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Issue 35, 2017
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Structural evolutions and significantly reduced thermal degradation of red-emitting Sr2Si5N8:Eu2+via carbon doping

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Abstract

A red-emitting nitridosilicate phosphor, Sr2Si5N8:Eu2+, shows very promising photoluminescence properties but exhibits serious thermal degradation, thus making it difficult to be used practically as a color converter in white light-emitting diodes (wLEDs). To alleviate this problem, we introduce carbon into the Sr2Si5N8 lattice to form thermally robust carbidonitride phosphors (Sr2Si5CxN8−4x/3:Eu2+). The carbon doping, evidenced by a variety of analytical techniques, leads to structural evolutions including lattice shrinkage, shortening of the average bond length of Eu–(C,N), and the removal of Eu3+ ions from the lattice. The photoluminescence intensity and quantum efficiency of phosphors are greatly improved by the carbon doping and reach the maximum at x = 0.5, dominantly owing to the enhanced absorption of Eu2+. Thanks to the increased oxidation resistance of Eu2+ due to the stronger covalency of Si–(C,N) and Sr(Eu)–(C,N) bonds, thermal degradation is significantly reduced from 16 to 0.8% when the carbon doping increases from x = 0 to 1.25. In addition, thermal quenching is also reduced by 10% at 300 °C and the quantum efficiency declines slowly with increasing temperature when carbon is substituted for nitrogen. At 300 °C, the internal quantum efficiencies are 55% and 62% for x = 0 and 0.5, respectively. The enhanced thermal stability of the carbon-doped sample is also confirmed by smaller variations in the luminous efficacy and color coordinates of monochromatic red LEDs.

Graphical abstract: Structural evolutions and significantly reduced thermal degradation of red-emitting Sr2Si5N8:Eu2+via carbon doping

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Publication details

The article was received on 28 Jun 2017, accepted on 17 Jul 2017 and first published on 17 Jul 2017


Article type: Paper
DOI: 10.1039/C7TC02908J
Citation: J. Mater. Chem. C, 2017,5, 8927-8935
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    Structural evolutions and significantly reduced thermal degradation of red-emitting Sr2Si5N8:Eu2+via carbon doping

    L. Liu, L. Wang, Y. Li, C. Zhang, Y. Cho, S. W. Or, T. Zhou, T. Takeda, N. Hirosaki and R. Xie, J. Mater. Chem. C, 2017, 5, 8927
    DOI: 10.1039/C7TC02908J

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