Zeeman-Hyperfine Measurements of a Pseudo-Degenerate Quadruplet in CaF2:Ho3+

We report Zeeman infra-red spectroscopy of electronic-nuclear levels of 5I8 → 5I7 transitions of Ho3+ in the C4v(F–) centre in CaF2 with the magnetic field along the 〈111〉 direction of the crystal. Transitions to the lowest 5I7 state, an isolated electronic doublet, and the next group of states, a pseudo-quadruplet consisting of a doublet and two nearby singlets, exhibit strongly non-linear Zeeman splittings and intensity variations. Simulated spectra based upon a crystal-field analysis give an excellent approximation to the data, illustrating the strong predictive ability of the parametrized crystal-field approach. Anti-crossings in the hyperfine splittings, the basis of quantum information storage in rare-earth doped insulating dielectrics, are also predicted.