A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd2O3 codoped with Tb3+, Eu3+ increase their light yield by energy transfer between Tb3+ and Eu3+. In this study, Gd2O3 nanopowders codoped with Eu3+ and Tb3+ (2.5 at.% Eu3+, and 0.005 and 0.01 at.% Tb3+) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd2O3Eu3+, Tb3+ by means of TGA, XRD, TEM and X-ray emission measurements. (C) 2009 Elsevier Ltd. All rights reserved.