Photoluminescence (PL) emission spectroscopy was employed to probe the nature of deep center emissions in GaN. The room temperature PL spectrum measured in the infrared (IR) region revealed an emission band centered around 1.23 eV. Based on detailed analysis of both the IR and visible emission spectra, we suggest that this emission band is a band-to-impurity transition involving a deep level complex consisting of a gallium vacancy and an oxygen atom sitting on one of the neighboring nitrogen sites; the (VGa - O N)2- charge state of (VGa - ON) 2-/1-. Two electronic structures, which arise due to two different configurations of (VGa - ON) 2-/1-, with O N either along the c-axis (axial configuration) or in one of the three equivalent tetrahedral positions (basal configuration), were observed. Our result also provides explicit evidence that both the yellow luminescence band and the 1.23 eV emission line in GaN are related to a common deep center, which is believed to be (VGa - ON)2-/1-.