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

Abstract

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.

High-Yb3+-Doped NaYbF4:10% Er@NaYF4 Alloyed Nanoparticles for Brightening Upconversion and Multi-Colorizing Information Encryption

“…As anticipated, CSS­(I) exhibited a quite low emission compared with CS (Figure a,b), which might be attributed to the Yb 3+ lattice inside the inner layer. The inside Yb 3+ can act as a medium that migrates excitation energy inside cores to crystal defects outsides (Figure c) . The emission of the second control CSS­(II) (NaYbF 4 :10% Er@NaYbF 4 @NaYF 4 :20% Yb) dropped dramatically.…”

“…The inside Yb 3+ can act as a medium that migrates excitation energy inside cores to crystal defects outsides (Figure 4c). 36 The emission of the second control CSS(II) (NaYbF 4 :10% Er@NaYbF 4 @ NaYF 4 :20% Yb) dropped dramatically. It is because its outer layer had Yb 3+ that dominated the energy loss, thereby mediating the migration of the excitation energy to the surface quenchers.…”

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

“…[4][5][6] Among them, lanthanide doped upconversion nanoparticles (UCNPs) show considerable competitiveness in the field of anti-counterfeiting due to their advantages of high light stability, adjustable emission color and low toxicity. [7][8][9][10][11] In order to improve the security of anti-counterfeiting, more and more researchers have focused on designing multi-color anti-counterfeiting strategies based on UCNPs. 12 The most common strategy is to synthesize multilayer core-shell UCNPs with orthogonal emission characteristics.…”

Controllable structural and optical properties of NaYF4:Tm, Yb microparticles by Yb3+ doping for anti-counterfeiting

“…This material exhibits outstanding applications such as photodetectors in NIR region, 10 photocatalyst, 11–13 biosensors, 14–16 and anti-counterfeit printing. 3,17 In addition, surface modification with various ligands has been used to improve the dispersibility and colloidal stability of NaYF 4 UCMPs and the conjugation of UCMPs with biomolecules, polymers, etc. 9,18–23 Thus, these modified UCMPs have more potential uses in fluorescent cell imaging, drug delivery, and optical temperature monitoring.…”

“…Studies on rare earth (RE)-doped upconversion (UC) phosphors have attracted the attention of researchers and developed rapidly owing to their abundant applications in solid-state lasers, three-dimensional at-panel displays, low-intensity infrared (IR) imaging, optical ber-based telecommunications, and especially anti-counterfeiting, bio-probes and bioimaging. [1][2][3][4] Compared with the traditionally used security ink and biological labels such as various organic dyes, metal complexes, and semiconductor quantum dots (QDs), RE-doped phosphor materials possess excellent luminescent characteristics consisting of abundant emissions ranging from visible to near IR, signicant Stokes shi, sharp emission peaks, and long uorescence lifetime, low toxicity, high thermal stability, long durability, and negligible photobleaching, etc. 4,5 Moreover, some UC phosphors have excitation and emission lights located within the NIR spectral range of 750-1000 nm (NIR-NIR UC emission), considered the "window of optical transparency" for biological tissues with a relatively high tissue penetration depth.…”