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 Sr_1.98-x-y-zCa_yBa_zMgSi₂O₇:0.02Dy³⁺,xEu²⁺ (abbreviated as SC_yB_zMS: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.