“…The origin of the band situated between 375 and 475 nm is attributed to the electron transition from the donor level formed by oxygen vacancies to the acceptor level formed by other defects and impurities, in our case formed by antimony ions. With increasing the antimony doping level, substitution by antimony ions becomes improved, and due to the oxidation effect, the number of Sb þ 5 ions increases, so the donor level is enhanced [29,30]. Insertion of Sb þ 5 ions in sites with smaller valence states can create oxygen vacancies in the host matrix due to the differences in valence states, in agreement with UV-vis data.…”