Plasmonic Lattice Resonances in Highly Asymmetric Dielectric Environments

Metal-based Surface Plasmon Polariton resonances have garnered attention for their ability to confine light to sub-diffraction dimensions and enhance light-matter interactions at the nm scale across the visible and infrared (IR) spectra regime. However, these enhancements are limited by optical losses that arise from radiative coupling and absorption, which limits the quality factor (Q = λ/Δλ) of resonances. Here, we report on the narrowing of the plasmonic resonances observed experimentally in reflectance measurements of Au nanodisc lattices fabricated on a GaAs substrate when the lattice periodicity matches the wavelength for the Rayleigh anomaly in the substrate. We attribute this narrowing to the diffractive coupling of the resonators, which results in surface lattice resonances (SLRs). While SLRs are typically observed for systems with homogeneous optical environments (closely matched indices of refraction for the substrate and superstrate), our system is highly inhomogeneous (n_air = ~1, n_GaAs = ~3.4) and still supports lattice resonances. The experimental reflectivity spectra are accurately reproduced in numerical simulations. Furthermore, we couple lead chalcogenide quantum dot emitters to the nanodisc lattices and demonstrate a 3-fold increase in their photoluminescence intensity and a significant alteration of the emission line shape, in correlation with the narrow SLR. Our findings highlight the optical properties of Au nanodisc resonator arrays within a heterogeneous environment, opening new possibilities in sensing and enhanced light emission applications.