Electron Spin Resonance Spectra of Er3+ and Yb3+ in Single Crystals of SrCl2

The ESR spectra of Yb³⁺ and Er³⁺ in cubic sites of SrCl₂ (Fluorite structure) have been observed at a frequency of 10 Gc/sec and at 4.2° and 20°K. The spectra were isotropic with $\text{g\hspace{0.17em}=\hspace{0.17em}3.417\hspace{0.17em}±\hspace{0.17em}0.001}$ for Yb³⁺ and $\text{g\hspace{0.17em}=\hspace{0.17em}6.754\hspace{0.17em}±\hspace{0.17em}0.005}$ for Er³⁺ indicating that a Γ₇ doublet is the ground state in both cases. The Er³⁺ Γ₇ ground state shows that a large variation in the $B_4{\mathrm{\hspace{0.17em}/\hspace{0.17em}B}}_6$ ratio consistent with the point‐charge model is not present in the more inflated SrCl₂ lattice relative to other fluorite‐type hosts. The Yb³⁺Γ₇ ground state is in agreement with previous measurements on Yb³⁺ in eightfold coordinated cubic sites and no behavior inconsistent with predictions of the point‐charge model was in evidence. Hyperfine structure was resolved with ${\mathrm{A(}}^{171}\mathrm{Yb}{\text{)\hspace{0.17em}=\hspace{0.17em}881\hspace{0.17em}±\hspace{0.17em}1\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}$ , ${\mathrm{A(}}^{173}\mathrm{Yb}{\text{)\hspace{0.17em}=\hspace{0.17em}242.9\hspace{0.17em}±\hspace{0.17em}0.3\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}$ , and ${\mathrm{A(}}^{167}\mathrm{Er}{\text{)\hspace{0.17em}=\hspace{0.17em}233.5\hspace{0.17em}±\hspace{0.17em}0.3\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−4}}{\mathrm{cm}}^{\text{−1}}$ . Axial spectra were also observed but not measured due to their low intensity and linewidth variation with magnetic‐field orientation.