Results of electron-nuclear double-resonance experiments performed on four shells of fluorine nuclei surrounding ${\mathrm{Yb}}^{3+}$ impurities at cubic sites in the four fluorite lattices ${\mathrm{CdF}}_2$, ${\mathrm{CaF}}_2$, ${\mathrm{SrF}}_2$, and ${\mathrm{BaF}}_2$ are reported. The data are described in terms of a Hamiltonian for the transferred hyperfine interactions (THFI) including an anisotropic nuclear Zeeman term. The contribution of the dipole-dipole magnetic interaction $A_d$ is analyzed for different coordination spheres using calculated values for the impurity-ligand distance. These are obtained from a model for the local distortions around trivalent rare-earth impurities. The covalent contributions to the THFI constants are important for nearest neighbors, and a comparison of the values determined for ${\mathrm{Yb}}^{3+}$ is made with a similar set for the isoelectronic (4$f^{13}$) ${\mathrm{Tm}}^{2+}$ ions in the same lattices.

• Received 28 August 1984

DOI:https://doi.org/10.1103/PhysRevB.32.64