Surface plasmon on the metal nanosphere excitation by a quantum   oscillator
  Surface waves on a metal nanosphere are described in terms of quantum electrodynamics. The interaction of surface waves with a quantum oscillator is discussed in the dipole approximation. The increase in the spontaneous emission rate of the excited quantum oscillator, the so called Purcell factor, is evaluated to exceed in several orders that of in vacuum. 
A. M. Leontovich, V. V. Lidsky
physics.optics