Near-lattice-matched GaN Al1-x Inx N single quantum wells, grown using both free-standing GaN and conventional GaN-on-sapphire substrates, are studied by photoluminescence (PL) and PL excitation spectroscopies. PL spectra distinguish luminescence originating in the wells, barriers, and underlying GaN buffer layers. The spectra also reveal significant differences between structures grown simultaneously on the different substrates. The quantum well transition energy decreases as the well width increases due to the intense in-built electric fields, estimated to be 3.0±0.5 MeVcm, that persist in strain free GaN Al1-x Inx N. Screening of these fields is studied using the excitation power dependence of the PL. © 2008 American Institute of Physics.