Zeeman-Hyperfine Measurements of a Pseudo-Degenerate Quadruplet in CaF 2 :Ho 3+

We report Zeeman infra-red spectroscopy of electronic-nuclear levels of 5 I 8 → 5 I 7 transitions of Ho 3+ in the C 4 v (F – ) centre in CaF 2 with the magnetic field along the 〈111〉 direction of the crystal. Transitions to the lowest 5 I 7 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.