Oxidation and luminescence quenching of europium doped BaMgAl10O17 probed by HERFD-XANES

Eu-doped BaMgAl10O17 (BAM) is an excellent inorganic phosphor. Its luminescence efficiency is however severely degraded during prolonged vacuum-ultraviolet (VUV) excitation. Furthermore, the degradation process at the atomic level is not yet fully understood. To shed light on this process, we simultaneously employed X-rays as an equivalent but accelerated source of damage, as an excitation source of luminescence and as an element-selective probe of both dopants and host-lattice chemical species.
We investigated commercial samples of Eu doped and Mn, Eu co-doped BAM. We measured High-Energy Resolution Fluorescence Detected (HERFD)-XANES at Eu and Ba L3-edges and at Mn K-edge. The X-ray induced radio-luminescence (RL) and the HERFD-XANES spectra were simultaneously acquired while progressive damage was induced.
The evolution of the RL spectra confirms that the degradation induced by X-rays and by VUV irradiation are equivalent. The HERFD-XANES reveals that Ba and Mn are stable under the X-ray beam, while Eu2+ undergoes a rapid oxidation to Eu3+. We found that the correlation between Eu oxidation and RL intensity decay is non-linear and that a significant fraction of Eu2+ resists to irradiation, implying that an additional mechanism is responsible for the quenching of the remaining Eu2+. A kinetic Monte Carlo simulation indicates that the creation of defects acting as killer centers in the vicinity of a photo-oxidized Eu3+ can reproduce the dynamics observed on RL and Eu oxidation.
By simultaneously degrading and probing Eu-doped BAM we found [1] that the degradation process is due to oxidation of the luminescence impurities combined with the formation of killer centers that quench the luminescence of the remaining Eu2+.