This paper reports the low temperature photoluminescence (PL) characteristics of GaAsN grown by radio frequency nitrogen plasma-assisted solid source molecular beam epitaxy. It is found that the PL peak of GaAsN at low temperature is not originated from band-to-band transitions, but from localized exciton recombinations, even though the GaAsN material is of good crystalline quality as verified by reflection high-energy electron diffraction and X-ray diffraction measurements. The interstitial N-As complex and defects related to the broad low energy-tail in the PL spectrum could be effectively removed by thermal annealing. The red-shift in the PL peak of GaAsN after annealing is to the best of our knowledge reported for the first time. This phenomenon depends on the growth conditions, in particular the nitrogen flux. The red-shift in the PL peak energy is useful for extending the GaAs-based nitride material to long wavelength applications. It is also noticeable that the full-width at half maximum of PL peak from GaAsN decreases linearly with the increasing annealing temperatures. (C) 2003 Elsevier Science B.V. All rights reserved.