Aerosol Science 37 (2006) 402 – 412 www.elsevier.com/locate/jaerosci Photoluminescence of Eu 3+ :Y 2 O 3 as an indication of crystal structure and particle size in nanoparticles synthesized by flame spray pyrolysis Dosi Dosev, Bing Guo, Ian M. Kennedy ∗ Department of Mechanical and Aeronautical Engineering, University of California, Davis, CA 95616, USA Received 25 September 2004; received in revised form 3 May 2005; accepted 18 August 2005 Dedicated to the 70th birthday of Professor Daniel E. Rosner Abstract Nanoparticles of europium-doped yttrium oxide (Eu: Y 2 O 3 ) were synthesized by flame spray pyrolysis. The nanoparticles were separated by centrifugation into two size groups (5–60 nm and 50–200 nm), each characterized by laser induced fluorescence spectroscopy, Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The fluorescence spectra, the electron diffraction pattern, and the XRD pattern of the large particles were typical of the stable cubic (Mn 2 O 3 type) phase of bulk Y 2 O 3 while those of small particles were quite different and indicated the possible presence of higher density metastable mixed phases—including monoclinic with some indication of a face-centered cubic phase. The size dependence of the particle properties could be attributable to the effect of surface free energy that elevated the internal particle pressure as size decreased. Doping with the lanthanide ion provided a new and useful diagnostic method for determining the crystal structure of flame-synthesized materials.  2005 Elsevier Ltd. All rights reserved. Keywords: Nanoparticles; Yttrium; Europium; Fluorescence; Spray pyrolysis 1. Introduction Gas processing of nanostructured materials offers significant advantages over liquid phase chemistry. The process is scalable to high production rates; it can yield material of high purity; a wide range of materials can be formed; and the process can be designed to be both environmentally benign, with no toxic by-products, and energetically efficient. The important characteristics of the product include the particle size distribution, composition and morphology. Rosner, McGraw, and Tandon (2003) and Rosner and Pyykonen (2002) have recognized the importance of multiple variables in the design and operation of gas phase synthesis processes and have developed an appropriate formalism for treating this problem numerically. Crystal structure may ultimately be predictable with such methods, and in some materials and applications, such as yttrium oxide (yttria), the crystal phase may be an important process variable. Yttrium oxide (Y 2 O 3 ) has often been used as a host material for phosphors and other optical applications and is conventionally processed from micron-sized powders that almost always contain small amounts of impurities. While ∗ Corresponding author. Tel.: +1 530 752 2796; fax: +1 120 620 22448. E-mail address: imkennedy@ucdavis.edu (I.M. Kennedy). 0021-8502/$ - see front matter  2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaerosci.2005.08.009