The optical absorption of defect centers in SrTiO3 substrates grown by the Vernuil method are investigated using photoinduced electron paramagnetic resonance (photo-EPR) at room temperature. As received samples revealed EPR signatures for Fe3+, Cr3+, Mn4+, and an iron-oxygen vacancy complex, Fe3+VO. An anneal in dry oxygen at 800 °C decreased the intensity of all of the centers except, Mn4+. More significantly, the anneal induced a new charge state of Fe, Fe5+. Photo-EPR data of the annealed samples were interpreted in terms of two defect levels, the 4+ to 5+ transition of Fe (Fe4+/ 5+) at 2.5 eV below the conduction band edge and the 3+ to 4+ transition of the iron-oxygen vacancy complex (Fe3+/ 4+VO) at 1.2 eV above the valence band edge. The former is consistent with reported defect levels and the latter provides a modified value based on measurements over a larger portion of the band gap than had been reported previously. © 2010 American Institute of Physics.