The reversible phase transition VO2 exhibits, makes it a great candidate for energy efficient building glazing. Thus, a great need arises to optimize its optical and thermochromic properties, to be better suited for real smart window applications. In this study, thin films of Mg-doped VO2 have been successfully fabricated using RF reactive magnetron sputtering on commercially available products (glass coated-with SnO2 buffer layer) and, for the first time, on ZnO/glass substrates, as an alternative buffer layer. Doping concentration is found to strongly affect the thermochromic properties of the films, namely the transition temperature (T-c) and transmittance modulation ability. XRD and SEM studies have been performed to examine the structural and morphological features of the Mg-doped films. Optical transmittance measurements vs. temperature have been used to calculate T-c and hysteresis width of the transition, resulting in the lowest recorded T-c value of 35 degrees C, with respect to the literature, for an Mg doped film (6 at%). Furthermore, visible transmittance (T-lum) and solar modulation ability (Delta T-sol) have been determined for different doping concentration, and were correlated with an optical bandgap widening induced by the Mg preSence. Overall, the 3 at% Mg-doped film over ZnO/glass substrate presented the higher modulation ability of 4.5% and the best IR switching at 2000 nm with a value of 26%. (C) 2016 Elsevier B.V. All rights reserved.