The Optimal Synthesis, Crystal Structure And Transformation, Luminescence Thermal Stability And Aging Mechanisms Of Nitride And Oxynitride Phosphors For LED Applications

White LEDs has become a new generation of environmental protection floodlight, its development received widespread attention. Phosphors is the most important raw material of white LEDs. Nitrogen and oxynitride phosphors can improve the efficiency of white LEDs effectively, improve the color rendering index and reduce the color temperature because of their high luminous efficiency, good thermal stability. We have been pursuiting high-performance phosphors, and the luminous efficiency of SrSi2O2N2:Eu2+ phosphor remains to be further improved. Now, Sr2Si5N8:Eu2+ phosphor synthesized by metal nitride has high costing, the thermal stability and aging mechanism is not clear.First, the article focused on SrSi2O2N2:Eu2+ phosphors, successfully explored the optimal synthetic process, based on the source of Sr compounds in raw material category, the ratio of Si3N4/SiO2 determined anionic groups, the types and levels of flux, reducing atmosphere and the reactor material. The internal quantum efficiency of SrSi2O2N2:Eu2+ phosphors reached 100% under 380nm excitation. There was Sr2Si5N8:Eu2+ impurity phase in SrSi2O2N2:Eu2+ which synthesized by carbon contained strontium source SrCO3 and SrC2O4. This paper further studied the technical route of SrSi2O2N2:Eu2+ under the condition of relatively low temperature 1400℃ using carbon thermal reduction and nitride reaction. The product contains a large number of Sr2Si5Ng:Eu2+ phase, and amorphous phase was observed with the help of HR-TEM in the fluorescent powder particle surface. Two pathways of carbon mixing were designed for synthesizd SrSi2O2N2:Eu2+. It provides an explanation for the mechanism of carbothermal reduction contributing to the synthesis of a Sr2SisNg:Eu2+ nitride phosphor, in terms of the heat released and propagated within the local region, which makes the actual temperature far higher than that determined in the reaction. Secondly, we explored different transformation path from oxides directly to Sr2Si5N8:Eu2+, from Sr2SiO4 to Sr2Si5N8:Eu2+ and from oxynitrogen to Sr2Si5N8:Eu2+, adopting SrO, Sr2SiO4, as precursor, respectively. The results show that the multi-step process helps to improve the purity of nitride target products by adding precursors crystallization degree and reducing the reaction activation energy, which exploring a low-cost, more effective way to synthesizing Sr2Si5N8:Eu2+ nitride phosphors. Finally, the article luminous performance and luminescence mechanism were researched adopted composition, time and temperature as three variables factors. The studies showed that the occupying state of excited states electrons changed significantly with different Eu2+ concentration, the auto-ionization from excited state to conduction band owe to thermal quenching mechanism, Eu2+ oxidation to Eu3+ is the major mechanism of thermal quenching and aging.The aim of this study is to obtain new technology for nitrogen phosphor, and improve the efficiency of nitrogen phosphor, thermal stability and reliability, offering guidance for further research.