Chemistry of Materials (2017)

Oxidation and Luminescence Quenching of Europium in BaMgAl10O17 Blue Phosphors
Lucia Amidani, Katleen Korthout, Jonas J. Joos, Marte van der Linden, Heleen F. Sijbom, Andries Meijerink, Dirk Poelman, Philippe F. Smet, Pieter Glatzel
Chemistry of Materials 29 (2017) 10122-10129

Abstract
The efficient blue luminescence of Eu2+ doped BaMgAl10O17 is well-known to be severely degraded by prolonged irradiation with vacuum-ultraviolet light. The degradation process at the atomic level is however not fully understood. In this work we employed X-rays as an equivalent but accelerated cause of degradation, as an excitation source of luminescence and as an element-selective probe of both dopants and host-lattice chemical species. The X-ray absorption near edge structure (XANES) recorded in high energy resolution mode reveals that the structural properties of the host lattice are preserved during irradiation, while Eu2+ is rapidly oxidized. The correlation between Eu oxidation as derived from XANES and the decrease of blue luminescence is however not linear and a significant fraction of Eu2+ survives degradation, implying additional mechanisms for the quenching of the luminescence. Defects created during the photogeneration may reduce the ability of the remaining Eu2+ to receive or to radiatively release energy. A kinetic Monte Carlo simulation confirms that defects in the vicinity of a photogenerated Eu3+ can act as killer centers for the remaining Eu2+ and explain the observed accelerated quenching of the blue luminescence. The present approach, which takes full advantage of the different interactions of X-ray radiation with impurity doped luminescent materials, can easily be transferred to reveal degradation pathways in other phosphors.

Keywords: BAM:Eu; XANES; degradation; Monte Carlo

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