Spin - orbit coupling and quasi - nephelauxetic effect in Ce3+

A quasi-nephelauxetic effect has been found in Ce3+ ions in different crystal matrices by employing spin-orbit interaction for the ground level F-2(5/2). The corresponding matrix elements have been determined and normalized relative to the free ion Ce IV- value. These ratios as a function of the crystal field strength N-V exhibit a distinct depression below the free-ion limit. Relationships have been depicted between the number n(P) of crystal-field parameters employed or the maximum splitting of F-2(5/2), on one side, and the crystal field strength, on the other. Examples have been presented with a number of crystals containing Ce3+ ions with different symmetry sites and ligands.