The structure of the self-trapped hole in KMgF ₃

Optical and electron spin resonance studies have been made of the self-trapped holes produced by irradiation of KMgF 3 at 77°K. These are found to have the F 2 - molecular ion structure. Because of the low symmetry of anion pairs in the perovskite lattice, none of the principal axes of the tensors describing the hyperfine interaction with each of the two nuclei lie along the molecular axis. Thus the molecular ion has a `bent bond' configuration similar to that found for V F centres in LiF. The inclination of the axes of the ground state orbitals to the molecular axis is found to be 7°.