Thermal annealing–induced Ag/WO3/Ag plasmonic nanocavities for emission enhancement

We report a simple and effective approach to fabricate plasmonic nanocavity structures based on Ag/WO 3 /Ag multilayers by thermal annealing. Prior to nanocavity formation, the aggregation behavior of Ag films deposited on WO 3 was examined, revealing that Ag readily forms nanoparticle structures even under mild annealing conditions, with optical characteristics comparable to those of Ag nanoparticles formed on glass substrates. When applied to Ag/WO 3 /Ag multilayer structures, thermal annealing induces selective nanostructuring of the top Ag layer while preserving the flat bottom Ag mirror, leading to the formation of a nanocavity-like optical configuration. Optical measurements show that annealing reduces surface reflectance and introduces characteristic extinction features, indicating modified optical coupling within the multilayer. Photoluminescence measurements using an emissive layer deposited on the annealed structures demonstrate a pronounced enhancement of emission intensity, which strongly depends on the annealing condition. In particular, emission enhancement achieved under the selected mild annealing condition exceeds that obtained in conventional Ag nanoparticle systems. These results demonstrate that thermal annealing provides a scalable and fabrication-light route to engineer functional nanocavity-like architectures, offering a versatile platform for emission enhancement and light–matter interaction control.