Eu²⁺-Activated Ba_0.5Sr_0.5Al₂O₄ Phosphors for Screen Printing and Anti-Counterfeiting Flexible Film

Herein, a series of Ba_0.5Sr_0.5Al₂O₄: xEu²⁺ (x = 0.01, 0.02, 0.03, 0.04, 0.06) nanophosphors were synthesized by a combustion method. The investigation encompassed the characterization of the phase purity, morphology, elemental composition, and photoluminescence behavior of Ba_0.5Sr_0.5Al₂O₄: xEu²⁺ nanoparticles. Under excitation by 303 nm and 365 nm ultraviolet light, the nanoparticles exhibited blue-green emission arising from the 4f⁶5d→4f⁷ transition of Eu²⁺ ions. The optimal doping concentration was determined to be 2%. Notably, the nanoparticles demonstrated fluorescence lifetimes and quantum yields of 1010 ns ((Formula presented.) _ex = 303 nm), 112 ns ((Formula presented.) _ex = 365 nm), 10.5%, and 10.3%, respectively. Additionally, a comprehensive analysis of the band structure and electronic density of states was conducted, revealing a theoretical direct band gap of 4.05 eV for the Ba_0.5Sr_0.5Al₂O₄ host. In addition, the prepared fluorescent powder can be used to prepare fluorescent flexible films. This film does not change the characteristic emission of Eu²⁺ ions and has more stable physicochemical properties, which may be more suitable for use in harsh environments. Also, the fluorescent powder can be blended with polyacrylic acid to form colorless anti-counterfeiting ink that can be applied to banknotes as an anti-counterfeiting mark. A clover pattern was successfully printed using screen-printing technology, proving its potential application in the field of anti-counterfeiting.