Determination of Eu Sites in Highly Europium-Doped Strontium Aluminate Phosphor Using Synchrotron X-Ray Powder Diffraction Analysis

Abstract

Highly europium-doped strontium aluminate phosphor particles were prepared by microspray pyrolysis. The crystallographic sites of the doped ions and their local atomic coordinates were determined using a combination of Rietveld refinement and the maximum entropy method (MEM) with high-resolution synchrotron X-ray powder diffraction data. The final Rietveld refinement yielded good factors of and with the following lattice parameters: , , , and . It was evident that there were two crystallographic sites for doped ions, namely, Eu1 and Eu2, which were located far from the Sr sites and had displacements of 0.200(7) and , respectively. Comparison of the resulting local atomic coordinates of Eu1 and Eu2 revealed similar atomic configurations at both Eu sites, indicating that the emission peaks for both appeared at almost the same positions. Electron density distribution was calculated by MEM, and the results clearly showed that all the doped ions were introduced near Sr1 and Sr2; no other possible crystallographic sites were found. In addition, a subtle electron density between and ions was observed, implying the occurrence of charge transfer between and ions.