Quantum dots (QDs) have been shown to improve the efficiency and optical properties of opto- electronic devices compared to two dimensional quantum wells in the active region. The formation of self-assembled GaN nanostructures on aluminum nitride (AlN) grown on sapphire substrates by Metal Organic Chemical Vapor deposition (MOCVD) was explored. This paper reports on the effect of in-situ activation in nitrogen atmosphere on MOCVD grown GaN nanostructures. The effect of introducing manganese in these nanostructures was also studied. Optically active nanostructures were successfully obtained. A blue shift is observed in the photoluminescence data with a decrease in nanostructure size.