Analysis of f–d excitation spectra of heavy lanthanide ions in various crystals based on the simple model for f–d transition and its correction caused by the 5d spin–orbit interaction

The simple model for f–d transitions of heavy lanthanide ions in crystals has been extended to more general cases applicable to the octahedral six-fold coordination compounds where the measured spectra involve the low-lying 2t2 component of 5d orbitals, for which the 5d spin–orbit splitting is considerable and can be as large as a few thousand wavenumbers for heavy lanthanide ions. A quasi-angular-momentum technique was employed to deal with the correction caused by the 5d spin–orbit interaction based on the equivalence between the t2 and p orbits. The extended and original models were successfully applied to the interpretations of the f–d excitation spectra of Tm3+ ions in Cs2NaYF6 and CaF2 crystals. The impact of the 5d spin–orbit interaction on the f–d transition spectra was also discussed in more details.