PHOTOLUMINESCENCE IN ZN1-XCOXSE UNDER HYDROSTATIC-PRESSURE

We report on low temperature measurements of the pressure dependence o f the photoluminescence (PL) associated with Co2+ in ZnSe performed in a diamond anvil cell. Two sharp emission peaks at similar to 2.36 eV, labeled L and L', show a weak redshift under pressure with rapidly de creasing peak intensities. These results, together with the excitation energy and temperature dependence of the PL at 1 bar, allow for a cri tical examination of previous models proposed for these optical transi tions. The PL data are discussed within the framework of conventional crystal-field theory based on the Racah and crystal-field parameters B , C, and Delta(=10Dq). From this analysis, the normalized energy E/B i s determined as a function of the normalized crystal field parameter D q/B. Thus quantitative estimates for the enhancement in the p-d hybrid ization with pressure (evident in the line-shape profiles of the spect ra) are deduced. The energy separation between L and L' decreases cont inuously for modest pressures (similar to 1 GPa), and raises questions about the role of spin-orbit coupling in accounting for the splitting of this emission doublet.