Local structural properties of (NiF6)4− clusters in perovskite fluorides RbMF3 (M = Cd2+, Ca2+, Mg2+) series: EPR and optical spectra study in tetragonal and trigonal ligand field

By analyzing EPR and optical spectra, the local lattice structures of (NiF6)4− clusters in perovskite fluorides RbMF3 (M = Cd2+, Ca2+, Mg2+) series in tetragonal and trigonal ligand field are studied. A compression distortion relative to the regular octahedron for the RbCdF3:Ni2+ and RbCaF3:Ni2+ systems is determined. Furthermore, on the basis of the complete energy matrices we found that ZFS parameter D dependence on spin–orbit coupling coefficient ζ is not a strictly quadratic relation as shown by the fourth-order perturbation formula. Finally, the curves of g∥ versus k and g⊥ versus k for these three systems are plotted which satisfy an approximately linear relation.