  We report on the experimental and theoretical studies of optical alignment
and optical orientation effects in an ensemble of core/shell CdSe/CdS colloidal
nanoplatelets. The dependences of three Stokes parameters on the magnetic field
applied in the Faraday geometry are measured under continuous wave resonant
excitation of the exciton photoluminescence. Theoretical model is developed to
take into account both bright and dark exciton states in the case of strong
electron and hole exchange interaction and random in-plane orientation of the
nanoplatelets in ensemble. The data analysis allows us to estimate the time and
energy parameters of the bright and dark excitons. The optical alignment effect
enables identification of the exciton and trion contributions to the
photoluminescence spectrum even in the absence of a clear spectral line
resolution.
