Synthesis, composition optimization, and tunable red emission of CaAlSiN 3 :Eu 2+ phosphors for white light-emitting dio
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Xue-Jian Liua) The State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Jia-Qing Liu and Huili Li Engineering Research Center for Nanophotonics and Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, Shanghai 200062, China
Ri-Hua Mao Analysis and Testing Center for Inorganic Materials, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Zheng-Ren Huang The State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Rong-Jun Xieb),c) Sialon Group, Sialon Unit, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan (Received 15 February 2015; accepted 20 April 2015)
Ca0.98Eu0.02Al14d/3Si11dN3 (d 5 0–0.36) red-emitting phosphors were prepared by carbothermal reduction and nitridation method with stable and inexpensive CaCO3 as Ca source. Optimal nominal composition was obtained at d 5 0.18, showing intense emission peaked at 625 nm and high external quantum efficiency of 71%. The emission wave length could be successfully tuned from 630 to 606 nm with increasing d value. Ca0.98Eu0.02Al14d/3Si11dN3 phosphors provided two coordinated environments for Eu21 ions, resulting in two fitted Gaussian peaks. Energy transfer from Eu21 sites in Si-rich environments to those in Si/Al-equivalent modes has been confirmed by analysis of the decay curve of each peak. The decay behaviors suggested that energy transfer effect slowed with higher d value. Finally, warm white light was created by combining as-prepared red-emitting Ca0.98Eu0.02Al0.76Si1.18N3 and yellow-emitting YAG:Ce31 phosphors with a blue-emitting chip, exhibiting a color rendering index Ra of 91 at a low correlated color temperature of 3500 K with a luminous efficiency of 79 lm/W.
I. INTRODUCTION
In recent years, light-emitting diodes (LEDs) have attracted considerable interest owing to their superior properties such as high efficiency, low-voltage driving, long lifetime, great reliability, and environmental friendliness.1–3 Most commercially available white LEDs are fabricated by combining blue-emitting LED Contributing Editor: Zoltan Lences Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] c) This author was an editor of this focus issue the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2015.125 J. Mater. Res., Vol. 30, No. 19, Oct 14, 2015
chips (440–470 nm) with YAG:Ce31 yellow-emitting phosphor materials, but they show drawbacks of low color rendering index (CRI , 75) and high correlated color temperature (CCT . 4500 K) due to lack of red component in the spectral region.4–6 However, this issue can be improved by a slight addition of redemitting phosphors
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