EPR studies ofGd3+—metal-ion complexes in SrCl2

EPR experiments of ${\mathrm{Gd}}^{3+}$-$M^{+}$ and ${\mathrm{Gd}}^{3+}$-$M^{2+}$ complexes ($M$ is a metal) in Sr${\mathrm{Cl}}_2$ crystals are reported. The effect of the excess negative charge of the $M^{+}$ impurity on the crystal field is studied and it was found that the second-degree crystal-field parameters can be explained reasonably well on the basis of the point-ion-lattice approximation when one is dealing with small alkali ions. When, however, larger monovalent cations are considered one finds serious discrepancies with the crude point-ion-lattice model.