ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si(100) substrates at a substrate temperature of 550 °C with various oxygen pressures and post-annealing temperatures. The structural characterization was carried out on a series of ZnGa₂O₄ films grown at an oxygen pressure range of 50–300 mTorr, and subsequently post-annealed at 600 and 700 °C. The optimum oxygen pressure for luminescent characteristics was about 100 mTorr. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. A post-annealing treatment of ZnGa₂O₄ thin films led to the different shape of luminescent intensity and grain size. β-Ga₂O₃ phase appeared at an annealing temperature of 600 °C and increased with increasing annealing temperature. We have also investigated the effect of the ligand field strength on the resultant energy levels for ZnGa₂O₄ thin film phosphor. The annealing process at different temperatures may lead to different dominant emissions.