Electron paramagnetic resonance measurements were made of 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+ center with tetragonal symmetry (center I) were observed for both crystals. Signals from an Fe3+ center with monoclinic symmetry (center II) were also observed for Tl2ZnF4. On the basis of the spin-Hamiltonian separation analysis, center II was ascribed to an Fe3+ ion substituting for a Zn2+ ion with a nearest Tl+ vacancy. The center with orthorhombic symmetry (center IV) observed in some Fe, Li co-doped Tl2ZnF4 crystals was attributed to an Fe3+ ion associated with a Li+ ion at the nearest Zn2+ site. Anomalies were found in the fine structure parameters b20 for centers I and the separated parameters b2a(1) for centers II and IV, which had about twice the magnitude of the corresponding values in Rb2ZnF4.

An Electron Paramagnetic Resonance Study of Fe3+ Centres in Tl2MgF4 and Tl2ZnF4 Crystals. M.Arakawa, A.Okamoto, H.Ebisu, H.Takeuchi: Journal of Physics - Condensed Matter, 2006, 18, 3053-67