PHOTOLUMINESCENCE POLARIZATION OF SEMICONDUCTOR NANOCRYSTALS

We review the polarization properties of photoluminescence (PL) in nan ocrystals (NCs) from both theoretical and experimental points of view. We show that, under linearly polarized excitation, NCs emit partly po larized light owing to their uniaxial structure or their anisotropic s hape. In elongated NCs, the anisotropy may have two origins, the elect ronic confinement or the effect of depolarizing field created by the l ight-induced charges on the interfaces. Results of polarization studie s in porous silicon are presented. They are explained by the shape of the Si NCs. Experiments in CdSe NCs reveal the fine structure of the e xcitonic levels and show evidence of the enhancement of the electron-h ole exchange energy with decreasing NC size. Spin orientation in wurtz ite-type NCs is achieved by optical pumping with circularly polarized light. The effect of a magnetic field on the degree of circular polari zation and the mechanisms of spin relaxation are discussed. Results in large-size NCs are presented.