Spectra of Hydrogenated Calcium Fluoride Containing Rare-Earth Ions

Hydrogenation of calcium fluoride containing rare-earth impurities results in the settlement of H^- ions in various lattice positions. The electronic spectra of the rare-earth (RE) impurity ions, infrared absorption due to localized vibration of the H^- ions, vibronic spectra of RE³⁺ + H^- ion pairs, and the electron-spin-resonance (ESR) spectra of these pairs are mutually consistent in yielding the position and symmetry of the H^- sites in the lattice. The location of the H^- ions depends on the thermal treatment during and after the hydrogenation. This is observed by reversible and irreversible changes in the various spectra. Spectral changes due to isotopic substitution of H^- by D^- are described and analyzed.