Tb3+-doped ZrO2 samples were prepared both as pure compounds and as a nanocomposite made up of sub-5 nm crystalline nanoparticles developed in an amorphous silica matrix. The materials were characterized by using HRTEM, XRD and luminescence spectroscopy. The amount of terbium crystallized into the zirconia lattice was determined by the Rietveld method. A significant improvement of the life time was observed in the nanocomposite with respect to the pure lanthanide doped zirconia particles despite of the very high (about 20 mol%) rare earth concentration developed. (c) 2006 Elsevier B.V. All rights reserved.