Monodisperse Lu2O3:Eu3+ submicrospheres with the diameters ranging from 40 to 400 nm were obtained by the urea-based homogeneous precipitation technique with subsequent spheres crystallization during annealing. The inner structure, morphology of Lu2O3:Eu3+ polycrystalline spheres and thermal stability of the particles shape were investigated by means of transmission electron microscopy (TEM). X-ray diffractometry (XRD) and electron paramagnetic resonance (EPR). Eu3++doped lutetium oxide spheres were characterized by effective luminescence under X-ray excitation in the lambda=575-725 nm range corresponding to D-5(0)-> F-7(J) transitions (J=0-4) of Eu3+ ions. Experimental data showed that the X-ray luminescence efficiency increases with the increase of the crystallites size, which occurred by the annealing temperature and particles diameter. (C) 2011 Elsevier B.V. All rights reserved.