Journal of Solid State Chemistry 173 (2003) 335–341 Synthesis and characterization of Gd 2 O 3 :Eu 3+ phosphor nanoparticles by a sol-lyophilization technique C. Louis, a R. Bazzi, a Marco A. Flores, a W. Zheng, a K. Lebbou, a, O. Tillement, a B. Mercier, a C. Dujardin, a and P. Perriat b a Physical Chemistry of Luminescent Materials, Claude Bernard/Lyon University, CNRS UMR 5620, Villeurbanne, Cedex 69622, France b UMR 5510 CNRS INSA of Lyon, France Received 26 September 2002; received in revised form 23 January 2003; accepted 1 February 2003 Abstract The characterization and luminescence properties of nanostructured Gd 2 O 3 :Eu 3+ phosphors synthesized by a sol-lyophilization process are presented. After preparation of gadolinium-based sols from gadolinium nitrate and ammonium hydroxide, the so- prepared sols were freeze dried at 101C and calcinated at different temperatures. For temperatures lower than 1300K, highly crystalline samples with the cubic structure can be obtained without concomitant grain growth of the particles (o50nm). The luminescence spectra contain all possible transitions of Eu 3+ with C 2 symmetry and present two major features: an increase of the luminescenceefficienciesofthephosphorsincomparisonwiththatobtainedbysolid-statereactionandthepresenceofanadditional peak at about 609nm at the vicinity of the 5 D 0 - 7 F 0y4 transition. r 2003 Elsevier Science (USA). All rights reserved. Keywords: Lyophilization; Nanoparticles; Crystalline; Phosphors; Luminescence 1. Introduction The research of efficient and inexpensive nanoparti- cles is a challenging problem for the new materials generation [1–3].Theproductionofluminescentmateri- als for technology applications requires strict control overtheirpowdercharacteristicswhichincludechemical homogeneity, low-impurity levels and a sub-micrometer particle size with a narrow distribution [4,5]. The conventional phosphor production through high tem- perature solid-state reactions typically results in particle sizes of 5–20mm [6]. Aiming at nanometer-sized oxide particles, more advanced types of synthesis are then required [7–9].Sincethegadoliniumoxidepresentsgood luminescent properties when doped with rare-earth ions (Eu 3+ , Tb 3+ ) [10–12], the oxide phosphor materials could be a good example to improve the luminescence properties and to extend the application field to a large domain [13,14].Theaimofthispaperistoevaluatethe possibility of synthesis of Gd 2 O 3 :Eu 3+ sub-micrometer sized phosphors with improved luminescent properties using a sol-lyophilization technique. To obtain such nanometer-sized phosphors, low-temperature processes are preferred to those involving the comminution of samples prepared by classical solid-state reactions: indeed, only these soft processes permit to obtain samples with well-controlled composition, narrow par- ticle size distribution and to avoid the defects generally induced by high-energy ball milling. These oxide phosphormaterialscouldbeagoodexampletoimprove the luminescence properties and to extend the applica- tion field to a large domain [15]. Such low-temperature processes have already been investigated for the preparation of nanosized phosphors in the case of yttrium-based phosphors [16,17]. They mainly consist of sol–gel techniques. However, the sol–gel processes involve precursors or solvents which contain organic parts which may induce uncontrolled grain growth during their exothermic degradation. They also suffer from the residual pollution of the samples, which strongly decreases the luminescent efficiency. Furthermore, they involve the formation of a gel whose structure may greatly influence the final particle size. Indeed, the gel in solution is characterized by an interconnected and rigid network having ARTICLE IN PRESS  Corresponding author. Fax: +33-4-72-43-12-33. E-mail address: lebbou@univ-lyon1.fr (K. Lebbou). 0022-4596/03/$-see front matter r 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0022-4596(03)00107-5