Luminescence polarization of CdSe microcrystals

We have considered theoretically the polarization of the luminescence of small CdSe microcrystals due to the hexagonal structure of the lattice. We derive the energy spectrum and wave functions of holes in spherical microcrystals. It is shown that the value of the splitting between the A and B hole states in microcrystals could be five times smaller than the corresponding value of crystal-field splitting in bulk hexagonal semiconductors. The times of radiative recombination and the polarization of light connected with transitions between the electron and hole quantum size levels (QSL's) were calculated. The time dependence of the luminescence polarization has been found. At the first instant after short impulse excitation the degree of polarization should be equal to 13/51. It is shown that nonequilibrium electron-hole pairs, with long lifetimes, are formed in microcrystals as a result of the hole thermalization to the A state after excitation into the B state. The recombination of these states requires the participation of phonons, resulting in a strong dependence of the recombination rate on the temperature. The degree of luminescence polarization of these states depends on the type of phonons involved in optical transitions.