Investigations of the local structure and the g factors for the tetragonal Er3+ center in KMgF3

The local structure and the electron paramagnetic resonance (EPR) g factors for the tetragonal Er3+ center in KMgF3 are theoretically studied by using the perturbation formulas of the g factors for a 4f11 ion in tetragonal symmetry. In these formulas, the contributions to the g factors from the second-order perturbation terms and the admixtures of various states are taken into account. Based on the studies, the impurity Er3+ is expected to occupy the octahedral Mg2+ site, associated with an oxygen ion substituting for one of the nearest F− (i.e., OF) in the C4 axis, due to charge compensation. Because of the electrostatic attraction of the compensator OF, the Er3+ ion is found to take an axial displacement ΔZ (≈ 0.07 Å) towards the compensator along the C4 axis. The calculated g factors based on the above displacement ΔZ show reasonable agreement with the observed values.