HYPERFINE RESONANCES IN THE TETRAGONAL CENTER OF HO3+ IN CAF2

The ground state hyperfine resonances of the C4v centre of Ho3+ in CaF 2 have been detected by using a hole burning microwave-optical double- resonance technique. Resonances are detected, in zero magnetic field, at 2.250, 1.608 and 0.842 GHz corresponding to the transitions between the hyperfine levels of the ground electronic state. In addition, wea ker signals are observed at 2.340, 1.669 and 0.872 GHz. These resonanc es correspond to the hyperfine transitions within the neighbouring ele ctronic state 1.7 cm-1 higher in energy, and result from thermally all owed electronic transitions between hyperfine levels with the same nuc lear spin projection. The low field Zeeman behaviour of these resonanc es has also been studied and updated values for the hyperfine and crys tal field splitting parameters are reported.