In this thesis, single zincblende GaAs nanowires grown by molecular beam epitaxy using the self-catalyzed approach were studied with m-photoluminescence spectroscopy in order to assess the optical quality of self-catalyzed GaAs nanowires grown for the first time at NTNU and to compare the optical properties of self-catalyzed GaAs nanowires with Au-assisted GaAs nanowires and bulk GaAs references. The low temperature and temperaturedependence measurements revealed type II recombinations between zincblende and wurtzite segments occurring at the nanowire tips, however it was established that radiative recombination does not take place in the zincblende GaAs nanowire core. As the thesis progressed, valuable feedback was given to the growers in order to optimize nanowire growth conditions. The thesis builds upon data from earlier work within this project andprovides a foundation for future work on self-catalyzed GaAs nanowire devices at NTNU.