An electron paramagnetic resonance study of Fe3+ centres in Tl2MgF4 and Tl2ZnF4 crystals

EPR measurements have been made on as-grown single crystals of Tl2MgF4 and Tl2ZnF4 doped only with Fe and co-doped with Fe and Li using an X-band spectrometer. Signals from the charge-uncompensated Fe3+ centre with tetragonal symmetry (centre I) were observed for both crystals. Signals from an Fe3+ centre with monoclinic symmetry (centre II) were also observed for Tl2ZnF4. On the basis of the spin-Hamiltonian separation analysis, centre II is ascribed to an Fe3+ ion substituting for a Zn2+ ion with a nearest Tl+ vacancy. The centre with orthorhombic symmetry (centre IV) observed in some Fe, Li co-doped Tl2ZnF4 crystals is ascribed to an Fe3+ ion associated with a Li+ ion at the nearest Zn2+ site. Anomalies were found in the fine structure parameters b20 for centres I and the separated parameters b2a(1) for centres II and IV, which have about double the magnitude of the corresponding values in Rb2ZnF4