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The core photoluminescence emission of MOVPE‐grown GaAs–Al0.33Ga0.67As core–shell nanowires is studied as function of the relevant geometrical parameter of these nanostructures, namely the shell‐thickness to core‐radius ratio hs/Rc. The energy of the dominant emission peak was compared with values of the GaAs heavy‐ and light‐hole excitons redshifted by a uniaxial tensile strain, the latter calculated assuming perfect coherence at the core/shell interface and elastic energy equilibrium within the nanowires. Good agreement is obtained for hs/Rc < 1, the intrinsic strain‐free excitonic emission being identified at 1.510 eV, and further ascribed to bound heavy‐hole excitons. For hs/Rc > 1 increasingly larger redshifts (up to ∼9 meV in excess of values calculated based on our elastic strain model) are observed, and tentatively ascribed to shell‐dependent exciton localization effects. Experimental and calculated bound exciton peak energies for GaAs–Al0.33Ga0.67As core–shell nanowires as function of their shell‐thickness to core‐radius ratio hs/Rc. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Part of Focus Issue on “Semiconductor Nanowires” (Eds.: Chennupati Jagadish, Lutz Geelhaar, Silvija Gradecak) The core photoluminescence emission of MOVPE‐grown GaAs–AlGaAs core–shell nanowires is studied as function of the relevant geometrical parameters of these nanostructures. The energy of the nanowire dominant excitonic peak is compared with theoretical calculations based on an elastic energy equilibrium model. This allowed evaluating the contribution of elastic strain and possible localization effects to the redshift of exciton emission with AlGaAs shell thickness. [ABSTRACT FROM AUTHOR]