Tb 3+ Ion Optical and Magneto-Optical Properties in the Cubic Crystals KTb 3 F 10 .

The optical and magneto-optical characteristics of KTb 3 F 10 crystals in the transition region of 5 D 4 → 7 F 6  4 f 8 configurations of the Tb 3+ ion at temperatures of 90 and 300 K were studied. The schemes of the optical transitions in the KTb 3 F 10 crystals were constructed, and the energies of most of the Stark sublevels of the ground 7 F 6 and excited 5 D 4 multiplets of the Tb 3+ ion split by the C 4v symmetry crystal environment were determined. The presence of three- and two-doublet states in the energy spectra of the Tb 3+ ion multiplets 7 F 6 and 5 D 4 , respectively, was established, which is in good agreement with theoretical predictions. The use of the wavefunctions of the Stark sublevels of multiplets split by a tetragonal crystal field and combining in the studied optical transition made it possible to explain some of the magnetic and magneto-optical features observed in the KTb 3 F 10 single crystals.