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

Yu-Hao Wu,Yung-Yang Lin,Bi-Hsuan Lin,Shu-Chi Huang,Chien-Yu Lee,Bo-Yi Chen,Gung-Chian Yin,Jeng-Lung Chen,E-Wen Huang,Shih-Yu Fu,Mau-Tsu Tang

doi:10.1107/s1600577521012947

Abstract

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.

Highlights

Phosphor-converted white-light-emitting diodes have been studied widely to develop more stable and efficient wLEDs (Xia et al, 2019)
Using an X-ray nanoprobe, X-ray fluorescence (XRF) and X-ray excited optical luminescence (XEOL) mapping can clearly reveal the distributions of the constituent elements, the valence states of the Eu2+ and Eu3+ ions, and the different emission wavelengths
The X-ray absorption spectroscopy (XAS), XRF and XEOL experiments were conducted on the Taiwan Photon Source (TPS) 23A X-ray nanoprobe beamline located at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan

Summary

Introduction

Phosphor-converted white-light-emitting diodes (wLEDs) have been studied widely to develop more stable and efficient wLEDs (Xia et al, 2019). The valence states of the rare earth ions significantly affect the emission properties of the phosphors. By exploiting the advantages of X-ray nanoprobes, including the continuously tunable X-ray energy (4–15 keV) and excellent spatial resolution of the nano-focused X-ray beam (

Results

Experiment

Conclusions