Comment on 'Europium doping induced symmetry deviation and its impact on the second harmonic generation of doped ZnO nanowires'.

In Dhara et al 2014 Nanotechnology 25 225202, the authors reported on the synthesis of Eu-doped ZnO nanowires (NWs) and investigated the influence of Eu doping on the second harmonic generation (SHG). Maximum SHG was found to correlate strongly with the structural deformation attributed to Eu(3+) doping. In this comment, we show the deformation of interest is due to the presence of Eu(2+) dopants, based on both the experimental data presented by Dhara et al and ab-initio density functional theory calculations.