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 g=3.4l7±0.001 for Yb3+ and g=6.754±0.005 for Er 3+ indicating that a Γ7 doublet is the ground state in both cases. The Er3+ Γ7 ground state shows that a large variation in the B4/B6 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 A(171Yb)=881±1×10-4 cm-1, A( 173Yb)=242.9±0.3×10-4 cm-1, and A(167Er)=233.5±0.3×10-4 cm-1. Axial spectra were also observed but not measured due to their low intensity and linewidth variation with magnetic-field orientation.