Study on the Structure-Luminescence Relationship and Anti-Counterfeiting Application of (Ca,Sr)-Al-O Composite Fluorescent Materials.

A novel long-lasting luminescent composite material based on the (Ca,Sr)-Al-O system was synthesized using a solution combustion method. (Ca,Sr)3Al2O6 is the primary phase, with SrAl2O4 as a controllable secondary phase. Compared to conventional single-phase SrAl2O4 phosphors, the introduction of a calcium-rich hexaaluminate matrix creates additional defects and a specific trap distribution at the composite interface, significantly improving carrier storage and release efficiency. Eu2+ + Nd3+ synergistic doping enables precise control of the trap depth and number. Under 365 nm excitation, Eu2+ emission is located at ~515 nm, with Nd3+ acting as an effective trap center. Under optimal firing conditions at 700 °C (Eu2+ = 0.02, Nd3+ = 0.003), the afterglow lifetime exceeds 30 s. Furthermore, The (Ca,Sr)3Al2O6 host stabilizes the lattice and optimizes defect states, while synergizing with the SrAl2O4 secondary phase to improve the afterglow performance. This composite phosphor exhibits excellent dual-mode anti-counterfeiting properties: long-lasting green emission under 365 nm excitation and transient blue-violet emission under 254 nm excitation. Based on this, a screen-printing ink was prepared using the phosphor and ethanol + PVB, enabling high-resolution QR code printing. Pattern recognition and code verification can be performed both in the UV on and off states, demonstrating its great potential in high-security anti-counterfeiting applications. Compared to traditional single-phase SrAl2O4 systems, this study for the first time constructed a composite trap engineering of the (Ca,Sr)3Al2O6 primary phase and the SrAl2O4 secondary phase, achieving the integration of dual-mode anti-counterfeiting functionality with a high-resolution QR code fluorescent ink.