A semi-empirical analysis of ZFS parameters for transition metal (TM) ions (Cr3+ and Mn2+) centers in K2MgF4

•Local structures around Cr3+ and Mn2+ impurities in K2MgF4 investigated.•Structural models for centers presented by analyzing EPR data for each center.•The most appropriate structural model for each center proposed.•Tetragonality of MgF6 increases with both Cr3+ and Mn2+ for Mg2+ ion site shown.

The local structure around the transition metal (TM) ions (Cr3+ and Mn2+) centers in K2MgF4, namely tetragonal (TE) center I, monoclinic (MO) center II and orthorhombic (OR) centers III, have been explored by semi-empirical calculations in the frame of superposition model (SPM). We proposed the most appropriate structural model for each center by matching the theoretically predicted zero-field splitting parameters (ZFSPs) with the experimental ones obtained by EPR spectroscopy. It is shown that the tetragonality of MgF6 octahedra increases with the substitution of both Cr3+ and Mn2+ for Mg2+ sites as well as with a rather higher value for the latter one. A tilt angle of 12.51° is found for MO Cr3+ center, which is comparatively small, as compared to the other A2BF4 crystals such as K2ZnF4 and Tl2ZnF4. Almost three times larger relaxation of intervening F-ligand than that of other equatorial F-ligands is also indicated for OR Cr3+ center.