Abstract
The authors have obtained the absorption and emission spectra for the Sm2+ impurity in the mixed fluorides, Ca1-xYxF2+x and Ca1-xLaxF2+x. From these spectra they conclude that the Sm2+ ions tend to be coordinated by one or more extra F- ions in addition to the normal eightfold coordination expected in CaF2. Measurements of the emission lifetime and intensity as a function of temperature lead them to propose that the luminescence quenching of Sm2+ in the mixed fluorides is due to a competition between ionisation of the 4f55d level with relaxation into the 5D0 (4f6) emitting state. In addition, the thermal activation energy for Sm2+ emission quenching in various alkaline-earth halides is consistent with the calculated optical separation of the 4f55d level from the conduction band of the host, lending further support to the ionisation mechanism of emission quenching.