An EPR study of trigonally symmetric Cr3+ centres in TlZnF3 single crystals

EPR measurements have been made on the single crystals of TlZnF3 doped with chromium and co-doped with chromium and lithium. For the Cr-only doped crystal, three kinds of Cr3+ spectra with trigonal symmetry were observed. These centres are ascribed respectively to a charge-uncompensated Cr3+ ion at the Zn2F9 unit (Zn site II), a Cr3+ ion associated with a nearest Zn2+ vacancy at the Zn2F9 unit, and a charge-uncompensated Cr3+ ion at the ZnF6 unit (Zn site I). In the Cr, Li co-doped crystal, preferential formation of a Cr3+-Li+ pair at the Zn2F9 unit was found. The ligand octahedra are considered to be elongated in the Cr3+-Zn2+ and the Cr3+-Li+ centres at the Zn2F9 units and compressed in the Cr3+ centre at the ZnF6 unit.