Designing Tb3+-Sensitized Silica-Nanoparticles-Aided Eu3+-Doped Sr2SiO4 Phosphors with Enhanced Luminescence for Anti-Counterfeiting Applications

Silica-nanoparticles-assisted Eu³⁺-doped Sr₂SiO₄ and Tb³⁺- and Eu³⁺-co-doped Sr₂SiO₄ phosphors, as potential phosphors for anti-counterfeiting application are synthesized via a solid-state reaction technique. The crystal structure, photoluminescence, and decay times are investigated. The characteristic emission of Eu³⁺-doped Sr₂SiO₄ phosphors exhibits two major peaks at 617 and 595 nm under an excitation wavelength of 394 nm, which corresponds to ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₁ electron transitions of Eu³⁺ ions. Upon co-doping with Tb³⁺, the red emission intensities of the Eu³⁺-doped Sr₂SiO₄ phosphors are enhanced by 1.78-fold times through an energy-transfer process. The optimized Tb³⁺- and Eu³⁺-co-doped Sr₂SiO₄ phosphors show a decay time of 0.49 ns and an energy-transfer efficiency of 73%. The calculated International Commission on Illumination value (x, y) and color purity are (0.63, 0.37) and 94%, respectively. Subsequently, a luminescent ink is formulated using the optimized phosphor and tested for efficiency on currency notes. Additionally, a flexible film is fabricated, and its luminescence properties are studied. The formulated ink can serve as security ink in the anti-counterfeiting application.