A photolummescence (PL) study of Be and Au ion-implanted GaN is presented GaN samples were implanted and selectively annealed prior to excitation by a HeCd laser. The resulting luminescence was dispersed by a grating spectrometer and detected using a photomultiplier tube. Be is proposed to form a shallow acceptor in GaN and is thus critical to device development and performance. From analysis of the PL spectra, a shallow level appears consistently following an annealing procedure. It has been observed th a t Au impurities in Si introduce centres near the middle of the bandgap which act as very effective lifetime killers. A PL study of the effect of Au impurities in GaN is presented. A series of bands occur in the region 1 5eV to 2 4eV with peaks at 1 7eV and 2 3eV. A parallel aspect of the work involved the development of a photolummescence excitation (PLE) spectroscopy system with the ultimate aim of investigating impurity centres m doped GaN. The PLE system consisted of a tunable laser source, existing photolummescence equipment and a computer control / acquisition system PLE is used to investigate the below bandgap optical characteristics of emission bands and levels. Preliminary results using this equipment on well characterised ruby samples are presented along with a study of Be and Au defects in GaN.