Two up-conversion processes, described by ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$+${\mathrm{}}^1$${\mathrm{D}}_2$→${\mathrm{}}^3$${\mathrm{P}}_0$${+\mathrm{}}^1$${\mathrm{G}}_4$ and ${}_{}{}^1{}_{}{}^{}\mathrm{D}_2^{}{}_{}{}^{}$${+\mathrm{}}^1$${\mathrm{D}}_2$+${\mathrm{}}^1$${\mathrm{D}}_2$→ ${\mathrm{}}^1$${\mathrm{S}}_0$ +${}^3$$H_4$+${}^3$$H_4$, are observed in ${\mathrm{CaF}}_2$:${\mathrm{Pr}}^{3+}$. The analysis of the excitation and fluorescence spectra of the emissions following these processes allows the selective observation of various impurity groups. Ten different impurity sites were detected. The temporal evolution of the up-converted emission arising from these sites provides qualitative information on the interionic coupling strength. In addition to the observation of strongly coupled clusters, the first evidence of intercluster interaction is reported.

• Received 9 August 1985

DOI:https://doi.org/10.1103/PhysRevB.33.4493