Insights of Peculiar Green-Yellow Emission Occurrence in Ce³⁺-Doped Barium Yttrium Orthogermanate Phosphors

Abstract

orthogermanate phosphor, prepared by LiCl flux assistance under a reducing atmosphere, exhibited a mysterious green-yellow emission at 298 K. A blue-emitting orthogermanate phosphor was expected to be achieved through the lower d-band of Ce 3+ ions in the host structure owing to their optical structure geometry. Oxygen vacancies were observed in the phosphors through investigating bond-length fluxations, the oxygen 1s profile, and the Ge 2+ /Ge 4+ oxidation state, using synchrotron X-ray diffraction refinement, X-ray photoelectron spectroscopy, and Ge K-edge X-ray absorption near-edge structure spectra, respectively. The Ba-M 4,5 edge shift, bonding limitation, and distortion index discovery reveal the oxygencoordinating environment variation around the Ba 2+ (Ce 3+ ) ions in the phosphors. The green-yellow emission results from the active 6-coordinated antiprism oxygen geometry around the Ce 3+ ions in the phosphors.

Multiband MgGeO3-Based Persistent Luminescent Nanophosphors for Dynamic and Multimodal Anticounterfeiting

“…Therefore, the Ge K-edge XAFS was measured to compare the bonding environments of the two MGO:Mn. The Ge K-edge XANES has a strong whiteline (WL) feature (1s → 4p) that appears at ∼11110 eV indicating Ge in both sol–gel and hydrothermally synthesized MGO has an oxidation state of +4. , The WL of MGO:Mn-sg is higher and broader than that of MGO:Mn-h, as shown in Figure e, indicating that there are more unoccupied electrons in the Ge 4p level, as the WL intensity is strongly related to the electronic density of the unoccupied state in the conduction band. The Ge K-edge EXAFS spectra in the R space with the first-shell fit are plotted in Figure f (the k space plots can be found in Support Information, Figure S8).…”