Complexes of low symmetry involving hydride ions paired with trivalent rare earth ions in calcium fluoride. (IR absorption and EPR)

Abstract

When hydrogen is diffused into calcium fluoride crystals which contain a rare earth impurity and a relatively low concentration of oxygen two types of RE³⁺-H^- complexes of lower than axial symmetry are formed. These centres have been detected by measurements of the infrared absorption from the localization vibrations of the paired H^- (or D^-) ions. In crystals containing Ce³⁺ ions, a new EPR spectrum has been observed which correlates with one of these centres. Models for the centres are discussed, and it is suggested that one may be a simple modification of the trigonal (T₂) centre RE³⁺O^2-F₇^-, where one of the F^- ions is replaced by an H^- ion.