The spontaneous emission of a single molecule is substantially modified close to a metallic
nanostructure. We study the spectral behavior of the radiative and nonradiative decay rates
and of the local-field factor in the vicinity of a plasmon resonance. We show that the highest
fluorescence enhancement is obtained for an emission wavelength redshifted from the
plasmon resonance, and that quenching always dominates at plasmon resonance. These
results may have experimental implications in spectroscopy and monitoring of elementary …