Ligand ENDOR in alkaline earth fluorides containing Gd3+at cubic sites

Abstract
It is found that small terms of the form S3I are needed in the spin Hamiltonian to give a correct account of the ligand ENDOR for Gd3+ in CdF2, CaF2 and SrF2. Comparison of the ligand hyperfine parameters for Gd3+ in these materials and for BaF2 suggests that there may be a significant contribution from electrostatic polarization of the ligands.