Energy Manipulation in Lanthanide-Doped Core–Shell Nanoparticles for Tunable Dual-Mode Luminescence toward Advanced Anti-Counterfeiting

Developing advanced luminescent materials and techniques is of significant importance for anti-counterfeiting applications, and remains a huge challenge. In this work, a new and efficient approach for achieving efficient dual-mode luminescence with tunable color outputs via Gd³⁺-mediated interfacial energy transfer, Ce³⁺-assisted cross-relaxation, and core–shell nanostructuring strategy is reported. The introduction of Ce³⁺ into the inner core not only serves the regulation of upconversion emission, but also facilitates the ultraviolet photon harvesting and subsequent energy transfer to downshifting (DS) activators in the outer shell layer. Furthermore, the construction of the core@shell nanoarchitecture enables the spatial separation of upconverting activators and DS centers, which greatly suppresses their adverse cross-relaxation processes. Consequently, efficient and multicolor-tunable dual-mode emissions can be simultaneously observed in the pre-designed NaGdF₄:Yb/Ho/Ce@NaYF₄:X (X = Eu, Tb, Sm, Dy) core–shell nanostructures under 254 nm ultraviolet light and 980 nm laser excitation. The proof-of-concept experiment demonstrates that 2D-encoded patterns based on dual-mode emitting nanomaterials are very promising for anti-counterfeiting applications. It is believed that this preliminary study will advance the development of the fluorescent materials for potential applications in anti-counterfeiting and optical multiplexing.