Infrared and electron-paramagnetic-resonance spectra of trivalent rare-earth ions in hydrogenated strontium-fluoride crystals

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Abstract
Infrared measurements of hydrogenated strontium-fluoride crystals containing trivalent rare-earth ions, and EPR measurements of hydrogenated strontium-fluoride crystals containing gadolinium are reported. The infrared results show that the hydride ions associated with the rare-earth ions occur in several different sites whose relative occurrence changes abruptly in the vicinity of holmium. For the rare-earth ions before holmium in the rare-earth series, there are two principal sites. One of these has tetragonal symmetry and the other rhombic symmetry. These two sites, and two additional sites of rhombic symmetry, are also observed in the case of the gadolinium-doped crystal by EPR. For the heavier rare-earth ions beyond holmium in the rare-earth series, the tetragonal and rhombic symmetry sites are replaced by a low-symmetry site. Additional sites produced by ultraviolet irradiation of the crystals and the sites observed in the hydrogenated barium-fluoride crystals containing trivalent rare-earth ions are also described. Possible models for the various sites are proposed.