFEF’s due to enhanced plasmonic confinement, especially for Ag shells, which outperform Au due to their lower damping and higher conductivity. In terms of the dielectric environment, low-permittivity matrices like SiO2 support stronger field localization, while high-permittivity matrices such as HFO2 weaken plasmonic confinement and induce a redshift in resonance peaks. Nonlinear analysis reveals that thicker shells and low-index matrices significantly enhance OB effects by lowering the switching thresholds, particularly in silver-coated systems. These findings underscore the pivotal role of shell geometry and dielectric surroundings in tailoring both linear and nonlinear plasmonic responses and provide valuable guidelines for designing NCs optimized for applications in optical sensing, photonic switching, and nano-enabled information processing.