High pressure luminescence studies of localized excitations in ZnS doped with Pb2+ and Mn2+

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Abstract
High pressure luminescence measurements have been made on ZnS doped with Pb+2 and Mn+2. The data include changes in peak energy and shape, integrated intensities, and lifetimes. These localized emissions are treated in terms of a single configuration coordinate model. For Pb+2 the emission peak shifted to lower energy by a moderate amount and narrowed. For excitation in the Pb+2 absorption the intensity was independent of pressure, which is consistent with the fact that the energy barrier for radiationless return to the ground state was high at all pressures. For excitation in the ZnS absorption edge the intensity decreased significantly with pressure above about 80 kbar. Data on shifts of the conduction band with pressure would indicate that one is approaching a transition from a direct to indirect transition at high pressure so that decrease in emission intensity may be associated with decreased absorption efficiency. The Mn+2 emission peak shifted strongly to lower energy with increasing pressure. The direction and magnitude of the shift were consistent with the predictions of ligand field theory. The intensity doubled in 100 kbar, while the lifetime decreased by roughly a factor of 2. These results could be described in terms of a model for a phonon assisted transition. In addition, peak location, intensity, and lifetime measurements were made on ZnS:Pb:Mn. There is clear evidence of energy transfer by exchange, but in addition there is a nonradiative process in the doubly doped crystal which affects both intensities and lifetimes.