THEORETICAL INTENSITIES OF 4F-4F TRANSITIONS BETWEEN STARK LEVELS OF THE EU3+ ION IN CRYSTALS

We report a theoretical calculation of the intensities of the 4f-4f transitions between Stark levels of the Eu3+ ion in KY3F10, LiYF4 and LaOCl hosts. A ligand field Hamiltonian, described by a simple overlap model, is initially applied to oxychlorides, oxybromides and fluorides doped with the Eu3+ ion. Since for the even rank ligand field parameters, there is a significant improvement with respect to the crude electrostatic approximation, this model is also used in the evaluation of the odd rank parameters required in the intensity calculations. The average energy denominator method used by Bebb and Gold to treat multi-photon ionization processes in hydrogen and rare gas atoms is used here as an alternative procedure to evaluate the electric dipole matrix elements. The results are in good agreement with those given by the standard Judd-Ofelt theory. Only the forced electric dipole mechanism up to second order and the dynamic coupling are taken into account. Emphasis is given to the fact that these two mechanisms should contribute with the same sign to the B-lambda-tp intensity parameters, in contrast with theoretical calculations currently found in the literature. Comparison with experimental values points to the neglect of higher order corrections to these two mechanisms, and the use of a still incomplete representation of the ligand field as the reason for the discrepancies between theory and experiment.