Mossbauer studies are carried out for divalent europium as dopant in the fluorites CaF,, SrF,, and BaF,. The lslEu Mossbauer isomer shift in these materials increases, increases and decreases, respectively, as the Eu2+ concentration decreases below a few mole percent. Previous explanations of these effects as due to lattice pressure or host covalency are found t o be wrong. Instead these trends are interpreted as primarily due to variations in the admixture of t,he prevalent defect structure of E U~+ O : -F~-~~ (i = 1, 2 , 3 , or 4) which stabilizes the Eu2+ in these crystals. Mossbauerstudien werden fur zweiwertiges Europium als Dotierung in den Fluoriten

The Mossbauer electric quadfupole interaction for DyS+ in both oxygen-free and oxygen-injected CaF, is measured between 90 and 630 K. Comparison of the experimental data with theoretical calculations confirms that in oxygen-free CaF2 the stabilization occurs via an interstitial F-ion, while oxygen injection leads t o stabilization by oxygen substitutionally replacing F-ions.Es wird die elektrische MoBbauer-Quadrupolwechselwirkung fiir DY+ in Sauerstoff -freiem und Sauerstoff-dotiertem CaF2 im Temperaturbereich 90 bis 630 K gemessen. Ein Vergleich der experimentellen Daten mit theoretischen Berechnungen zeigt, daB im Sauerstoff-freien CaF, die Stabilisierung durch ein Zwischengitter-F--Ion stattfindet, wiihrend Sauerstoffdotiefung zu Stabilisierung durch Ersetzen von F--1onen durch Sauerstoffionen fiihrt.