We report on the effects of post-growth annealing on the photoluminescence properties of Ga(In, N)As/GaAs(N) quantum wells with N and In concentrations in the range of 2.5% and 30-40%, respectively. The low growth temperature used to prevent the decomposition of the unstable alloy is mainly responsible for the high density of nonradiative defects. The concomitant presence of both In and N induces carrier localization in the quaternary alloy and a strong blueshift after post-growth annealing. Annealing reduces the non-radiative recombination centers and allows an atomic reorganization (responsible for the blueshift). After annealing, the smoothing of the band structure and the improved composition homogeneity induce a decrease of the localization. Finally, we demonstrate emission near 1.5 mum at room temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.