Distinctive occurrences of green-yellow luminescence from orthogermanate-type Ba9Y2(GeO4)6:Ce3+, Na+ phosphors under blue excitation and white-light performance with light-emitting diodes

• DOI: 10.1016/j.jallcom.2021.163213
• Publication Date: 2021-12-10T11:37:00Z
• Authors: Seungyong Shin; Sungjun Yang; Seong-hun Lee; Tae Joo Shin; Sangmoon Park
• Keywords: 02 engineering and technology; 0210 nano-technology; 530; 01 natural sciences; 0104 chemical sciences

In this study, barium yttrium orthogermanate luminescent host was prepared by a solid-state method using LiCl flux and combined with Ce3+-doped phosphor-converted light-emitting diodes (pc-LEDs) under blue excitation. The structure of Ba9Y2(GeO4)(6) (Ba9Y2Ge6O24) was determined with the use of synchrotron X-ray powder diffraction. The compound crystallized in trigonal unit cell (R (3) over barH), which contains 12-, 9-, and 10-coordinated Ba sites with isolated tetrahedral Ge-O4 and octahedral Y-O6 polyhedrons. The X-ray diffraction patterns, photoluminescence spectra, defect characterization results, Gaussian deconvolution of fitting emission bands, ligand-field splitting parameters, D-band edge positions, distortion values, cation occupancy results, and scanning electron microscopy images of the Ce3+-doped phosphors were characterized to figure out the specific origin of the green-yellow luminescence under blue excitation. The white emission spectra, color-rendering index, correlated color temperature, Commission Internationale de l'Eclairage coordinates and internal quantum efficiency of Ba8.8Ce0.1Na0.1Y2Ge6O24 phosphors on a blue LED chip were measured. Finally, the valence states of Gel' ions in the Ba8.8Ce0.1Na0.1Y2Ge6O24 phosphors were determined by the extended X-ray absorption fine structure analysis at the Ge K-edge to elucidate the luminescence loss under a strong reduction atmosphere. (C) 2021 Elsevier B.V. All rights reserved.