  We study the exciton magnetic polaron (EMP) formation in (Cd,Mn)Se/(Cd,Mg)Se
diluted-magnetic-semiconductor quantum wells using time-resolved
photoluminescence (PL). The magnetic field and temperature dependencies of this
dynamics allow us to separate the non-magnetic and magnetic contributions to
the exciton localization. We deduce the EMP energy of 14 meV, which is in
agreement with time-integrated measurements based on selective excitation and
the magnetic field dependence of the PL circular polarization degree. The
polaron formation time of 500 ps is significantly longer than the corresponding
values reported earlier. We propose that this behavior is related to strong
self-localization of the EMP, accompanied with a squeezing of the heavy-hole
envelope wavefunction. This conclusion is also supported by the decrease of the
exciton lifetime from 600 ps to 200 - 400 ps with increasing magnetic field and
temperature.
