Transfer of energy between three different ions has been observed in CaF2 doped with Yb and Nd. In CaF2, Nd occurs in only the trivalent state, while Yb forms both divalent and trivalent luminescent centers. Evidence for both Yb2+→Nd3+ and Nd3+→Yb3+ energy transfer is presented. Measurement and analysis of Yb2+ fluorescence decay times in crystals containing 0.1 mole % Yb and 1.0 mole % Nd, gave a figure of 0.62 for nonradiative transfer efficiency at 77°K. Sensitization of Yb3+ by Nd3+ produces strong ir emission, principally at 0.9752μ. An approximate estimate of sensitized increase of Yb3+ emission achieved approaches two orders of magnitude.
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Ewanizky et al. (1968) studied this question.
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