Study on the Luminescence Performance and Anti-Counterfeiting Application of Eu 2+ , Nd 3+ Co-Doped SrAl 2 O 4 Phosphor.

This manuscript describes the synthesis of green long afterglow nanophosphors SrAl 2 O 4 :Eu 2+ , Nd 3+ using the combustion process. The study encompassed the photoluminescence behavior, elemental composition, chemical valence, morphology, and phase purity of SrAl 2 O 4 :Eu 2+ , Nd 3+ nanoparticles. The results demonstrate that after introducing Eu 2+ 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 4f 6 5d 1 →4f 7 transition of Eu 2+ ions. The optimal doping concentrations of Eu 2+ and Nd 3+ 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 Eu 2+ and Nd 3+ . Then, we analyzed and compared the quantum yield, fluorescence lifetime, and afterglow decay time of the samples; the co-doped ion Nd 3+ 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 Eu 2+ , which gradually returns to the ground state after the excitation stops, generating an afterglow luminescence of about 15 s. The quantum yields of SrAl 2 O 4 :Eu 2+ and SrAl 2 O 4 :Eu 2+ , Nd 3+ phosphors were 41.59% and 10.10% and the fluorescence lifetimes were 404 ns and 76 ns, respectively. In addition, the E g value of 4.98 eV was determined based on the diffuse reflectance spectra of the material, which closely matches the calculated bandgap value of SrAl 2 O 4 . 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.