Unleashing the Potential of Defect Engineered Persistent Pr3+-Activated Phosphors for Multi-Dimensional Anti-Counterfeiting and X-Ray Imaging Applications

Abstract

Persistent luminescence (PersL) in inorganic phosphors offers great potential for anti-counterfeiting and optical storage, with optimization of PersL, multicolor tuning, and defect engineering. This study presents a Ca₃Ga₂Ge₃O_12:Pr³⁺ (CGGO:Pr) phosphor with long-lasting PersL and multicolor emissions. Aliovalent codoping with Er³⁺ and Yb³⁺ ions optimizes deep/shallow trap redistribution, controlling trap depths from 0.98 to optimal 0.73 eV through the creation of new shallow electron traps (Yb_Ca^•, Er_Ca^•) alongside existing V_O levels. The smart Pr³⁺/Er³⁺/Yb³⁺:CGGO phosphor exhibits three-dimensional visible emissions under 275 and 380 nm excitation, as well as upconversion emissions under 980 nm laser irradiation. Hybrid density functional calculations, thermoluminescence, and positron annihilation lifetime spectroscopy revealed the nature and density of different traps controlling the PersL. Together, a single system featuring multicolor luminescence has been developed, exhibiting improved PersL and regulated trap depths (≈0.73 eV) suitable for robust and multimodal anti-counterfeiting of documents, pharmaceuticals, and industrial products. Furthermore, the composite PMMA-CGGO:Pr phosphor films have shown remarkable capability for X-ray imaging, achieving a resolution of 4 lp/mm, which exceeds that of commercial Gd₂O₂S:Tb screens. These findings highlight the potential of this work for advanced anti-counterfeiting and X-ray imaging applications, offering enhanced PersL with controlled trap depths.