Changes of force constants near rare-earth impurity sites in CaF2

Abstract

The central force constants associated with the nearest-neighbour fluorine ions and the next-nearest-neighbour calcium ions have been calculated for trivalent rare-earth impurity ions in CaF₂. The results are consistent with force constants used to fit absorption induced in the far-infrared by rare-earth impurities. It is concluded that there is very little variation in the nearest-neighbour central force constant across the lanthanide series.