Abstract
We have previously reported on the fluorescent efficiency differences with CR excitation between Y2O2S and La2O2S as hosts for RE activators1), and also the effect of mixed lattices (La1-xYx)2O2S on the efficiency of Eu+3, (Eu+3 being nearly equally efficient in both lattices)2). In this paper we examine the behavior, in (La1-xYx)2O2S, of 0.5% Er2O2S. The addition of Y to La2O2S :0.5% Er2O2S causes immediate and continuing decrease in output for CR excitation. We have attempted to determine the cause of this decrease by measuring the effectiveness of photon excitation as a function of Y content. Lattice absorption (band gap) displays qualitatively the same efficiency losses as for CR. With various 4f absorptions we find that Er has indeed been incorporated in all of the mixed crystal samples and, within the experimental error, operates at the same quantum efficiency. We can deduce then, that the low efficiency of the Y-containing lattices arises from the lack of an efficient energy transfer process in surrounds containing Y. The details of the mechanism which allows La2O2S to transfer energy efficiently are still being sought.
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