Super stable (Ba,Sr)LuAl₂Si₂O₂N₅:Ce³⁺,Eu²⁺ phosphors

Phosphors suffer from decreasing light output due to degradation on exposure to heat, oxygen and water during the device fabrication process and in the working environment. Here, we report a series of (Ba,Sr)LuAl₂Si₂O₂N₅:Ce³⁺,Eu²⁺ phosphors which retain their initial luminescence intensity after being annealed in air at up to 800 °C or immersed in water for 5 days. Powder X-ray diffraction for fresh and annealed samples and thermogravimetric/differential thermal analysis confirmed the high stability of the host lattice of (Ba,Sr)LuAl₂Si₂O₂N₅. Electron spin resonance showed that the majority of Eu remained in the divalent state even after heating at 800 °C in air. The robust host lattice and stable valence of the activators are responsible for the high stability of (Ba,Sr)LuAl₂Si₂O₂N₅:Ce³⁺,Eu²⁺ phosphors. The high chemical stability originates from the featured star-like N[(Al/Si)(O/N)₃]₄ building block and the condensed three dimensional rigid framework. The (Ba,Sr)LuAl₂Si₂O₂N₅:Ce³⁺,Eu²⁺ phosphors are potential candidates for lighting and display applications, especially for those that need high temperature treatment in the packaging process.