Evidence of Phonon Annihilation Processes in the Excited States of BaClF:Sm2+

We have found direct evidence of upward, phonon annihilation, processes in the decay patterns of two metastable states ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}\left(14\mathrm{}542 {\mathrm{cm}}^{-1\mathrm{}}\right)$ and ${}_{}{}^5{}_{}{}^{}D_1^{}{}_{}{}^{}\left(15\mathrm{}878 {\mathrm{cm}}^{-1\mathrm{}}\right)$ of BaClF: ${\mathrm{Sm}}^{2+}$. Under pulse excitation, the decay curve of the ${}_{}{}^5{}_{}{}^{}D_1^{}{}_{}{}^{}$ fluorescence includes a long tail, with a time constant equal to the lifetime of ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}$, which appears at ∼280°K and grows in intensity with temperature; finally at ∼400°K both states decay with the same time constant. This finding is consistent with the thermal dependence of the ratio of the intensities of the ${}_{}{}^5{}_{}{}^{}D_1^{}{}_{}{}^{}$ to the ${}_{}{}^5{}_{}{}^{}D_0^{}{}_{}{}^{}$ flourescence.