Tm 3+ mediated multicolor luminescence of NaYbF 4 :Er,Tm@NaYF 4 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 3+ was proposed. As a proof of concept, the mediating action of Tm 3+ was explored in NaYbF 4 :30%Er,1%Tm@NaYF 4 by changing the doping ratio of Yb 3+ /Er 3+ /Tm 3+ , and red, yellow and blue luminescence was successfully obtained. Then, NaYbF 4 : x %Er,1%Tm@NaYF 4 ( x = 2, 10, 30, 50, 99), NaYbF 4 : x %Er@NaYF 4 ( x = 2, 10, 30, 50, 100) and NaYbF 4 :1%Tm@NaYF 4 : x %Er@NaYF 4 ( x = 2, 10, 30, 50, 100) were synthesized to further identify that the mediating action of Tm 3+ was related to the doping ratio and distance between dopant ions. In addition, the luminescence color of NaYbF 4 :30%Er,1%Tm@NaYF 4 changed from red to yellow with the increase of excitation power density. Based on the above, NaYbF 4 :Er,Tm@NaYF 4 UCNPs show excellent performance in anti-counterfeiting of paintings, thus revealing their great potential in advanced anti-counterfeiting applications.