A way of lowering the uncertainty in values of crystal field parameters derived from the spectra of Ln3+ ions in cubic field with rhombic distortions

Potentialities of increasing the reliability of crystal field parameters (CFPs) obtained from an analysis of Stark splitting of J-states of spin–orbital multiplets 2S+1LJ of the Ln3+ ions in cubic crystal field with rhombic distortions via a reduction of the region of their final fitting are examined. Suggested method of lowering the uncertainty of the CFP consists in determination of the relation of general cubic CFP of the fourth and sixth ranks (B4 and B6) by comparison of a fragment of the experimental Ln3+ spectrum with well known picture of dependences of Stark splitting of J-states on the relation mentioned. These dependences were calculated many years ago and published as a set of diagrams by K. Lea, M. Leask, W. Wolf, J. Phys. Chem. Solids, 23 (1962) 1381. Cubic parameters derived from the relation determined can be used for a narrowing of the fitting region for the rest of CFP. The method described is applied to the luminescence spectra of dimeric europium carboxylates with heterocyclic diimines. To justify application of this method to the spectra of Eu3+ ions in crystal field of cubic symmetry with rhombic distortions it was shown that the influence of the second rank components of the crystal field on the relative Stark splitting of J-states of europium ions is minimal for J = 3, 4. In some cases, this peculiarity provides an approach of Stark splitting of the levels with J = 4 in spectra of compounds with rhombic distortions of cubic crystal field to the image of the splitting at an effective field of cubic symmetry. It was demonstrated that for europium complexes under consideration the relation of the general CFP B4/B6 > 119. Consequently, the CFPs of the sixth rank are very small and the region of fitting of the rest of CFP can be appreciably reduced.