Cation substitution engineering persistent luminescence for dynamic optical anti-counterfeiting.

Long-persistent phosphors possess the unique ability to emit light long after excitation ceases. However, the tunable luminescence with diverse emission colors remains critically needed for applications such as advanced optical anti-counterfeiting. Herein, we designed a series of Sr1.98-x-y-zCayBazMgSi2O7:0.02Dy3+,xEu2+ (abbreviated as SCyBzMS:0.02Dy3+,xEu2+, 0 ≤ x ≤ 0.04, 0 ≤ y ≤ 2, and 0 ≤ z ≤ 1) phosphors using cation substitution engineering. XRD analysis confirmed the single-phase structure. The phosphors exhibit intense broad excitation bands spanning 250-450 nm. In the initial Sr2MgSi2O7 (SMS) host, Eu2+ produces a blue emission band centered at 470 nm, with an optimal doping concentration of x = 0.005. Substituting Sr2+ with Ca2+ and Ba2+ shifts the Eu2+ emission band toward longer and shorter wavelengths, respectively, accompanied by doping-content-dependent luminescence enhancement. The variations in emission colors primarily result from modification of the crystal fields surrounding the Eu2+ luminescent centers. Consequently, the emission colors are continuously tuned from blue to yellow. All the synthesized samples show long afterglow durations, and thermoluminescence curves elucidate the trap mechanism. Leveraging these spectral characteristics, we developed flexible optical anti-counterfeiting devices. Dynamic luminescent patterns enabled by long-afterglow emission demonstrate the enhanced anti-counterfeiting performance.