  Phonons are well known to be the main mechanism for the coupling between
bright and dark excitons in nonmagnetic semiconductors. Here, we investigate
diluted magnetic semiconductors where this process is in direct competition
with the scattering at localized magnetic impurities. To this end, a recently
developed quantum kinetic description of the exciton spin dynamics in diluted
magnetic semiconductor quantum wells is extended by the scattering with
longitudinal acoustic phonons. A strong phonon impact is found in the
redistribution of exciton momenta on the exciton parabola that becomes
especially prominent for high temperatures and exciton distributions further
away from the exciton resonance which are optically dark. Despite their impact
on the energetic redistribution, acoustic phonons virtually do not affected the
exciton spin dynamics as the exciton-impurity interaction always dominates.
Furthermore, it turns out that the exciton spin lifetime increases by roughly
one order of magnitude for nonequilibrium hot exciton distributions and, in
addition, pronounced quantum kinetic signatures in the exciton spin dynamics
appearing after resonant optical excitation are drastically reduced.
