Due to its non-destructive and its micro-spatial resolution, Raman spectroscopy is a powerful tool for a rapid structural and compositional characterization of nanoscale materials. Here, by combining the compositional dependence of the Raman peaks with the existence of photonic modes in the nanowires, we address the composition inhomogeneities of AlxGa1�xAs/GaAs core/shell structures. The experimental results are validated with complementary chemical composition maps of the nanowire cross-sections and finite-difference time-domain simulations of the photonic modes.