NaYF₄:Yb,Er@NaYF₄:Yb,Tm and NaYF₄:Yb,Tm@NaYF₄:Yb,Er Core@Shell Upconversion Nanoparticles Embedded in Acrylamide Hydrogels for Anti-Counterfeiting and Information Encryption

Multicolor upconversion luminescence (UCL) plays an essential role in anti-fake and information encipher. Here, we report a strategy to expand the color-adjustable emission range by regulating the doping concentration of Yb³⁺ in core@shell (C@S) upconversion nanoparticles (UCNPs) under the excitation of near-infrared (NIR) light at 980 nm and promoting the energy-transfer process. Subsequently, multicolor UCNPs were combined with acrylamide hydrogel to construct a three-dimensional (3D) information code with an adjustable emission color. The encoded information is readable only under 980 nm excitation light and disappears as soon as the excitation light is removed. We adopted three strategies to improve the security: multiple permutations and combinations of different emission light hydrogel blocks, the combination of rich optical information and binary code, and the shape coding of hydrogel blocks. Constructing a complex and changeable coding library significantly guarantees that the data can be enciphered and deciphered by simple light irradiation, and the content can be edited by permutation and combination combined with information coding rules. Therefore, it is expected to provide ideas for developing intelligent anti-counterfeiting materials and devices.