Hierarchical Disordered Colloidal Thin Films with Duplex Optical Elements for Advanced Anti‐Counterfeiting Coding

Abstract

Multiscale structures are found in nature to impart brilliant structural colors with integrated properties of multiple optical elements. However, it remains challenging to build more than one optical element into artificial photonic materials in practical manufacturing. Here, hierarchical disordered photonic superstructures (HDPSs) with optical properties arising from tailored interplay of thin‐film interference (TFI) and coherent scattering from amorphous colloidal arrays (ACAs) are fabricated through the combined use of infiltration‐driven colloidal assembly and micro‐imprinting. Uniform thin ACA films with TFI effects (ACA‐TFIs) are first coated on premium glossy photo papers, displaying near‐isotropic colors under natural light and mixed colors upon specular lighting due to the duplex optical effects. Such collective effects are easily modulated by the film thicknesses of ACA‐TFIs. Also, micro‐imprinting that can remove a patterned monolayer of particles from ACA‐TFI films causes suppressed TFI in the imprinted regions, leading to HDPS films with encoded optical features. Collectively, HDPS anti‐counterfeiting labels with covert and sophisticated optical coding are achieved and their enhanced complexity results in infinite possible optical features that are virtually impractical to forge, opening new avenues to high‐level security applications.

Self-assembly of colloidal particles into amorphous photonic crystals

“…Duan and co-workers fabricated the thin-film APCs which were assembled by spherical/polyhedral metal-organic framework (MOF) colloidal particles. 101,102 Similarly, Chen et al reported a crack-free, arbitrarily bendable film of APCs with bright structural color prepared by vacuum filtration of colloidal suspension through an reduced graphene oxide-sulfopropyl methacrylate potassium salt (rGO-SPM) substrate (Fig. 3b and c).…”

“…13g). 102 Non-iridescent structural colors displays in natural light, with bright mixed colors and special reflection under specular lighting. 102 Eu particles are easy to assemble into APCs with non-iridescent structural colors due to their instability and high polydispersity.…”

Designing dual‐mode luminescence in Er3+ doped Y2WO6 microparticles for anticounterfeiting and temperature measurement

“…[15][16][17] Among them, fluorescent anticounterfeiting technology based on rare earth doped materials has been extensively used due to its cheaper cost, good concealment, not being easy to copy, convenient detection, and low toxicity. [18][19][20][21] For example, the Er:Cs 3 YbF 6 :Yb/Er@glass will emit light of different colors under the excitation of a 980 nm laser. 22 However, the use of different excitation for multimode anticounterfeiting has more significance.…”

“…— 14 In order to combat the severe problem of counterfeit and shoddy products, there are currently many anticounterfeiting technologies, such as digital anticounterfeiting technology, quick response code anticounterfeiting technology, radio frequency identification technology, and so forth 15–17 . Among them, fluorescent anticounterfeiting technology based on rare earth doped materials has been extensively used due to its cheaper cost, good concealment, not being easy to copy, convenient detection, and low toxicity 18–21 . For example, the Er:Cs 3 YbF 6 :Yb/Er@glass will emit light of different colors under the excitation of a 980 nm laser 22 .…”

Facile Fabrication of Amorphous Colloidal Array Patterns with Good Mechanical Stability via an Infiltration-Driven Mayer Rod Coating Method

“…However, there are still some defects in practical application for these methods, such as complex instruments, slow assembly process, harsh assembly conditions, or unsuitable for magnified production. Inspired by the idea of rapid removal of solvent as mentioned above, infiltration-driven colloidal assembly method uses porous paper material as the medium, which can rapidly absorb the solvent in the colloidal dispersion (within milliseconds), − thereby quickly fixing the colloidal particles on the paper surface to form an ACA. Because of its rapid, simple, and flexible process, the infiltration-driven colloidal assembly method is extremely suitable for the large-scale preparation of ACA and for easy to design various patterns.…”