Structural analysis of Fe3+ centers in Tl2MgF4 and Tl2ZnF4 fluorine compounds

• Local structures around Fe3+ impurity forming various centers in Tl2MF4 investigated.
• Suitable structural models for the centers presented by analyzing EPR data.
• Correlation between the experimental data and theoretical values for ZFS provided.
• A clear compression of the MF6 octahedron around tetragonal Fe3+ center shown.
• Both ligand length and angular distortions found for low symmetry centers.

Theoretical analysis of the Fe3+ centers observed in Tl2MgF4 fluorine crystals have been carried out by means of semi-empirical approaches. The most appropriate models are proposed by matching the theoretically predicted zero-field splitting parameters (ZFSPs) with the experimental ones obtained by EPR spectroscopy. Compression on the MF6 octahedron of tetragonal (TE) center I is indicated in both Tl2MgF4 and Tl2ZnF4. A structural model for monoclinic (MO) center II and orthorhombic (OR) Fe3+ center IV in Tl2ZnF4 is proposed by assuming that the substitution of Fe3+ induces both ligand length and angular distortions.