We report a study of the optical properties of GaN grown on Si(111) by gas source molecular beam epitaxy with ammonia. Temperature dependence of edge luminescence was studied in the range of 77-495 K for samples with low background carrier concentrations, as determined by capacitance voltage profiling and Raman spectroscopy, and the results were fitted using Passler's and Varshni's models. We also demonstrate strong correlation between electron concentration in GaN and relative Raman intensity of A 1 (longitudinal optical) and E 2 2 modes. The binding energy of free excitons is estimated to be 29±2meV. The contributions of different mechanisms to free exciton line broadening are discussed.