This study systematically investigates the effects of magnetic field on the defects suppression in hydrothermally synthesized ZnO nanorods. A clear correlation between the crystalline quality and magnetic field-induced suppression of defect-related emission intensity is demonstrated. The density of defects in the nanorods is reduced by increasing the strength of the applied magnetic field, drastically reducing the intensity of visible photoluminescence. The mechanism of the magnetic field-induced suppression of defect-related emissions in hydrothermally synthesized nanorods is explained by a model-based analysis of the paths of the electrical currents and the resulting Lorentz force in the related neighboring pair of rolling cellular patterns that are generated from Rayleigh-Benard convection. This work provides a new means of controlling the defects in nanomaterials, improving the crystalline quality of such materials, and thereby adjusting their light-emitting properties. (C) 2014 Elsevier B.V. All rights reserved.