Study on the Luminescence Performance and Anti-Counterfeiting Application of Eu²⁺, Nd³⁺ Co-Doped SrAl₂O₄ Phosphor

Abstract

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl2O4:Eu2+, Nd3+ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl2O4:Eu2+, Nd3+ nanoparticles. The results demonstrate that after introducing Eu2+ into the matrix lattice, it exhibits an emission band centered at 508 nm when excited by 365 nm ultraviolet light, which is induced by the 4f65d1→4f7 transition of Eu2+ ions. The optimal doping concentrations of Eu2+ and Nd3+ were determined to be 2% and 1%, respectively. Based on X-ray diffraction (XRD) analysis, we have found that the physical phase was not altered by the doping of Eu2+ and Nd3+. Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd3+ itself does not emit light, but it can serve as an electron trap center to collect a portion of the electrons produced by the excitation of Eu2+, which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl2O4:Eu2+ and SrAl2O4:Eu2+, Nd3+ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the Eg value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl2O4. The material can be combined with polyacrylic acid to create optical anti-counterfeiting ink, and the butterfly and ladybug patterns were effectively printed through screen printing; this demonstrates the potential use of phosphor in the realm of anti-counterfeiting printing.

Keywords

• long afterglow
• SrAl₂O₄:Eu²⁺, Nd³⁺
• combustion method
• screen printing
• anti-counterfeiting