![]() According to Vegard’s law, a complete solid solution should form if the size difference of ions is in the range of ☑5% 25. ![]() This result can be extended to the other Ba 2+ ions. For the Ba atom sites, such as the 12-fold coordination Ba(3) site, Bi 3+ (r = 1.45 Å) and Eu 3+ (r = 1.23 Å) ions are smaller than Ba 2+ (r = 1.61 Å) ions, and therefore, the Bi 3+ and Eu 3+ ions are expected to randomly substitute the Ba 2+ sites. For easy distinguish, we can define the three distinct types of Ba sites and one Lu site as Ba(1), Ba(2), Ba(3) and Lu, respectively, and all these sites can be substituted by Bi 3+ or Eu 3+ ions. While the Ba 2+ ions are designated in three independent sites: Ba(1) at the 3 a Wyckoff position with 12-fold coordination, Ba(2) at the 6 c Wyckoff position with 9-fold coordination and Ba(3) at the 18 f Wyckoff position with 10-fold coordination, forming three different distorted polyhedra with different Ba-O bond lengths. In the crystal structure, the Lu 3+ ions are located at the 6 c Wyckoff position with 6-fold coordination, evolving a distorted LuO 6 octahedron that has two different Lu-O bond lengths 20. It exhibits the layered distribution in which the smaller tetrahedral SiO 4 units and the larger octahedral LuO 6 units are corner-shared as SiO 4-LuO 6-SiO 4-LuO 6, forming a rigid three-dimensional network 7. ![]() The crystal structure of the BLSO unit cell viewed from the a-axis and the c-axis is shown in Fig. The energy transfer mechanism from Bi 3+ to Eu 3+ was confirmed via an electric dipole-dipole interaction, the energy transfer efficiencies \((\) (148) space group 20. Interestingly, the as-prepared phosphor could generate warm white light/tunable emission by changing the concentration of Eu 3+ ions or adjusting the excitation wavelength. Moreover, due to the complex energy transfer processes among these Bi 3+ centers, their relative emission intensity tightly depended on the incident excitation wavelength. From the analyses of the crystal structure and luminescent spectra, we observed four discernible Bi 3+ luminescent centers with peaks at ~363.3, ~403.1, ~437.7, and ~494.5 nm. X-ray diffraction, crystal structure analysis, diffuse reflectance and luminescent spectra, quantum efficiency measurements, and thermal stability analysis were applied to investigate the phase, structure, luminescent and thermal stability properties. A Bi 3+ and Eu 3+ ion co-doped Ba 9Lu 2Si 6O 24 single-phased phosphor was synthesized successfully via a conventional high-temperature solid-state reaction.
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