The authors present a detailed theoretical study of the optical behavior of native defects in zinc gallium oxide based on configuration coordinate diagrams derived from hybrid functional calculations. The resulting predicted luminescence lines are compared with low-temperature photoluminescence spectra measured on zinc gallium oxide single crystals grown from the melt. Based on this comparison, self-trapped holes, Zn antisites, Zn vacancies, and their complexes with Ga antisites are put forward as potential origins of the observed luminescence.