Thermal Effects on the Fluorescence Lines of Sm2+ in Crystals

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Abstract
The effects of temperature on the fluorescence lines of Sm2+ in CaF2, SrF2, and BaClF were studied. The results for the first two samples were obtained in the region 10°–100°K. For CaF2 a strong dependence of the linewidth on temperature was found; this width is ∼ 1.7 cm−1 at 15°K and ∼ 40 cm−1 at 95°K. For SrF2, the linewidth is constant and equal to ∼ 2.15 cm−1 up to ∼ 77°K. This difference in behavior is explained qualitatively as due to the fact that in CaF2 the metastable state belongs to the 4f55d configuration and therefore, the electron charge is strongly affected by the thermal perturbations of the environment. We also measured the widths and positions of several fluorescence lines of BaClF:Sm2+ in the 30°–600°K region. The thermal broadening of most of these lines is explained as due to microscopic strains and Raman scattering of phonons, the thermal shifts as due to emission, and absorption of virtual phonons. A Debye model of phonon distribution was used with the same TD for both the lineshift and linewidth.