We report a study of the luminescence properties of coherently strained GaAs1-xNx grown on GaAs by metalorganic molecular beam epitaxy. Well-defined photoluminescence was observed in samples with a nitrogen concentration up to 3%. Samples subjected to thermal anneals, investigated by x-ray diffraction and photoluminescence, show increased nitrogen incorporation and significant improvements in the luminescence efficiency. A band-gap reduction of more than 400 meV, compared to GaAs, is observed for a nitrogen concentration of ∼3%. For the range of nitrogen concentrations investigated here, the band gap follows predictions of the dielectric model of Van Vechten [J. A. Van Vechten and T. K. Bergstresser, Phys. Rev. B 1, 3351 (1970), and references therein].