A MEAN RADIUS FOR THE FIRST COORDINATION SHELL IN LANTHANIDES

A mean radius R ($) over bar for the first coordination shell of lanth anides in solids is defined in terms of Morrison's local polarizabilit y model, substituting the shifts of the Slater and spin-orbit paramete rs by their observed phenomenological values. The results obtained agr ee within 10% with the measured ion-nearest neighbors' distances in ra re-earth compounds. We used our definition bf a mean radius to predict the average Eu3+-nearest ligand's distance in new luminescent polymer electrolytes. The values found for different concentrations of EU(3+) (2.3-2.7 Angstrom) are compatible with known data for europium.