Spectral Analysis for Photon Emission of Rare-Earth Ions in Single Plasmonic Hot Spot

Rare earth ion luminescent materials have attracted extensive attention due to their wide applications in biochemical sensing and bioimaging. However, the low quantum yield and weak luminescence intensity have restricted their further development. Realizing the modulation of rare-earth ions' emission behavior has become a hot topic in the interdisciplinary fields of materials and chemometrics. Herein, the regulation of the electron decay process and emission of photon signals of rare earth ion (Eu³⁺) has been achieved in a well-defined plasmonic nanocavity. This nanocavity consists of Ag shell-isolated nanoparticles (SHINs) and an ultraflat Au film, which are separated by a polymer dielectric spacer and CaF₂:Eu³⁺ nanoparticles. Contrary to the intrinsic photoluminescence of CaF₂:Eu³⁺, a factor of 408 increase in the spontaneous emission rate and simultaneously an 800-fold enhancement in the emission intensity have been realized in nanocavities via comprehensive spectroscopic analysis. Additionally, the evolution law between the plasmon resonances and the luminescent enhancement as well as the emission spectrum of Eu³⁺ indicates a highly effective modulation of emission behavior by plasmons. This presents a novel strategy for enhancing the performance of optical micro- and nanodevices based on rare-earth ion materials, demonstrating significant potential in applications such as bioimaging and surface detection analysis.