Tm³⁺ mediated multicolor luminescence of NaYbF₄:Er,Tm@NaYF₄ for advanced anti-counterfeiting

Lanthanide doped multicolor luminescent materials have attracted extensive attention due to their advanced anti-counterfeiting properties. However, designing a simple, hard-to-copy and multicolor anti-counterfeiting strategy based on upconversion nanoparticles (UCNPs) remains a huge challenge. Herein, a strategy to modulate luminescence color by altering the mediating action of Tm³⁺ was proposed. As a proof of concept, the mediating action of Tm³⁺ was explored in NaYbF₄:30%Er,1%Tm@NaYF₄ by changing the doping ratio of Yb³⁺/Er³⁺/Tm³⁺, and red, yellow and blue luminescence was successfully obtained. Then, NaYbF₄:x%Er,1%Tm@NaYF₄ (x = 2, 10, 30, 50, 99), NaYbF₄:x%Er@NaYF₄ (x = 2, 10, 30, 50, 100) and NaYbF₄:1%Tm@NaYF₄:x%Er@NaYF₄ (x = 2, 10, 30, 50, 100) were synthesized to further identify that the mediating action of Tm³⁺ was related to the doping ratio and distance between dopant ions. In addition, the luminescence color of NaYbF₄:30%Er,1%Tm@NaYF₄ changed from red to yellow with the increase of excitation power density. Based on the above, NaYbF₄:Er,Tm@NaYF₄ UCNPs show excellent performance in anti-counterfeiting of paintings, thus revealing their great potential in advanced anti-counterfeiting applications.