H and F Bands in Alkaline-Earth Fluorides

Spectral positions of the F-band peaks induced in CaF2, SrF2, and BaF2 by irradiating at LHe temperatures with 50-kV x rays were determined to be at 377, 442, and 611 nm, respectively, and fit an Ivey–Mollwo relation having an exponent of 4. The absorption spectrum of each of the three alkaline-earth fluorides consists of the F band and a band at a shorter wavelength. Both appear to be composite bands. A simultaneous decrease of both bands was obtained by dark bleaching and also by illuminating with F-band light. It is suggested that the bands at shorter wavelength are analogous to the near-uv bands seen in x-ray-irradiated alkali halides. Spectral positions of the peaks assigned to be due primarily to H centers are at 314, 325, and 364 nm in CaF2, SrF2, and BaF2, respectively, and fit an Ivey–Mollwo relation with the exponent 1.5.