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Rong-Jun Xiea) and Naoto Hirosaki Nano Ceramics Center, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan

T. Sekiguchi Advanced Electronic Materials Center, National Institute for Materials Science (NIMS), Tsukuba 305-0044, Japan (Received 5 February 2007; accepted 27 March 2007)

Ce3+-activated lanthanide silicon oxynitride (La5Si3O12N, La4SiO7N2, LaSiO2N, and La3Si8O4N11) phosphors were prepared by firing the mixture of La2O3, Si3N4, SiO2, and CeO2 at 1500–1600 °C under a 0.5 MPa nitrogen atmosphere. Diffuse reflection spectrum, photoluminescence spectra, and temperature-dependent luminescence of these phosphors are presented in this work. A blue emission of Ce3+ in all lanthanide silicon oxynitrides was observed under ultraviolet irradiation, which is strongest in La3Si8O4N11:Ce3+. The concentration quenching and thermal quenching of the samples were discussed.

I. INTRODUCTION

The unique spectroscopic properties of rare-earth ions in different host lattices have prompted the development of rare-earth luminescent materials for a variety of applications, including lamp phosphors, cathode ray tube phosphors, radiation monitoring, lasers, scintillators, and white light-emitting diodes (LEDs). Recently, rare-earth activated nitride/oxynitride phosphors, a new class of luminescent materials, have attracted significant attention due to their promising photoluminescent properties and potential applications in white light-emitting diodes (LEDs).1–14 The coordination of rare-earth ions to nitrogen in oxynitride/nitrides results in large crystal-field splitting and strong nephelauxity effect, which finally leads to long-wavelength emission and excitation that differs greatly from that of traditional oxidic luminescent materials. For example, under blue-light excitation Eu2+activated ␤-sialon,14 MSi2O2N2 (M ⳱ Ca, Sr, Ba),10 ␣-sialon,3–9,13 M2Si5N8 (M ⳱ Ca, Sr, Ba),1,15 and CaSiAlN316 show highly efficient green to red emissions. These phosphors have been used in attempts to prepare white LEDs when coupled to a blue LED chip. Warm to cool white lights can be achieved by using a single

a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0231 J. Mater. Res., Vol. 22, No. 7, Jul 2007

http://journals.cambridge.org

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yellow-emitting ␣-sialon:Eu 2+ phosphor, 5,17–19 and white LEDs with high color rendering index can be fabricated by using red and green nitride phosphors simultaneously.19–21 The interesting luminescent properties and potential applications of oxynitride/nitride phosphors in electronic devices have greatly stimulated the study of their preparation, structural characterization, luminescence, and applications. However, due to difficulties in preparation of phase-pure materials and the requirements of high-pressure nitrogen gas and high temperature (>1400 °C), reports on luminescence of oxynitride/ nitride materials are very limited. Similar to Eu2+, the emission of Ce3+ is characteristic of broad band. Furthermore, i