This report reflects the results of heat treatment under various conditions on as-grown and ion implanted GaN. The PL spectrums of as-grown GaN and GaN with 400 Angstrom AlN cap were almost identical. This fact allows us to use PL analysis without AIN stripping. As-grown GaN and ion implanted with Mg+ and Si+ crystals were annealed at 1300 degreesC for 10 minutes in three different conditions: in flowing argon gas; in flowing ultra high purity nitrogen; and in a quartz capsule sealed with nitrogen gas. The results of FL, RES, SEM and TEM analysis show an advantage of GaN high temperature annealing in quartz capsules with nitrogen ambient as compared to annealing in argon and nitrogen gas flow. Encapsulation with nitrogen overpressure prevents the decomposition of the GaN crystal and the AIN capping film, and allows one to achieve optical activation of implanted Mg and Si after 1300 degreesC annealing.