Tm mediated multicolor luminescence of NaYbF:Er,Tm@NaYF 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 Tm was proposed. As a proof of concept, the mediating action of Tm was explored in NaYbF:30%Er,1%Tm@NaYF by changing the doping ratio of Yb/Er/Tm, and red, yellow and blue luminescence was successfully obtained. Then, NaYbF:%Er,1%Tm@NaYF ( = 2, 10, 30, 50, 99), NaYbF:%Er@NaYF ( = 2, 10, 30, 50, 100) and NaYbF:1%Tm@NaYF:%Er@NaYF ( = 2, 10, 30, 50, 100) were synthesized to further identify that the mediating action of Tm was related to the doping ratio and distance between dopant ions. In addition, the luminescence color of NaYbF:30%Er,1%Tm@NaYF changed from red to yellow with the increase of excitation power density. Based on the above, NaYbF:Er,Tm@NaYF UCNPs show excellent performance in anti-counterfeiting of paintings, thus revealing their great potential in advanced anti-counterfeiting applications.