Theoretical and Structural Study of Axial Symmetry Ce3+ Centers in the BaWO4 Single Crystal Doped with Cerium and Codoped with Sodium Ions

The spin-Hamiltonian parameters g-factors (g|| and g⟂) of the Ce³⁺ paramagnetic centers in BaWO₄: Ce and BaWO₄: Ce, Na single crystals with axial symmetry are investigated using the superposition model (SPM) via complete diagonalization procedure of energy matrix (CDM method). The calculated g-factors are in reasonable agreement with the experimental values. The fitted intrinsic parameters are comparable with data from other publications for rare-earth paramagnetic centers in a similar environment. The angular distortions of the cerium dodecahedron [CeO₈] are also studied. Structural analysis of paramagnetic centers with axial symmetry through the postulated cerium barium tetrahedron [CeBa₄] connected via oxygens bridges was carried out. The mechanism of the charge compensation and the role of the second dopant (Na⁺) is also discussed.

Structure and Photoluminescence Properties of Rare-Earth (Dy3+, Tb3+, Sm3+)-Doped BaWO4 Phosphors Synthesized via Co-Precipitation for Anti-Counterfeiting

Barium tungstate (BaWO₄) powders with various sintering temperatures, and BaWO₄:Dy³⁺ phosphor samples with concentrations of different rare-earth (RE) activator ions (Dy³⁺, Sm³⁺, Tb³⁺) were prepared through co-precipitation. The structural, morphological, and photoluminescent characteristics of barium tungstate phosphors depend on the concentration of RE ions. The crystallographic characteristics of the synthesized BaWO₄ were analyzed using X-ray diffraction (XRD) patterns. The size and shape of the crystalline particles were estimated based on images measured with a field emission scanning electron microscope (FE-SEM). As the sintering temperature of the BaWO₄ particles increased from 400 °C to 1000 °C, the size of the particles gradually increased and showed a tendency to clump together. In the sample doped with 7 mol % Dy³⁺ ions, the intensity of all emission bands reached their maximum. The emission spectra of the RE³⁺-doped BaWO₄ powders by excitation at 325 nm were composed of yellow (Dy³⁺), red (Sm³+), and green (Tb³⁺) band at 572, 640, and 544 nm. This indicates that most of the RE³⁺ ions absorbed the position without reversal symmetry in the BaWO₄ lattice. These results propose that strong emission intensity and tunable color for the phosphors can be accomplished by rare-earth doped host with an suitable quantity. In addition, the phosphor thin films, having high transparency from aqueous colloidal solutions, were deposited on banknotes, and it is considered whether it is suitable for anti-counterfeiting applications.