Endor of 171Yb3+ and 173Yb3+ on cubic sites in calcium fluoride

The energy level scheme for 4f13 in a cubic crystal field is relatively simple. The effect of a perturbation Hamiltonian containing electron and nuclear Zeeman terms and magnetic dipole and electric quadrupole hyperfine interactions can therefore be calculated easily, especially as the experimental results only justify calculation to second order. The second-order effects give several small unusual terms in the spin-Hamiltonian for the ground doublet Γ7. The high precision of endor experiments on171Yb and 173Yb make it possible to measure these small terms and confirm that their magnitude is consistent with the second-order calculation. From the size of the second-order terms we also obtain a value for the energy of the Γ8 state of the lowest J = 7/2 manifold (604 ± 10 cm-1), and a value for the electric quadrupole interaction in the free ion. We have also attempted to measure a hyperfine structure anomaly in order to estimate the contribution of core polarization to the hyperfine interaction, but such an anomaly is too small to be detectable with the precision of measurement we were able to achieve.