Theoretical analysis of the two-photon absorption spectrum of Tb3+ in Cs2NaTbCl6

Abstract

Eighteen selected two-photon absorption (TPA) transitionline strengths with polarization angles θ = 0° and45°,spanning several orders of magnitude, have been calculated for the Tb3+ ion in the cubic hostCs2NaTbCl6.The results are in reasonable agreement with experimental resultsin the literature. The calculation utilized the crystal field (CF)wavefunctions for the initial and final states of the 4f8configuration, and utilized free ion or CF wavefunctions (with the corresponding energies) for4f7core states of the whole intermediate 4f7 5dconfiguration comprising 34 320 states. The intensities of certain transitions werefound to be very sensitive to the inclusion of the CF interaction within the 4f7core. In contrast to previous fourth- or third-order calculations of the TPAtransition line strength of the strong transition (7F6)A1g → (5D4)A1gusing pure Russell–Saunders (RS) wavefunctions for the |7F6 ⟩initial and ⟨5D4 |final states, our second-order direct calculation shows that theadmixed RS wavefunctions |[7F6 ]⟩ and ⟨[5D4 ]|must be used to account for its high intensity. The effects of CF interactions within the 4f7 core,i.e. J-mixingand CF energy level splitting, upon the (7F6)A1g → (5D4)EgTPA transition line strength have been separated, and the latter effect is shown tobe more important for the transition investigated.