  An ensemble of resonance atoms is considered, which are doped into a medium
with well developed polariton effect, when in the spectrum of polariton states
there is a band gap. If an atom with a resonance frequency inside the polariton
gap is placed into the medium, the atomic spontaneous emission is suppressed.
However, a system of resonance atoms inside the polariton gap can radiate when
their coherent interaction is sufficiently strong. Thus the suppression of
spontaneous emission for a single atom can be overcome by a collective of atoms
radiating coherently. Conditions when such collective effects can appear and
their dynamics are analysed.
