Theoretical Investigations of the Local Structure and the EPR Parameters of Mn4+ in LiF:U:Mn Crystal

Abstract

The local structure and the EPR parameters (zero-field splitting D, g factors g‖ and g⊥ and hyperfine structure constants A‖ and A⊥) ofMn4+ in LiF:U:Mn crystal have theoretically been investigated by using the perturbation formulas of the EPR parameters for a 3d3 ion in trigonally distorted octahedra. In this trigonal Mn4+ center, three U6+ ions locate on (1,1,0), (1,0,1) and (0,1,1) sites, each surrounded by six O2− ions. Thus, the studied system is characterized as the Mn4+ associated with one host F− triangle, one O2− triangle and an additional equivalent F’− triangle containing the three U6+ ions, i.e. an [MnF3O3F’3]8− cluster. The central Mn4+ impurity is found to shift towards the oxygen triangle along the C3 (or [111]) axis by an amount ΔZ (≈ 0.29 Å) due to the strong electrostatic attraction between the Mn4+ and the oxygen triangle (and also the additional equivalent F’− triangle), which increases the trigonal distortion of the Mn4+ center considerably. The calculated EPR parameters based on the above displacement ΔZ agree reasonably with the observed values.