Nature of magnetic circular dichroism and absorption spectra of f-f transitions in Na0.4Ho0.6F2.2 single crystal

https://doi.org/10.1016/j.chemphys.2024.112257

We present first study of magnetic circular dichroism (MCD) spectra of Ho³⁺ ion in C_4v local symmetry, which it has in fluorite Na_0.4Ho_0.6F_2.2. Optical absorption and MCD spectra were studied in this single crystal in the region of ⁵I₈→ ⁵F₃, ⁵F₂, ³K₈ and ⁵G₅ transitions in the temperature range 3.6–––90 K. It was revealed, that number of transitions observed in the MCD and absorption spectra coincides with the number of transitions only from the doublet E state to singlet excited states. The E-E type transitions are not active in MCD, but they are not observed in the absorption spectra either. Paramagnetic magneto-optical activities (MOA) of the absorption bands and their temperature dependences were measured and interpreted with the help of the theory based on the nature of f-f transitions allowance. The MCD spectra were also analyzed in approximation of the �,±�� wave functions of the free atom. It was shown in particular, that the lowest initial state of the transitions observed at T > 10 K had M_J = 7, but this is not the lowest state of the holmium ion in the crystal. A little lower there is a quasi-doublet with M_J = 8 and, accordingly, with a higher magneto-optical activity of transitions from it. However, the intensity of transitions from this state is low.