Thermal degradation of the green-emitting SrSi2O2N2:Eu2+ phosphor for solid state lighting

A phase pure SrSi2O2N2:Eu2+ green phosphor was synthesized by a solid state reaction through careful control of the Sr : Si ratio in the starting powder consisting of SrCO3, Si3N4 and Eu2O3. The thermal degradation of the phosphor was investigated by baking it at high temperatures for 2 h. The surface states of the samples before and after baking were analyzed by SEM, HRTEM, XPS, TGA/DTA, and high temperature in situ X-ray diffraction. The results showed that the thermal degradation became intense when the temperature was higher than 500 °C, and the degradation was caused by the formation of SrSiO3 on the particle surface and the oxidation of Eu2+ to Eu3+. It is suggested that the thermal stability can be enhanced by achieving high crystallinity as well as high phase purity of the phosphor.