Hyperfine interactions in YAB:Ho3+: A high-resolution spectroscopy investigation

High-resolution spectroscopy (as fine as 0.01 cm−1) was applied to a 1 mol % holmium-doped single crystal of yttrium aluminum tetraborate with the purpose of studying the hyperfine splitting of Ho3+ energy levels of interest for possible quantum manipulation media. The hyperfine structure was clearly revealed for a high number of lines in a wide wave number range (up to 21300 cm−1) and for a large number of multiplets. Several different hyperfine patterns were monitored, differing in the number of lines, in their separation, and in their relative statistical weight. These features were all understood by a crystal-field model, whose results are in very good agreement with experiments and account for the involved level symmetry, the type of transitions (electric and magnetic dipole allowed), the possibility of a second-order (pseudoquadrupolar) hyperfine coupling between close levels, and a slight distortion of the local D3 symmetry in Ho-occupied sites.