Low-symmetry Td-distorted Co2+ centres in ceramic ZnO:Co

The reflectivity and photoluminescence of cobalt-doped ZnO ceramics samples have been studied by optical spectroscopy. The result reveals, in addition to the emission bands associated with intrinsic defects, weak narrow emission peaks which are ascribed to a mixed 4T1(P), 2T1(G), 2E(G) → 4A2(F) transition between Co2+ d-levels located in regular Zn2+ sites, [Co2+]Zn and a broad near infrared emission band centred at 710 nm which has been interpreted as belonging to Co2+ ions located in a perturbed Zn2+ site, [ Co 2 + ] Zn ∗ . This study shows that the annealing treatment at 800 °C activates the diffusion of point defects thus creating more [Co2+]Zn centres.