We investigated oxygen defect states in SrTiO3 (STO) thin films by using photoluminescence spectroscopy and spectroscopic ellipsometry. The oxygen-deficient STO homoepitaxial films were fabricated by using different oxygen partial pressures and flow rates for controlling the amount of oxygen vacancies systematically. The visible emission and absorption increased simultaneously with increasing oxygen vacancy concentration in the STO thin films. Given the absolute values of the optical constants, we discussed the origins of the visible absorption features in the STO thin films, in relation to the defect formation and related electronic reconstruction. (C) 2017 Elsevier B.V. All rights reserved.