  The modified density of optical states due to a weak coupling with external
cavities or other resonant matter (Purcell effect), can also be recast as the
effect of coherent superposition of the classical paths of the photon. When the
coupling is stronger, the quantum interference of additional paths representing
the possible re-absorption of the photon from the excited proximal matter, also
plays a significant role in the radiative decay of the emitter. The effect of
these additional non-classical paths of the photon on the density of radiative
and non-radiative states, is included using a proposed simple modification to
the weak coupling model. This effect is especially evident in the anomalous
enhancements of spontaneous emission due to extremely small fully absorbing
metal nanoparticles less than 10 nm in dimensions. Incorporating multiple
emitters and such very small metal nanoparticles coupled to each other, the
large contribution of non-classical paths to radiative states in such bulk
materials is elucidated.
