Plasmonic Copper Nanocubes Coupled to a Film for Near-Infrared Fluorescence Enhancement

Cu nanocubes have been found to support a strong and narrow localized surface plasmon resonance (LSPR) but are restrained by limited spectral tunability. In this study, a film-coupled Cu nanocube system is designed and systematically studied using finite-difference time-domain based numerical simulations. Because of the coupling between the Cu nanocube and the underlying film, a plasmonic cavity mode is generated and featured by a spectrally tunable LSPR and an intense near field. By tailoring the resonance to the near-infrared (NIR) wavelength region, we demonstrate that the film-coupled Cu nanocube system supports a large NIR fluorescence emission enhancement owing to the strong excitation rate enhancement and the quantum efficiency enhancement. The knowledge obtained in this study can guide future design of low-cost Cu-based optical devices.