Design rules for plasmon-enhanced rare-earth luminescence in metal core–shell nanoparticles

Abstract Plasmon-enhanced luminescence in metal–dielectric core–shell nanoparticles (NPs) is a promising strategy for biosensing and photonic applications, yet the optimal geometric parameters remain poorly constrained. Here, we perform a systematic numerical study based on the boundary element method to identify the NP diameter and dielectric shell thickness that maximize rare-earth ion luminescence in Ag- and Au-based core–shell systems. We show that, while the optimal core diameter depends on the metal and excitation wavelength, the optimal shell thickness is universal across all studied configurations within our sweep. Analysis of the spatial decay of the near field reveals a size-dependent transition from dipolar to multipolar plasmonic behavior, which governs both the enhancement magnitude and its spatial extent. Silver-based configurations outperform gold in both peak enhancement and near-field intensity under the respective optima. These results establish practical design rules for plasmon-enhanced luminescent nanocomposites and clarify the electromagnetic mechanisms underlying size-dependent enhancement.