Achieving tunable photoluminescence emission in CaCdGe7O16:Sm3+ persistent luminescence phosphors for optical anti-counterfeiting

Abstract

Persistent luminescence phosphors have attracted much attention in the realm of anti-counterfeiting and information storage because of their characteristic properties of optical information storage, long persistent luminescence, and simplicity of design. At present, traditional anti-counterfeiting persistent luminescence phosphors are based on single-colour luminescence and generally have poorly secure anti-counterfeiting capabilities. In this work, Ca_1−1/2xCd_1−1/2xGe₇O₁₆:xSm³⁺ (x = 0, 0.0025, 0.005, 0.01, 0.015, 0.02, and 0.025) phosphors were synthesized using a high-temperature solid-state reaction method, which demonstrated potential as multi-colour and two-mode anti-counterfeiting persistent luminescence materials. With an increase in doping concentration of Sm³⁺ ions in the host, the materials could emit blue-to-pink photoluminescence under 254 nm UV lamp illumination. After excitation under a 254 nm UV lamp, the materials showed persistent luminescence performance with a pink persistent luminescence colour, and the duration could exceed 4 h. The persistent luminescence mechanism and electron traps inside the samples were analyzed by plotting their thermoluminescence curves after excitation cessation. The results show that at least two types of traps existed in the Ca_1−1/2xCd_1−1/2xGe₇O₁₆:0.01Sm³⁺ phosphor. The phosphors were used to synthesize anti-counterfeiting ink, which was then used to make an optical anti-counterfeiting pattern through screen printing. The pattern could barely be observed on white paper in sunlight but was visible in different colours under an irradiation of 254 nm and in a low light environment. The results show that the produced phosphors have a high level of application potential for use in enhanced optical anti-counterfeiting applications.