Relativistic effects in lanthanides and actinides

The Judd-Ofelt theory of f<---->f transitions was originally developed as a non-relativistic theory nearly 40 years ago. Modifications to include the effects of spin-orbit effects have been developed by various researchers. The inclusion of relativistic effects both for the Judd-Ofelt theory of intensities and for crystal field effects has been hindered, until recent times, by the lack of adequate relativistic radial integrals. It is now possible to obtain reliable relativistic integrals and we show how both the Judd-Ofelt theory and crystal field theory may be modified to accommodate relativistic effects. These extensions involve new effective operators. We include some historical remarks on the development of the Judd-Ofelt theory. (C) 2002 Published by Elsevier Science B.V.