Dual-wavelength stimuli and green emission response in lanthanide doped nanoparticles for anti-counterfeiting

Lanthanide doped nanoparticles play an important role in the applications of anti-counterfeiting due to their outstanding optical properties, including large Stokes shift, high color purity, long lifetimes, and excellent photostability. However, the excitation wavelength of most luminescent lanthanide doped materials is strictly limited to a small range owing to the narrow absorption band of doped lanthanide ions. Herein, NaYbF4:Tb@NaGdF4:Ce core-shell nanoparticle was developed and synthesized by high temperature coprecipitation method. The core-shell nanoparticles exhibited green emission of doped Tb3+ ions under the excitation of 980 nm in the near-infrared (NIR) region or 254 nm in the ultraviolet (UV) region, respectively. The NIR excitation was realized through cooperative sensitization upconversion process from Yb3+ to Tb3+ in the core, while the UV excitation was achieved by energy transfer from Ce3+ to Gd3+ and to Tb3+ across the interfaces. The two-mode of excitation increased the security level of information coding and improved the reliability of anti-counterfeiting. Significantly, the interference of background fluorescence can be overcome by choosing the appropriate excitation wavelength. As a proof of concept, the core-shell nanoparticles for anti-counterfeiting applications were demonstrated.