Efficient dual-mode luminescence from lanthanide-doped core-shell nanoarchitecture for anti-counterfeiting applications.

Fluorescent anti-counterfeiting technique is generally based on the development of luminescent materials, which generally exhibit single-mode emissions under single-wavelength excitation, thus resulting in a poor anti-fake effect. To improve the anti-forgery performance of fluorescent anti-counterfeiting approaches, dual-mode luminescent nanoparticles with the form of a β-NaGdF:Yb/Ho/Ce@β-NaYF:Tb/Eu core-shell structure have been skillfully designed and synthesized by a co-precipitation strategy. Through the cross-relaxation process between Ce and Ho ions in the inner core region, the up-conversion luminescence colors of the as-synthesized samples can be turned from green to yellow and finally to red when adjusting the dopant concentration of Ce in the core. By selecting Ce as the sensitizer for harvesting the energy of incident ultraviolet (UV) light and introducing Gd as the ideal intermediate for subsequent energy migration, the down-converting emission colors of the as-obtained samples are also regulated from green to red via a Gd-assisted interface energy transfer processes (Ce → Gd → Tb, Ce → Gd → Tb → Eu). Consequently, dual-mode luminescence with multi-color outputs can be achieved in the pre-designed core-shell nanostructure under the excitation of a 980 nm near-infrared laser and 254 nm UV light. The designed nanoarchitecture with bright dual-mode emissions and tunable colors greatly improves the ability of modern anti-counterfeiting, demonstrating its promising applications in anti-fake and optical multiplexing.