Multi-mode anti-counterfeiting guarantees from a single material CaCd2Ga2Ge3O12:Tb3+,Yb3+ – two stimuli-responsive and four-state emission

Abstract

Luminescent anti-counterfeiting materials have drawn much attention in anti-counterfeiting applications due to their photochemical stability and emission patterns. However, conventional materials majorly use single-mode luminescence, leaving a growing demand for new materials to prevent counterfeiting. In this work, multi-mode anti-counterfeiting is guaranteed from a single luminescent material CaCd₂Ga₂Ge₃O₁₂:Tb³⁺,Yb³⁺via a high-temperature solid-state reaction. The experimental result showed that this single material features green luminescence with excellent photoluminescence, afterglow, thermoluminescence, and up-conversion luminescence, which are ascribed to Tb³⁺ transitions. Upon co-doping with Yb³⁺ as a sensitiser, the photo-stimuli responsiveness was achieved at 254 and 980 nm excitation sources, respectively, and the thermo-stimuli responsiveness was realised after exposure to UV of 254 nm for 10 s and heating at 45 °C, respectively. The band structure calculation, trap distribution, and effective trap depths were used to explain the luminescence mechanism. Based on the two-stimuli responsiveness and four-state emission performance, we prepared images of optical devices using silk screen printing technology. It was found that the images displayed green emission under different luminescence modes. The results prove that we successfully constructed an advanced luminescence anti-counterfeiting material.