  We present an analytical model for plasmonic enhancement of metal
photoluminescence (MPL) in metal nanostructures with characteristic size below
the diffraction limit. In such systems, the primary mechanism of MPL
enhancement is excitation of localized surface plasmons (LSP) by recombining
carriers followed by a photon emission due to LSP radiative decay. For
plasmonic nanostructures of arbitrary shape, we obtain a universal expression
for MPL Purcell factor that describes the plasmonic enhancement of MPL in terms
of metal dielectric function, LSP frequency, and the system volume. We find
that the lineshape of MPL spectrum is affected by the interference between
direct carrier recombination processes and those mediated by plasmonic antenna
which leads to a blueshift of MPL spectral band relative to LSP resonance in
scattering spectra observed in numerous experiments.
