Single GaN quantum wells in the nearly lattice-matched GaN/Al1−xInxN system have been studied using photoluminescence (PL) and PL excitation (PLE) spectroscopy. The structures were grown on free-standing GaN and sapphire substrates. Selectively excited PL is able to distinguish luminescence originating from the wells, barriers and the underlying GaN buffer layers. The PL spectra show that the quantum well transition energy decreases as the well-width increases. This manifestation of the quantum confined Stark effect (QCSE) results from intense spontaneous polarization fields, which are present even in the absence of strain in the QW layer. Power dependent PL measurements provide information on the screening of the internal fields. PLE data provide an estimation of the band gap and enable one to determine the energy shift between emission and absorption in the Al1−xInxN barriers.