Thermal Dependence of Fluorescence and Lifetimes of Sm2+ in Several Host Lattices

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Abstract
Fluorescence spectra and lifetimes of Sm2+ in CaF2 and SrF2 were studied from 15° to 300°K and in BaClF from 15° to 650°K. A sharp line appears above a wide background at ∼100°K and 14 115 cm−1 for CaF2:Sm2+ and at 140°K and 14 350 cm−1 for SrF2:Sm2+. Lifetimes at 80°K are ∼2×10−6 and ∼10−3 secs, respectively, in agreement with previous workers' results. BaClF:Sm2+ presents several sharp lines corresponding to transitions from three metastable states 5D0 (14 542 cm−1), 5D1 (15 878 cm−1), and 5D2 (17 820 cm−1) to the ground‐state multiplets 7F0 to 7F4. The most efficient states at 300°, 80°, and 15°K are, respectively, 5D0, 5D1, and 5D2; above 350°K, the 5D1 fluorescence increases relatively to the 5D0 fluorescence, contrary to what happens from 77° to 350°K. Several 5D0 lines persist and remain sharp (∼4 Å at 650°K) even at high temperatures with no observable background. Under pulsed excitation the decays of the fluorescence lines are consistent with an optical excitation in the 4f55d bands, which is transferred non‐radiatively to the 5D2 state and then cascades to lower levels with rates slower with decreasing temperature and for the 5D1—5D0 energy gap. At 300°K the 5D1 fluorescence presents a double decay, but at higher temperatures the 5D1 decay is purely exponential with the same time constant of 5D0. The continuous and pulsed fluorescence data furnish evidence of pumping by phonon annihilation in the 5D1 state from the lower 5D0 state at temperatures greater than 300°K.