Mechanism of the Green-Copper Luminescence in ZnS Crystals. II. Polarization Characteristics

Abstract

The polarization characteristics of the green-copper luminescence were investigated at liquid helium temperature using a melt-grown ZnS:Cu, Al crystal with cubic structure involving stacking faults. In accord with the results of the previous study at liquid nitrogen temperature, the luminescence is polarized preferentially perpendicular to the [111]_c axis. The origin of this polarization is attributed to the crystal field with trigonal nature of the host lattice, and the polarization characteristics are interpreted on the basis of the donor-acceptor pair emission mechanism. With increasing temperature from liquid helium temperature, I_⊥ decreases while I_|| increases keeping I=I_⊥+I_|| constant, I_⊥ and I_|| being the intensities of luminescence polarized perpendicular and parallel to the [111]_c axis. These facts are accounted for, if one takes the thermal excitation of holes associated with copper acceptors into account.