Journal of Colloid and Interface Science 273 (2004) 191–197 www.elsevier.com/locate/jcis Synthesis and properties of europium-based phosphors on the nanometer scale: Eu 2 O 3 , Gd 2 O 3 :Eu, and Y 2 O 3 :Eu R. Bazzi, a M.A. Flores, a C. Louis, a K. Lebbou, a W. Zhang, a,b C. Dujardin, a S. Roux, a B. Mercier, a G. Ledoux, a E. Bernstein, c P. Perriat, d,∗ and O. Tillement a a LPCML, Université Lyon 1, 43 Bd. du 11 Novembre 1918, 69622 Villeurbanne, France b Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China c DPM, Université Lyon 1, 43 Bd. du 11 Novembre 1918, 69622 Villeurbanne, France d GEMPPM, INSA de Lyon, 20 av. A. Einstein, 69621 Villeurbanne, France Received 9 July 2003; accepted 22 October 2003 Abstract Nanocrystals of oxides containing europium as the main constituent or as a doping element in RE 2 O 3 (RE = Y, Gd) have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by high-resolution TEM, absorption spectroscopy, and luminescence spectroscopy. The samples obtained consisted of concentrated and colloidally stable suspensions of luminescent oxide nanoparticles with an average grain diameter in the range 2–5 nm. The nanoparticles were found to be highly crystalline despite their ultrasmall size and the low temperature of 180 ◦ C applied during the synthesis. Upon UV excitation, the red luminescence relative to the 5 D 0 → 7 F n transition within the cubic form of RE 2 O 3 exhibits some important differences from that usually found in bulk materials.  2003 Elsevier Inc. All rights reserved. Keywords: Nanoparticles; Rare-earth oxides; Luminescent particle; Phosphors 1. Introduction Nanosize particles are under extensive study and have become a research focus in terms of both their funda- mental and technological importance [1,2]. This is partic- ularly true in the case of luminescent materials because of a quantum confinement effect which leads to novel optoelec- tronic properties. Emission lifetime, luminescence quantum efficiency, and concentration quenching have been found to depend strongly on the particle size in the nanometer range [3–5] and high efficiencies and ultrafast recombina- tion times have been observed in nanometer-sized nanocrys- tals [6]. In this context the study of colloidal solution of highly crystalline and well-separated luminescent nanoparti- cles presents a strong interest for fundamental studies since, contrary to aggregates in powders, the interactions between the particles can be neglected, and for simplicity of exper- iments also since, due to the absence of light scattering, * Corresponding author. E-mail address: pascal.perriat@insa-lyon.fr (P. Perriat). the colloids can be investigated with the same spectroscopic techniques than those used for bulk monocrystals. In the same way that chemical routes have been inten- sively investigated for the production of luminescent semi- conductor colloids, the preparation and characterization of doped nanooxide colloidal solution are receiving increasing attention. The most thoroughly investigated systems involve some doped ZnO nanoparticles [7]; some methods have been also recently proposed to synthesize colloids of lanthanide- doped phosphates and vanadates [8], europium-doped alu- mina [9] or strontium chloroapatite [10], Y 2 O 3 -based phos- phors [11–15], and lanthanide sesquioxides, Eu 2 O 3 [16] and Tb 2 O 3 [17]. In this paper, we propose an original approach to the syn- thesis of colloids with useful amounts of rare-earth oxide nanoparticles. It is based on the direct precipitation of oxides in a high boiling alcohol: diethylene glycol (DEG). Such a choice is motivated by several reasons: first, a nonaque- ous environment is necessary for avoiding the formation of hydroxide [18–20]; second, the DEG, which is expected to act as a surface capping agent [21], should prevent particle agglomeration; finally, its high boiling temperature should 0021-9797/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2003.10.031