  Knowledge of the electronic band structure of multiferroic oxides, crucial
for the understanding and tuning of photo-induced effects, remains very limited
even in the model and thoroughly studied BiFeO3. Here, we investigate the
electronic band structure of BiFeO3 using Raman scattering with twelve
different excitation wavelengths ranging from the blue to the near infrared. We
show that resonant Raman signatures can be assigned to direct and indirect
electronic transitions, as well as in-gap electronic levels, most likely
associated to oxygen vacancies. Their temperature evolution establishes that
the remarkable and intriguing variation of the optical band-gap can be related
to the shrinking of an indirect electronic band-gap, while the energies for
direct electronic transitions remains nearly temperature independent.
