UV-Lumineszenz und seltenerdgehalte in flussspaten

Abstract

Samples of fluorite of various origins and widely distributed throughout the world have been analysed spectrochemically for the rare-earths and other trace elements in order to verify the correlations between their contents of these elements and their fluorescence in U.V. radiation. Statistical evaluation of the results qualitatively confirms the conclusions of earlier investigations that bivalent europium (Eu 2+) is an activator for the blue-violet fluorescence observed at ordinary temperatures, and bivalent ytterbium (Yb 2+) for the yellow-green fluorescence observed at low temperatures. Quantitatively, the earlier results stand in need of correction: the maximum europium content observed, in fluorite from Weardale, England, amounts only to 70 ppm Eu, and the maximum ytterbium content, in fluorite from Erongo, Africa, to 160 ppm Yb. The low-temperature fluorescence requires a threshold content of about 0·1 ppm Yb, and the blue-violet fluorescence a Eu: Yb ratio of 6 with a minimum content of 0·1 ppm Eu. The yellow-green low-temperature fluorescence disappears at a Eu: Yb ratio of about unity. The bivalent rare-earth elements are not incorporated selectively into the fluorite structure, but their concentrations are always related to the overall rare-earth content, the Eu concentration depending upon the content of ceria-earths, and Yb upon the content of yttria-earths. In spite of this, europium may be more strongly concentrated than would be expected from the Oddo-Harkins rule.