  The recombination dynamics and spin polarization of excitons in CdSe
nanocrystals synthesized in a glass matrix are investigated using polarized
photoluminescence in high magnetic fields up to 30 Tesla. The dynamics are
accelerated by increasing temperature and magnetic field, confirming the dark
exciton nature of the low-temperature photoluminescence (PL). The circularly
polarized PL in magnetic fields reveals several unusual appearances: (i) a
spectral dependence of the polarization degree, (ii) its low saturation value,
and (iii) a stronger intensity of the Zeeman component which is higher in
energy. The latter feature is the most surprising being in contradiction with
the thermal population of the exciton spin sublevels. The same contradiction
was previously observed in the ensemble of wet-chemically synthesized CdSe
nanocrystals, but was not understood. We present a theory which explains all
the observed features and shows that the inverted ordering of the circular
polarized PL maxima from the ensemble of nanocrystals is a result of
competition between the zero phonon (ZPL) and one optical phonon (1PL) assisted
emission of the dark excitons. The essential aspects of the theoretical model
are different polarization properties of the dark exciton emission via ZPL and
1PL recombination channels and the inhomogeneous broadening of the PL spectrum
from the ensemble of nanocrystals exceeding the optical phonon energy.
