Combustion synthesis of Ca-α-SiAlON:Eu2+ phosphors with different Ca concentrations and diluent ratios. Issue 15 (15th October 2017)

• Record Type: Journal Article
• Authors: Saito, Genki; Kunisada, Yuji; Sakaguchi, Norihito; Nomura, Takahiro; Akiyama, Tomohiro
• Is Part Of: Ceramics international. Volume 43:Issue 15(2017)
• Page Start: 12396
• Page End: 12401
• Publication Date: 2017-10-15
• Subjects: Phosphor -- Oxynitride -- SiAlON -- Combustion synthesis; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2017.06.106
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: Yellow Ca-α-SiAlON:Eu 2+ phosphors for white light-emitting diodes (LEDs) were synthesized by a facile combustion synthesis method using CaO, Eu2 O3, α-Si3 N4, Si, and Al as raw materials. Ca concentrations and diluent ratios were optimized to improve their luminescence properties. The lattice constant and luminescence properties improved as x increased from 0.4 to 1.2 in Ca x Si 12 − (m+n) Al m+n O n N 16−n :Eu0.06 . The optimum value was x = 1.2. Scanning transmission electron microscopy combined with energy dispersive X-ray analysis detected segregation of Ca and Eu at grain boundaries, which decreased luminescence behavior in the x = 1.4 sample. The influence of Si and Si3 N4 diluents was investigated by varying the diluent ratio φ = (CaO + Eu2 O3 + α-Si3 N4 )/(CaO + Eu2 O3 + α-Si3 N4 + Al + Si). Changes in temperature and flame propagation speed were measured during combustion synthesis using two thermocouples. When φ was less than 0.5, the combustion temperature exceeded 1600 °C and the synthesized material contained an amount of the high-temperature β-SiAlON phase. At φ > 0.7, the reaction temperature fell below 1200 °C, and unreacted raw materials remained. The optimum value of φ was 0.6. The internal quantum efficiency of the product synthesized at x = 1.2 and φ = 0.6 was approximately 35% under 450-nm excitation. According to electron probe X-ray microanalysis, composition varied within individual synthesized particles, which may explain the decrease in emission behavior relative to a commercial product.