Morphology of the f ⇆ f intensity parameters

The structure of the intensity parameters understood within the framework of ab initio calculations is discussed. The model of f <--> f transitions is extended by completely new third-order effective operators that represent the direct perturbing influence of the specific mass shift effect. The importance of this new mechanism is established in relation to the values of second-order standard Judd-Ofelt terms. The hierarchy of important contributions to the transition amplitude is analysed in the light of the tremendous impact caused by electron correlation effects. The approach is illustrated by the results of numerical calculations performed for the Pr3+; Eu3+ and Sm3+ ions. Special attention is directed to the radial integrals of various effective operators that are evaluated for the complete radial basis sets of one-electron functions.