Visualizing the valence states of europium ions in Eu-doped BaAl₂O₄ using X-ray nanoprobe mapping

This study develops and successfully demonstrates visualization methods for the characterization of europium (Eu)-doped BaAl₂O₄ phosphors using X-ray nanoprobe techniques. X-ray fluorescence (XRF) mapping not only gives information on the elemental distributions but also clearly reveals the valence state distributions of the Eu²⁺ and Eu³⁺ ions. The accuracy of the estimated valence state distributions was examined by performing X-ray absorption spectroscopy (XAS) across the Eu L₃-edge (6.977 keV). The X-ray excited optical luminescence (XEOL) spectra exhibit different emission lines in the selected local areas. Their corresponding emission distributions can be obtained via XEOL mapping. The emission properties can be understood through correlation analysis. The results demonstrate that the main contribution to the luminescence intensity of the Eu-doped BaAl₂O₄ comes from the Eu²⁺ activator and the emission intensity will not be influenced by the concentration of Eu²⁺ or Eu³⁺ ions. It is anticipated that X-ray nanoprobes will open new avenues with significant characterization ability for unravelling the emission mechanisms of phosphor materials.