The authors have obtained the absorption and emission spectra for the Sm 2+ impurity in the mixed fluorides, Ca 1-x Y x F 2+x and Ca 1-x La x F 2+x . From these spectra they conclude that the Sm 2+ ions tend to be coordinated by one or more extra F - ions in addition to the normal eightfold coordination expected in CaF 2 . Measurements of the emission lifetime and intensity as a function of temperature lead them to propose that the luminescence quenching of Sm 2+ in the mixed fluorides is due to a competition between ionisation of the 4f 5 5d level with relaxation into the 5 D 0 (4f 6 ) emitting state. In addition, the thermal activation energy for Sm 2+ emission quenching in various alkaline-earth halides is consistent with the calculated optical separation of the 4f 5 5d level from the conduction band of the host, lending further support to the ionisation mechanism of emission quenching.
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Chase et al. (1987) studied this question.
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