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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. [ABSTRACT FROM AUTHOR]

Herein, a series of novel long afterglow nanophosphors BaYAl3O7:Eu2+, Nd3+ was synthesized by the combustion method. The investigation encompassed the characterization of X-ray diffraction, morphology, chemical valence, elemental composition, and photoluminescence behavior of BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ nanoparticles. Under 365 nm excitation, BaYAl3O7:Eu2+ and BaYAl3O7:Eu2+, Nd3+ show emission bands centered at 497 nm and 492 nm, which are attributed to the 4f65d→4f7 transition of Eu2+ ions. The optimal samples of BaYAl3O7:0.03Eu2+ and BaYAl3O7:0.03Eu2+, 0.02Nd3+ have average fluorescence lifetimes of 850 ns and 1149 ns, respectively. The co-doping of Nd3+ ions as the trap centers produced long afterglow luminescence properties, and the afterglow time could reach up to 8 min. Furthermore, the fluorescent powder can be mixed with polyacrylic acid to prepare anti-counterfeiting inks; a clover pattern and snowflake pattern have been successfully printed using screen printing technology, proving its potential application in the field of anti-counterfeiting. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Herein, a series of Ba0.5Sr0.5Al2O4: 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 Ba0.5Sr0.5Al2O4: 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 (λ ex = 303 nm), 112 ns (λ 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 Ba0.5Sr0.5Al2O4 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. [ABSTRACT FROM AUTHOR]

Green emitting long afterglow phosphor SrAl2O4: Eu2+, Dy3+ was synthesized via the combustion method. The physical phase analysis was carried out by X-ray diffraction, the results show that the introduction of Eu2+ into the lattice of the matrix resulted in a broad green emission centered at 508 nm, which is ascribed to the characteristic 4f65d1 to 4f7 electronic dipole allowed transition of Eu2+ ions. The doping of Eu2+ and Dy3+ did not change the physical phase of the crystals. Dy3+, as a coactivator, does not emit light itself, but can generate holes to form a trap energy level, which acts as an electron trap center to capture some of the electrons generated by the excitation of Eu2+. After excitation has ceased, let them gradually to transfer to the ground state for long afterglow luminescence. Then, we investigate the optical characterizations of different samples excited by X-ray. We found that SrAl2O4: Eu2+, 0.5% Dy3+ has this higher luminous intensity and afterglow. Its fluorescence lifetime is about 720 ns, and its quantum yield can reach 15.18%. Through search engine marketing (SEM) and energy dispersive X-ray spectroscopy (EDX), it has been proved that the sample has been successfully synthesized and its component content has been confirmed. The Eg value calculated from the diffuse reflectance spectrum is 4.61eV. The prepared SrAl2O4: Eu2+, Dy3+ luminescent powder is combined with Polydimethylsiloxane substrate for anticounterfeiting application, which provides a novel idea and method for the development of the anticounterfeiting field. [ABSTRACT FROM AUTHOR]