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Stefan Bernhard Department of Chemistry, Princeton University, Princeton, New Jersey 08544

Nan Yao Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey 08544 (Received 22 April 2005; accepted 28 June 2005)

Y2O3:Eu nanophosphors were prepared by flame synthesis using ethanol or water as precursor solutions. The effects of precursor solvents and flame temperature on particle size, morphology, and photoluminescence intensity were investigated. The results showed that flame synthesis using ethanol solution could produce nanoparticles with better homogeneity, smoother surface structure, and stronger photoluminescence intensity than using water. It was found that the concentration quenching limit of the as-prepared nanophosphors from both ethanol and water solution was 18 mol% Eu, which is higher than the reported limit at similar particle size. The x-ray diffraction (XRD) spectra showed that the ethanol precursor solvent produced monoclinic phase Y2O3:Eu nanoparticles at a lower flame temperature than previously reported. It was also shown that the particle size could be controlled by varying the precursor concentration and flame temperature.

I. INTRODUCTION

Nanoparticles have become a research focus in terms of both their fundamental and practical importance, especially in the case of luminescent materials.1–6 Phosphorous nanoparticles exhibit unique chemical and physical properties compared to their bulk materials. These properties are halfway between molecular and bulk solid state structures.1 For example, quantum confinement effects, which bring electrons to higher energy levels, can lead to novel optoelectronic properties.7 Due to these unique properties, many potential applications in optical, electrical, biological, chemical, and mechanical areas can be developed.1,4 Moreover, the emission lifetime, luminescent efficiency, and concentration quenching of the luminescent particles strongly depends on particle size, crystal structure, and hydroxyl residuals.2,3 Among numerous phosphors, europium-doped yttrium oxide (Y2O3:Eu) has attracted much attention as a good red phosphor that is widely used in optical displays and

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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0364 2960

http://journals.cambridge.org

J. Mater. Res., Vol. 20, No. 11, Nov 2005 Downloaded: 01 Dec 2014

lighting applications.8 Under ultraviolet (UV) excitation, Y2O3:Eu gives a sharp red emission line at 611 nm, and the luminescence efficiency is high because its charge transfer transition is located in the UV range.8 Nanoscale Y2O3:Eu phosphor has shown significant promise in high-resolution displays (field emission display, flat panel display, thin film electroluminescence panel, etc.) because the quantum efficiency of doped nanocrystals increases as the particle size decreases.2,9 Various methods, such as sol-gel techniques,10 homogeneous precipitation,11 thermal hydrolysis,12 laser-heated evaporation,13 chemical vapor synthesis,14 microe