Nanostructured TiO2 thin films can be used for many photo-activated processes, such as photovoltaics, photocatalytic water-splitting and waste remediation. However, the performance of TiO2 in solar applications is limited by its wide band gap (∼3 eV), which only allows light absorption in the uv region on the spectrum. Transition metal doping can be used to engineer the band gap of TiO2 to enhance the visible light response. Nanostructured anatase TiO2 thin films co-doped with iron and chromium were synthesized in a single-step gas phase flame aerosol reactor (FLAR). These films are found to absorb visible light. The band gaps of these doped thin films were measured using uv-vis absorption spectroscopy, and compared to those of substitutionally-doped bulk anatase as calculated using self-interaction-corrected density functional theory. The use of a self-interaction corrected exchange-correlation potential significantly alleviated the well-known underestimation of TiO2 band gaps using conventional DFT exchange-correlation functionals.