  In this paper, polarized photoluminescence caused by exciton
quasi-equilibrium spin orientation on Zeeman sublevels in an ensemble of
quantum dots of different sizes is theoretically studied. It is found that: (i)
the splitting of the photoluminescence bands in a magnetic field in an ensemble
of quantum dots is several orders of magnitude larger than the Zeeman splitting
of exciton levels in a single dot, (ii) the sign of the circular polarization
of the photoluminescence changes along the contour of the bands, (iii) the
change of the sign of the polarization is associated with the change of the
sign of the exciton g-factor. A universal formula for the dependence of the
exciton g-factor on the quantum dot size is obtained. This dependence is valid
for both bulk material and nanostructures of different types and sizes.
Comparison of the results obtained with the experimentally measured data has
been carried out.
