The influence of nitrogen content on the optical properties of InGaAsN/GaAs single quantum wells (SQWs) with nitrogen concentration up to 5.2% and relatively high indium content have been investigated by photoreflectance (PR) and photoluminescence (PL) spectroscopy. The PR measurements have allowed us to observe, besides of the fundamental I I H optical transition, transitions between excited states in QWs. The identification of optical transitions present in PR spectra has been possible due to the theoretical calculations based on the envelope function model. We have found the relatively high red shift of all optical transitions with increasing nitrogen content. The temperature dependence of PL peak energy have been investigated, too. The thermal stability of PL peak energy is stronger for structures with higher N content. Fitting with Varshni empirical relation to PL data we have found that at low temperatures carriers are localised. For structures with high nitrogen content we observed S-shaped energy peak behaviour. (C) 2002 Elsevier Science Ltd. All rights reserved.