Theoretical Investigation of Intercalated Water Molecules and Hydroxyl Groups in BAM ( BaMgAl10O17 : Eu2 + ) Phosphor and Associated Degradation Processes

Abstract

Intercalation of water molecules into the β-alumina lattice of barium magnesium aluminate has been recently reported to be responsible for degradation of this phosphor. The associated degradation process is characterized by a green shift of the emission spectrum accompanied by oxidation of the activator ions. However, the structure and location of intercalated water molecules, and the degradation mechanism are not understood. In this report, both the location and geometry of water molecules are investigated using an atomistic simulation method with empirical interatomic potentials and a quantum mechanical method of structure optimization using full periodicity of the lattice. The oxidation of activator ions is modeled based on dissociation of water molecules to hydroxyl groups in this lattice. It is shown that the dissociation to hydroxyl groups is energetically favorable, and that the protons released in the process could be responsible for oxidation of europium ions.