This main aim of this thesis is to study the photoluminescence (PL) properties of Gallium Nitride (GaN) grown by either the solid- or the liquid- target Pulsed Laser Deposition (PLD) technique. Most thin films were deposited on sapphire(OOOl) substrate m a pure nitrogen (N2) atmosphere GaAs(OOl) was also used as a substrate for the first time. The properties of the material systems were characterized using PL, X-Ray diffraction (XRD), Raman spectroscopy and atomic force microscopy (AFM). The expansion dynamics of Ga and GaN laser-ablation plumes were also studied using time- resolved extreme ultraviolet dual laser photoabsorption (DLP) spectroscopy. The PL, XRD and Raman results indicated the possibility of a mixed cubic- and hexagonal- structure in GaN grown using the solid target PLD system PL full width at half maximum (FWHM) as narrow as -9 meV for the donor-exciton transitions (D-X) was achieved for GaN/sapphire(0001) grown by liquid target PLD system. Significantly enhanced low temperature PL emissions at 3 361 eV (I3) and 3 310eV (I4 ) were observed for the matenal deposited on a GaAs(OOl) substrate at ~800°C. A model has been proposed to explain the emission mechanism for I3 and I4 in which the electrons and holes are confined in cubic inclusions within the hexagonal matenal, analogously to a type 1 quantum well. The DLP results showed the marked difference between Ga and GaN laser-ablation plumes, and suggested that metallic Ga is a more suitable target matenal for the PLD growth of GaN compared to a GaN target.