The emission energies and their intensity distributions of excitonic radiative recombination in a non-uniform GaAs-based quantum well (QW) system are investigated by spatially resolved cathodoluminescence (CL) spectroscopy. By measuring the spectrally discriminated CL intensities originating from the different QWs as a function of excitation position, we are able to map out how the compositional distribution of the alloy barriers affects the CL intensities of the respective QW exciton bands. Surprisingly intense high-energy emission is observed due to the presence of an unintentionally introduced interface layer formed in the barrier heterostructure, when it is in resonance with the excited subband transition of a neighboring QW. (C) 2010 Elsevier B.V. All rights reserved.