Nanocrystalline Rare Earth-doped Gallium Nitride Phosphor Powders
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Nanocrystalline Rare Earth-doped Gallium Nitride Phosphor Powders G.A. Hirata1, J. Tao2, P. Chen2, K.C. Mishra3 and J. McKittrick2 1 CCMC-UNAM, Ensenada, B.C. Mexico, C.P. 22860 2 Department of Mechanical and Aerospace Engineering and Materials Science and Engineering Program, University of California at San Diego, La Jolla, CA 92093-0411 3 Osram Sylvania Central Research, Beverly, MA 01915
ABSTRACT We report on the fabrication and luminescent properties of rare earth-doped gallium nitride (GaN) phosphor powders. Single phase GaN and GaN:RE3+ powders were prepared by using a novel chemical route. In this work a new method for the synthesis of high purity, single phase doped GaN powders is reported. (Ga1-xREx)N powders are obtained by dissolving metal nitrates (Ga(NO3)3, (RE(NO3)3) in deionized water and an organic fuel (hydrazine) in order to form a gallium/RE amorphous/nanocrystalline powder. The RE-oxide powders are then reacted with heated ammonia at different temperatures and processing times producing GaN:RE phosphors. X-ray diffraction analysis showed that single phase GaN powders are formed. Preliminary results show (Ga0.95Eu0.05)N powders are luminescent, with the main emission occurring at 611 nm which is due to the 5D0→7F2 transitions in Eu3+. High-purity GaN powders are obtained according to Xray photoelectron spectroscopy (XPS) chemical analysis. Low-temperature cathodoluminescence and photoluminescence measurements indicate that the emission at λ=611 nm is originated from energy transfer from the host to the rare earth ion and to a direct excitation to the Eu3+ electronic levels. This method can be used to obtain red-luminescence GaN:Eu3+ and other rare earth (e.g. Er, Tb, Tm)-doped GaN powders to produce green and blue luminescence as well.
INTRODUCTION In the last decade III-nitrides-based (e.g. gallium nitride) materials have attracted special attention due to the great performance obtained recently in novel optoelectronic applications such as the blue diode [1] and electroluminescent devices [2,3]. More recently, there has been a quest for new phosphor materials with better properties to be used as electroluminescent (EL) phosphors and eventually find a way to replace the currently ZnS-based phosphors. Gallium nitride (GaN) promises to be a suitable material that can overcome some of these technological problems. The robust nature of GaN and its ability to incorporate a large concentration of rare earth dopants have made it an attractive candidate for electroluminescent displays in the form of thin films and powders. The advantage of using GaN for EL phosphor technologies is due mainly to its robust nature while being comparable to ZnS in all other physical, optical and electrical properties. It is
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known to have greater chemical stability, carrier generation and physical stability over a wide temperature range compared to II-VI’s. It has a direct band gap of 3.42 eV and exhibits a high level of optical activity even under high defect densities [4]. Light emitting diodes (LED’s) a
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