Fluorescence quenching by plasmonic nanoantennas

Generalizing a previously developed analytical model of metal-enhanced fluorescence to the case of the strong coupling between a quantum emitter and a plasmonic nanoantenna, we study the fluorescence quenching in the strong coupling regime. When the nanoantenna is a simple Ag sphere and the quantum emitter approaches to its surface the fluorescence turns suppressed (both dipole and quadrupole moments of the system vanish) in the whole spectral range. However, if the nanoantenna is a plasmonic dimer with a tiny gap between two plasmonic nanoparticles, and the coupling grows due to the increase of the emitter dipole moment, the fluorescence quenching never occurs. This unexpected result explains why the nanolaser regime can be achieved with these nanoantennas, whereas a simple nanosphere coupled to quantum emitters can be a spaser.