Synthesis and characterization of Ce 3+ doped silica (SiO 2 ) nanoparticles L.F. Koao a , H.C. Swart a , R.I. Obed b , F.B. Dejene a,n a Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein, South Africa b Department of Physics, University of Ibadan, Ibadan, Nigeria article info Article history: Received 8 October 2009 Received in revised form 11 October 2010 Accepted 28 October 2010 Available online 13 January 2011 Keywords: Synthesis Nanoparticles Ce 3+ -doped silica Photoluminescence abstract A series of silica doped with different mol percentages of Ce 3+ concentration was synthesized using a sol–gel method to determine the dependence of photoluminescence wavelengths and intensity on the concentrations of the dopants. Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Rare-earths (REs) are insoluble in silica; due to this insolubility RE ions in silicate glasses enter as network modifiers and compete for non-bridging oxygen in order to complete their coordination. The morphological, structural, thermal and optical properties of the phosphors were characterized by X-ray diffraction, scanning electron microscopy, UV–vis absorp- tion, photoluminescence, thermogravimetric analyses and differential scanning calorimeter. Silica (SiO 2 ) gel containing Ce 3+ ions was sputter coated with Au (gold) in order to monitor surface morphology of the samples. The highest emission intensity was found for the sample with a composition of 0.5 mol% Ce 3+ . Cerium doped silica glasses had broad blue emission corresponding to the 2 D 3/2 – 2 F J transition at 448 nm but exhibited apparent concentration quenching above concentra- tions of 0.5 mol% Ce 3+ . & 2010 Elsevier B.V. All rights reserved. 1. Introduction The sol–gel technique that involves the simultaneous hydro- lysis and condensation reaction of the metal alkoxide [1] is one of the most common methods of synthesizing silica nanoparticles. It is an efficient technique for the synthesis of phosphors due to the good mixing of starting materials, and relatively low reaction temperature resulting in more homogeneous products than those obtained by the solid-state reaction synthesis method. It is well known that almost every element in the periodic table can be stuffed into glasses, to control its quality and opto-electronic properties. Glass hosts with their superior properties such as optical, flexible geometry, higher doping levels and fiberization capability are a viable alternative to crystal. Glass matrices also provide a wider tunability range because of varied site geometries available to the active species. Generally lanthanide ions, such as Ce 3+ , Eu 3+ , Er 3+ , etc., are incorporated in SnO 2 to improve the catalytic and luminescence efficiency [2–6]. Conventionally silica glasses are prepared at relatively higher temperatures, of the order of 500 1C. High temperature treatment of lanthanide doped nanoparticles results in lanthanide ion clustering leading to phase separation and nanoparticle sintering, thereby a reduction in surface area, which leads to a decrease in the luminescence efficiency due to self-quenching and poor photocatalytic activity. One of the ways to prevent the sintering of the lanthanide doped nanoparticles is to disperse the nanoparticles in matrices, such as SiO 2 , TiO 2 , etc., at relatively low temperatures. Cerium doped sol– gel silica glasses seem to be promising materials for diverse applications such as phosphors, lasers, amplifiers and radiation detection technologies [7,8]. Ce 3+ ions were widely used as activators in various oxides materials for its allowed optical transitions of 4f–5d. A strong overlap of the activator 5d orbitals with ligand orbital causes high sensitivity of their spectral characteristics to the local environment structure. Many research- ers have mentioned two main luminescent bands of Ce 3+ ions at 357 and 450 nm in the samples of Ce 3+ -doped glasses and crystals [9–11]. Both the bands were attributed to the 4f–5d transitions of triply charged cerium. There is still no doubtless conclusion about the relationship between the luminescence bands and the environment structure. In some Ce 3+ -doped materials, there was only one luminescence band with the maximum at 357 nm [10,11], but in other samples luminescence bands at 450 nm appeared [10]. The luminescence of Ce doped silica is influenced by factors such as the modification of the ligand field around the Ce 3+ ions in silica, presence of hydroxyl ions, energy transfer by cross relaxation and the concentration of dopants [12]. It was therefore of great interest to distinguish between the luminescence arising from Ce 3+ ions and of that arising from defect centers in the silica matrix. Thus, the purpose of this paper is to study the absorption and luminescent Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence 0022-2313/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2010.10.038 n Corresponding author. E-mail address: dejenebf@qwa.uovs.ac.za (F.B. Dejene). Journal of Luminescence 131 (2011) 1249–1254