Nanoparticles of a doped oxide phosphor prepared by direct-spray pyrolysis
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Tae Oh Kim School of Civil and Environmental Engineering, Kumoh National University of Technology, Kyungbuk 730-710, Korea (Received 17 May 2004; accepted 20 August 2004)
A gas-phase synthesis route based on spray pyrolysis with a residence/heating time of less than 0.1 s was designed to directly prepare Eu-doped Y2O3 phosphor nanoparticles. The average size of the phosphor particles decreased from the submicron size to around 10 nm when the concentration of the starting solution was increased. By increasing the operating temperature, from 1500 to 1700 °C, the submicron-particles were converted into a nano-particle phosphor, and their photoluminescence intensities at 611 nm (254-nm excitation) were greatly improved. This synthesis procedure has considerable potential for preparing a variety of doped luminescent nanoparticles without the need for post-treatment processing.
I. INTRODUCTION
The development of new types of devices has increased the need for phosphors with new or enhanced properties. Most commercial phosphor particles currently available on the market are prepared by solid-state reactions and in a size range of 2–10 m. On the other hand, for extending phosphors to applications with higher resolution, smaller particles would be desirable. A study of a doped nanocrystalline phosphor in the single-nanometer range (less than 10 nm in size) with a high luminescent efficiency has been reported for the doped semiconductor ZnS:Mn2+ 1 and the insulator Y2O3 with a Tb3+ or Eu3+ dopant.2 Y2O3:Eu3+ materials are some of the most frequently used phosphors in displays and lighting applications. To prepare doped nanocrystalline phosphors, including Eu3+-doped Y2O3, from a single nanometer to a few 10 nm, wet chemical methods are typically used.3–5 A post heat treatment is required to obtain the desired crystal structure as well as to control the size of (agglomerated) particles. Various studies of synthesis techniques for preparing doped nanocrystalline phosphors, such as gas condensation technique,6–8,combustion,9 and thin film chemical vapor deposition10,11 have been reported. At this time, the production of an agglomerate-free, dry
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0457 3534
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 12, Dec 2004 Downloaded: 11 Jun 2014
(powder) phosphor in the sub-100-nm range that exhibits high quality luminescence properties continues to be a problem. The spray pyrolysis (SP) method is a gas-phase route based on a droplet-to-particle conversion. Inside the aerosol reactor, each droplet has the same composition; thus the desired phosphor particles can be readily synthesized by controlling the composition of the starting solutions. Phosphors prepared by the SP method show good characteristics such as a high purity, a spherical shape, and non-aggregation characteristics.12 The concept or the basis of the SP process assumes that one droplet forms one product particle. The average size and size distribution o
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