A series of long-afterglow luminescent materials (SrAl2O4: Eu2+ (SAOE), SrAl2O4: Eu2+, Dy3+ (SAOED) and SrAl2O4: Eu2+, Dy3+, Gd3+ (SAOEDG)) was synthesized via the combustion method. Temperature and concentration control experiments were conducted on these materials to determine the optimal reaction temperature and ion doping concentration for each sample. The crystal structure and luminescent properties were analyzed via X-ray diffraction (XRD), photoluminescence (PL), and afterglow attenuation curves. The outcomes demonstrate that the kind of crystal structure and the location of the emission peak were unaffected by the addition of ions. The addition of Eu2+ to the matrix's lattice caused a broad green emission with a central wavelength of 508 nm, which was attributed to the characteristic 4f65d1 to 4f7 electronic dipole, which allowed the transition of Eu2+ ions. While acting as sensitizers, Dy3+ and Gd3+ could produce holes to create a trap energy level, which served as an electron trap center to catch some of the electrons produced by the excitation of Eu2+ but did not itself emit light. After excitation ceased, this allowed them to gently transition to the ground state to produce long-afterglow luminescence. It was observed that with the addition of sensitizer ions, the luminous intensity of the sample increased, and the afterglow duration lengthened. The elemental structure and valence states of the doped ions were determined with an X-ray photoelectron spectrometer (XPS). Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the samples. The results show that the sample was synthesized successfully, and the type and content of ions in the fluorescent powder could be determined. The fluorescence lifetime, quantum yield, bandgap value, afterglow decay time, and coordinate position in the coherent infrared energy (CIE) diagram of the three best sample groups were then analyzed and compared. Combining the prepared phosphor with ink provides a new idea and method for the field of anti-counterfeiting through screen printing.
Keywords: Eu2+, Dy3+, Gd3+; SrAl2O4; anti-counterfeiting; bandgap; long afterglow; mechanism of afterglow; rare-earth elements.