Enhanced spontaneous emission rate in annular plasmonic nanocavities

The spontaneous emission rate of erbium ions is enhanced by coupling to localized plasmonic resonances in subwavelength annular apertures in a Au film. The Er³⁺ ions, embedded in SiO₂, are selectively located inside the apertures. The annular apertures act as nanocavities, enhancing the local density of optical states at the Er emission wavelength of 1.54 μm when the cavities are tuned to that wavelength. We show that this leads to an eightfold increase of the photoluminescence intensity, in conjunction with a 2.4-fold enhancement of the spontaneous emission rate.