Dual-mode temperature sensor based on metal-dielectric-metal nanocavity

Surface plasmon resonance (SPR) is a highly sensitive optical phenomenon that exhibits a strong response to changes in the surrounding dielectric environment. Variations in the refractive index of the medium adjacent to a metal film lead to shifts in the resonance frequency. By monitoring changes in the SPR peak, interactions between the metal film surface and the environment can be detected. In this study, we designed a temperature sensor based on a metal-dielectric-metal (MDM) nanocavity structure. Leveraging the linear relationship between temperature and refractive index, we numerically simulated the transmission characteristics of the structure using the finite-difference time-domain (FDTD) method. The results reveal three resonance peaks in the absorption spectrum. Through structural parameter optimization, perfect absorption rates of 98.8%, 98.9%, and 96.1% were achieved at these three wavelengths, respectively. These resonance peaks demonstrate high sensitivity to changes in the refractive index of the sensing material, with sensitivities of 0.1, 0.275, and 0.3125 nm/°C, respectively. Additionally, changes in the refractive index were found to alter the local electric field intensity. Temperature measurement was further realized based on the relationship between the upconversion fluorescence enhancement factor and the localized field strength. Dual-mode sensing of local temperature or environmental changes was achieved by monitoring both spectral shifts and variations in upconversion fluorescence intensity. This work proposes a novel strategy for the design and application of new nanoscale temperature sensors and contributes to the promotion of high-performance composite upconversion nanomaterials.