7F6(Γ1g) → (Γ1g)5D4 Two-Photon Transition of Tb3+ in Cs2NaTbCl6

M. Chua and P.A. Tanner Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Hong Kong

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Two-photon spectroscopy has expanded the scope of studies of excited states of ions and has also enabled the examination of the validity of conventional theories. In this study, the direct theoretical calculation of the two-photon intraconfigurational crystal field transitions of 7F6(Γ1g) → 5D4 of Tb3+ in Cs2NaTbCl6 has been performed, based on third-order perturbation theory including electric dipoles and spin-orbit coupling. The core 4f7 (8S7/2 Γ6, Γ7, Γ8) and 4f7(6P7/2 Γ6, Γ7, Γ8) states coupled with 5d(Γ3, Γ5) are taken as the intermediate states. The calculated transition intensity ratios are in good agreement with the experimental results. In particular the two-photon transition 7F6(Γ1g) → ( Γ1g)5D4 is allowed in third-order perturbation instead of the proposed fourth-order process by Ceulemans et al. using the Judd-Pooler-Downer model. The inconsistency between the two studies arises from the failure of application of the Judd-Ofelt closure approximation. The closure approximation does not only simplify the two-photon calculation but also sacrifices the physical accuracy by changing the selection rule of the two-photon transition from that of two electric dipole transitions to that of one electric quadrupole transition.

DOI: 10.12693/APhysPolA.90.169 PACS numbers: 33.80.Wz, 33.20.Kf, 33.70.Fd