Photoluminescence Investigation of Defects and Optical Band Gap in Multiferroic BiFeO3 Single Crystals

Optical measurements have been carried out on high-quality BiFeO 3 single crystals in order to show the presence of electronic defect states and calculate the band gap. The photoluminescence spectra show an intense electronic transition peak at a wavelength of 410 nm. This peak is large and asymmetric, indicating the existence of defects inside the gap, which we attribute to oxygen vacancies. These defects are likely to originate from the slow heating rate and long sintering times necessary to synthesize BiFeO 3 single crystals. The optical band gap is measured to be 3 eV, a larger value than those previously reported.