Photoluminescence (PL) spectroscopy has been used to investigate the effect annealing has on molecular beam epitaxially grown GaN in different ambients. By observing the changes in the PL spectra as a function of ambient temperature and atmosphere used, important information concerning the origin of defects within GaN has been found. Samples were annealed in different atmospheres, (including oxygen, oxygen and water vapour, nitrogen and argon), different temperatures. In the 2.0eV-2.8eV region of the PL spectra, two peaks appeared at approximately 2.3eV and 2.6eV, somewhat higher than the usual yellow luminescence peak. We find that the 2.6eV peak is dominant for high annealing temperatures and the 2.3eV peak dominates at low annealing temperatures for the samples annealed in oxygen. When annealed in argon and nitrogen the 2.6eV peak dominates at all annealing temperatures. Changes in the PL spectra between anneals were also seen in the 3.42eV region. The 3.42eV peak is often assigned to excitons bound to stacking faults. Power resolved measurements indicate that in our sample the cause is a donor acceptor pair transition.