Hyperfine patterns of infrared absorption lines of Ho3+C4v centres in CaF2

Hyperfine structure is observed on several infrared transitions to the I-5(7) and I-5(6) multiplets of the Ho3+ C-4v centre in CaF2. Particularly complex and detailed hyperfine structures are observed for transitions to the Y-3 level of the I-5(7) multiplet, which include the appearance of DeltaI(z) not equal 0 transitions. The hyperfine lines of this level are satisfactorily accounted for by strong mixing of close-lying levels of this multiplet by the perpendicular hyperfine interaction, which leads to relaxation of the DeltaI(z) = 0 selection rule and a redistribution of the hyperfine intensities over many transitions. An excellent correspondence is found between the measured and simulated spectra.