A Spectroscopic Study of the Cathodo-Luminescence of Fluorite

Spectra of the cathodo-luminescence of five samples of fluorite.—In the case of natural fluorite, the spectra excited consist of broad diffuse bands upon which are superimposed sharp bands. The effect of heating to 600°C before bombardment is to intensify the sharp bands and to weaken the diffuse ones. The effect of fusion in an oxidizing flame is much more radical, the color is changed and many new narrow bands are emitted. The wave-lengths as determined photographically and visually are given in tables. Comparison with the results of Urbain for cathodo-luminescence spectra of small percentages of rare earths in CaO and in Ca${\mathrm{F}}_2$ shows that the bands observed are due to rare earth impurities the most prevalent and conspicuous being samarium, dysprosium, europium, gadolinium and terbium. The fusion changes the fluoride to the oxide, at least on the surface. The sharpness of the bands and the dependence of the spectra upon the diluent materials is explained if we assume that the rare earth atoms enter into the crystal lattice and emit light under constraint by the neighboring atoms.