Effect of high-temperature annealing on the state of Eu$^{2+}$ ions in phosphors

The article considers the impact of high-temperature annealing in air upon optical and paramagnetic properties of the activator Eu$^{2+}$ ions in phosphors. The authors discovered that thermal stability of Eu$^{2+}$ ions located in two different crystallographic sites BaMg$_2$Al$_{16}$O$_{27}$ and (Sr,Ba)$_5$(PO$_4$)$_3$Cl is significantly different. The article shows a possibility of regulating the Eu$^{2+}$ concentration and phosphors spectral characteristics by means of high-temperature annealing.