  The recent proposal of antidoping scheme breaks new ground in conceiving
conversely functional materials and devices, yet the few available examples
belong to the correlated electron systems. Here we demonstrate both
theoretically and experimentally that the main group oxide BaBiO$_3$ is a model
system for antidoping using oxygen vacancies. The first principles calculations
show that the band gap systematically increases due to the strongly enhanced
BiO breathing distortions away from the vacancies and the annihilation of Bi 6s
and O 2p hybridized conduction bands near the vacancies. The spectroscopic
experiments confirm the band gap increasing systematically with electron
doping, with a maximal gap enhancement of 75% when the film's stoichiometry is
reduced to BaBiO$_{2.75}$. The Raman and diffraction experiments show the
suppression of the overall breathing distortion. The study unambiguously
demonstrates the remarkable antidoping effect in a material without strong
electron correlations and underscores the importance of bond disproportionation
in realizing such an effect.
