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 = 3.417 ± 0.001 for Yb3+ and g = 6.754 ± 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 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 × 10−4cm−1, A(173Yb) = 242.9 ± 0.3 × 10−4cm−1, and A(167Er) = 233.5 ± 0.3 × 10−4cm−1. Axial spectra were also observed but not measured due to their low intensity and linewidth variation with magnetic-field orientation.