Energy levels and photoluminescence properties of nickel-doped bismuth ferrite

Ni-doped BiFeO₃ (BFO) films have been prepared using sol-gel method. Photoluminescence and optical absorption measurements were carried out for the grown films and observed four emissions at 451 nm, 468 nm, 513 nm and 689 nm. The band gap of the Ni-doped BFO was calculated from the absorption data to be 2.75 eV. The spectroscopic data were analyzed in conjunction with the results of conductivity vs. temperature measurements, which showed three different kinds of activation energies related to the defect and dopant levels inside the band gap. The observed emissions were attributed to the transitions from the oxygen vacancy, Bi²⁺ and Ni³⁺ levels, as well as the intrinsic band-to-band transition.