Optical polarization of localized hole spins in p-doped quantum wells
  The initialization of spin polarization in localized hole states is investigated using time-resolved Kerr rotation. We find that the sign of the polarization depends on the magnetic field, and the power and the wavelength of the circularly polarized pump pulse. An analysis of the spin dynamics and the spin-initialization process shows that two mechanisms are responsible for spin polarization with opposite sign: The difference of the g factor between the localized holes and the trions, as well as the capturing process of dark excitons by the localized hole states. 
M. Studer, M. Hirmer, D. Schuh, W. Wegscheider, K. Ensslin, and G.   Salis
cond-mat.mes-hall