Spectral properties of intermediate to high refractive index nanocubes

Abstract

Plasmonic resonances in sub-wavelength cavities, created by metallic nanocubes separated from a metallic surface by a dielectric gap, lead to strong light confinement and strong Purcell effect, with many applications in spectroscopy, enhanced light emission and optomechanics. However, the limited choice of metals, and the constraints on the sizes of the nanocubes, restrict the optical wavelength range of applications. We show that dielectric nanocubes made of intermediate to high refractive index materials exhibit similar but significantly blue shifted and enriched optical responses due to the interaction between gap plasmonic modes and internal modes. This result is explained, and the efficiency of dielectric nanocubes for light absorption and spontaneous emission is quantified by comparing the optical response and induced fluorescence enhancement of nanocubes made of barium titanate, tungsten trioxide, gallium phosphide, silicon, silver and rhodium.