  A general formalism to describe the dynamics of quantum emitters in
structured reservoirs is introduced. As an application, we investigate the
optical coherence of an atom-like emitter diagonally coupled via a link-boson
to a structured bosonic reservoir and obtain unconventional dephasing dynamics
due to non-Markovian quantum feedback for different temperatures. For a
two-level emitter embedded in a phonon cavity preservation of finite coherence
is predicted up to room temperature.
