Fluorescence quenching by a metal nanoparticle in the extreme near-field regime

We study the spontaneous decay rate of a dipole emitter close to a metallic nanoparticle in the extreme near-field regime. The metal is modeled using a nonlocal dielectric function that accounts for the microscopic length scales of the free electron gas. We describe quantitatively the crossover between the macroscopic and microscopic regimes and the enhanced nonradiative decay due to microscopic interactions. Our theory is in agreement with results previously established in the asymptotic near- and far-field regimes.