Hyperfine splittings of infrared lines of the cubic centre in CaF₂:Ho³⁺

Hyperfine structure is observed on three transitions of the ⁵I₈ → ⁵I₇ absorption spectrum of the cubic-symmetry centre in CaF₂:Ho³⁺. Hyperfine mixing between the two lowest levels of the ⁵I₈ ground multiplet produces a complex and rich spectrum, which is only partially resolved. Simulated spectra are generated using one parameter to determine electronic crystal-field wavefunctions and one for the crystal-field splitting of the near-degenerate ground state. The simulated spectra correspond well with the measured spectra and demonstrate that the complex structure is well accounted for by dipole-hyperfine mixing between the lowest triplet and doublet states in the ⁵I₈ ground multiplet.