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

Abstract

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-NaGdF₄:Yb/Ho/Ce@β-NaYF₄:Tb/Eu core-shell structure have been skillfully designed and synthesized by a co-precipitation strategy. Through the cross-relaxation process between Ce³⁺ and Ho³⁺ 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 Ce³⁺ in the core. By selecting Ce³⁺ as the sensitizer for harvesting the energy of incident ultraviolet (UV) light and introducing Gd³⁺ 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 Gd³⁺-assisted interface energy transfer processes (Ce³⁺ → Gd³⁺ → Tb³⁺, Ce³⁺ → Gd³⁺ → Tb³⁺ → Eu³⁺). 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.