High temperature stability of Eu2+-activated nitride red phosphors

The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2+-activated nitride red phosphors, Sr1.95Si5N8:Eu0.05, Sr1.85Si5N8:Eu0.15 and Ca0.99AlSiN3:Eu0.01 phosphors were annealed at different temperatures (beyond 300 °C) to investigate the dependence of their luminescence performance and structure variability on the temperature. By photoluminescence spectra, X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC) analysis, the high temperature stability of the hosts and activator of the three samples were disclosed. With the annealing temperature increasing, the activator Eu2+ ions were firstly oxidized and then host in Sr1.95Si5N8:Eu0.05 and Sr1.85Si5N8:Eu0.15, but for Ca0.99AlSiN3:Eu0.01, only the oxidation of the host could be observed, which would lead to the luminescence degradation and even failure of these phosphors. The activator Eu2+ ions were much more stable in CaAlSiN3:Eu than Sr2Si5N8:Eu due to their crystal surroundings, and its concentration also influenced the temperature stability of Sr2Si5N8:Eu.