Plasmon-enhanced photoluminescence and SERS in Ag- and Au-based nanohole arrays with Ag nanoparticle decoration

Abstract

We present a comparative investigation of plasmon-enhanced photoluminescence (PL) and surface-enhanced Raman scattering (SERS) in gold and silver nanohole arrays (AuNA and AgNA) integrated within a metal-insulator-metal (MIM) configuration and further decorated with silver nanoparticles (AgNPs). The MIM architecture, composed of an Ag buffer layer, a SiO2 spacer, and a top Au or Ag nanohole film, supports strong vertical coupling of plasmonic modes confined within the dielectric gap, enabling efficient field localization and exciton-plasmon interaction. The nanostructures were fabricated via colloidal lithography and validated by finite-element simulations. AgNA exhibited stronger near-field confinement, yielding the highest absolute PL enhancement (4.93 x over glass) and pronounced SERS response of rhodamine 6G (R6G). In contrast, AuNA showed weaker absolute signals but achieved a larger relative PL gain (1.96 vs. 1.59 for AgNA) after AgNP growth, attributed to hybridization-induced redshifts improving spectral overlap with the 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)4H-pyran (DCJTB) emission. Time-resolved PL measurements revealed shortened fluorophore lifetimes for both arrays, which were further reduced by AgNP decoration, confirming enhanced radiative decay through MIM-assisted plasmon-exciton coupling. These findings elucidate the complementary roles of material damping and MIM hybridization in tuning resonance behavior and provide design insights for plasmonic and optoelectronic applications.