Multi-color photoluminescence and persistent luminescence of Eu³⁺-doped Zn2GeO4 for security applications

초록

While Eu-3 (+)-doped phosphors have been extensively studied for optical applications, many studies have primarily focused on activator emissions with limited attention to the combined effects of host defect emissions and persistent luminescence (PersL). We investigated the luminescence properties of Eu3+-doped Zn2GeO4 (ZGO:Eu) and its potential applications in optical anti-counterfeiting and encryption technologies. Samples were synthesized via a solid-state reaction with Eu3+ doping concentrations of 0.00, 0.005, 0.01, 0.02, and 0.04. An X-ray diffraction (XRD) analysis and Rietveld refinement confirmed that the rhombohedral phase and lattice parameters of ZGO:Eu remained unchanged across the doping concentrations. Photoluminescence studies revealed green emission under ultraviolet (UV) irradiation at 270 nm, which was attributed to host defects, along with red emission under UV irradiation at 394 nm, which resulted from the 4f-4f transitions of Eu3+ ions. When we measured the quantum yield (QY) of ZGO:Eu under 270 nm and 394 nm excitation, it recorded 19 and 31 %, respectively. In addition, the PL intensity remained above 40 % even in a high-temperature environment. Measurements showed that the duration of the PersL depended on the Eu3+ concentration, reaching a maximum green PersL of similar to 15 s when the concentration was 0.01. Based on these findings, we created a hidden pattern to demonstrate its potential for optical anti-counterfeiting and encryption applications. These results demonstrate that ZGO:Eu offers a multifunctional platform combining multi-color photoluminescence and time-dependent optical features, showing strong potential for advanced anti-counterfeiting and optical encryption applications.

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