Structural evolutions and significantly reduced thermal degradation of red-emitting Sr2Si5N8:Eu2+via carbon doping. Issue 35 (27th July 2017)

• Record Type: Journal Article
• Authors: Liu, Lihong; Wang, Le; Li, Yuanqiang; Zhang, Chenning; Cho, Yujin; Or, Siu Wing; Zhou, Tianliang; Takeda, Takashi; Hirosaki, Naoto; Xie, Rong-Jun
• Is Part Of: Journal of materials chemistry. Volume 5:Issue 35(2017)
• Page Start: 8927
• Page End: 8935
• Publication Date: 2017-07-27
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c7tc02908j
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Carbon-doping in Sr2 Si5 N8 :Eu 2+ results in enhanced reduction of Eu 3+ and the covalence of Eu–(N, C) bonds, finally leading to enhanced thermal degradation. Abstract : A red-emitting nitridosilicate phosphor, Sr2 Si5 N8 :Eu 2+, 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 Sr2 Si5 N8 lattice to form thermally robust carbidonitride phosphors (Sr2 Si5 C x N8−4 x /3 :Eu 2+ ). 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 Eu 3+ 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 Eu 2+ . Thanks to the increased oxidation resistance of Eu 2+ 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.