An electron paramagnetic resonance study was made of single crystals of material which had been doped with Gd3+ and Na+. A new weak spectrum with monoclinic symmetry was detected. It was found that the principal z-axis deviated by about 8 in the case of CsCdF3, and by 6 in the case of CsCaF3, from the crystalline axis; in a <100> direction. The new center was attributed to a Gd3+ ion that was associated with a Na+ ion at the nearest divalent cation site. Its intervening F- ion was thought to be displaced from the face-center point and towards a <110> direction normal to the Gd3+-Na+ pair axis. The out-of-axis displacement showed that the intervening F- ion on the pair axis became unstable because of the existence of the associated Na+ ion.

M.Arakawa, H.Ebisu, H.Takeuchi: Journal of the Physical Society of Japan, 1995, 64[4], 1356-62