Structure and luminescence of Ca2Si5N8:Eu2+ phosphor for warm white light-emitting diodes
Wei Xiao-Dan(魏小丹)a), Cai Li-Yan(蔡丽艳)a), Lu Fa-Chun(鲁法春)a), Chen Xiao-Long(陈小龙)b), Chen Xue-Yuan(陈学元)c), and Liu Quan-Lin(刘泉林)a)†
a School of Materials Science & Engineering and State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China; b Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; c Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China
Abstract We have synthesized Ca2Si5N8:Eu2+ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca2Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8:Eu2+ phosphor shows a broad red emission band centred at ～1.97 eV--2.01 eV. The gravity centre of the excitation band is located at 3.0 eV--3.31 eV. The centroid shift of the 5d levels of Eu2+ is determined to be ～1.17 eV, and the red-shift of the lowest absorption band to be ～0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang--Rhys parameter S = 6.0, the phonon energy $\hbar \nu =52$ meV, and the Stokes shift $\Delta S=0.57$ eV are obtained. The emission intensity maximum occurring at ～200 K can be explained by a trapping effect. Both photoluminescence (PL) emission intensity and decay time decrease with temperature increasing beyond 200~K due to the non-radiative process.
Received: 24 October 2008
Revised: 19 January 2009
Accepted manuscript online:
Fund: Project supported by the National
Natural Science Foundation of China (Grant No 50672007), Program for
the New Century Excellent Talents of China (Grant No NCET-06-0082),
and the National Basic
Research Program of China (Grant No 2007CB936202).
Cite this article:
Wei Xiao-Dan(魏小丹), Cai Li-Yan(蔡丽艳), Lu Fa-Chun(鲁法春), Chen Xiao-Long(陈小龙), Chen Xue-Yuan(陈学元), and Liu Quan-Lin(刘泉林) Structure and luminescence of Ca2Si5N8:Eu2+ phosphor for warm white light-emitting diodes 2009 Chin. Phys. B 18 3555
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