Strained nanowires with varying InAs/InP core/shell thicknesses were grown using Chemical Beam Epitaxy. Microphotoluminescence spectroscopy, performed at low temperature, was then used to study the optical properties of single wires. Emission from the InAs core was observed and its dependence on the shell thickness/core diameter ratio was investigated. We found that it is possible to tune the emission energy towards 0.8 eV by controlling this ratio. We have compared the measured energies with calculated energies. Our findings are consistent with the wires having a hexagonal crystal structure. (c) 2005 Elsevier B.V. All rights reserved.