Excitation and emission enhancement of single molecule fluorescence through multiple surface-plasmon resonances on metal trimer nanoantennas.

We study theoretically the light scattering from trimers of metal nanowires, with emphasis on the occurrence of multiple surface-plasmon resonances, showing that such resonances can be exploited to achieve twofold-enhanced fluorescence from a single molecule placed in the nanotrimer gaps, even if excitation and emission frequencies are separated. Pump enhancement stems from the local field enhancement coinciding with one of the resonances, whereas a strong enhancement of the radiative decay rate (and quantum yield) is revealed at a different resonance, leading to a large overall signal emission.