Background color dependent photonic multilayer films for anti-counterfeiting labeling

A Disposable Thermally Triggered Photonic Crystal Anti-Counterfeiting Tag with Irreversible Response and Multi-Step Color Changes

Thermochromic photonic crystal (PC) is a promising material for anti-counterfeiting applications, but there are still challenges to further improve the anti-counterfeiting performance and the practicability in usage. Here, a disposable thermally triggered PC anti-counterfeiting tag with irreversible response and multi-step color changes is developed based on the thermochromic Silica/(Polyethylene glycol-Ethoxylated trimethylolpropane triacrylate) (SiO2/(PEG-ETPTA)) double-layer film. The fast and irreversible thermal response come from the quick melting and infiltration of PEG-ETPTA into the PCs upon heating. The multi-step color change at different temperatures originated from the regioselective control of the UV curing degree of the PEG-ETPTA layer and the resulting thermochromic temperature of the double-layer film. Therefore, the invisible PC pattern on the tag can be revealed part by part upon heating and became invisible again after overheating, which offered diversified visual effects and enhanced anti-counterfeiting performances.

CsBr-Triggered Reversible Phase Transition of Perovskite Nanocrystals for Advanced Information Encryption and Decryption

Luminescent perovskite nanocrystals (NCs), possessing the advantages of low cost, easy detection, and excellent luminescence, are becoming more and more significant in the fields of information encryption and decryption. Most hydrochromic perovskite NCs for information encryption have moderate reversibility and are easily passively decrypted by water in the moist air, limiting their practical applications. Herein, a lyochromic material is synthesized based on reversible phase transition between luminescent CsPbBr3-HBr (pretreating CsPbBr3 with HBr) and nonluminescent Cs4PbBr6, exhibiting excellent reversibility in 50 cycles triggered by CsBr solution. HBr treatment boosts the ion migration of NCs via diminishing surface ligands and passivating Br vacancy, assisting CsBr concentration acting as a crucial factor in dynamic ion exchange equilibrium between the trigger solution and CsPbBr3-HBr. By utilizing CsPbBr3-HBr as a safety ink, the CsBr-triggered photoluminescence switch has been demonstrated to be reproducible, stable, and reliable for information encryption and decryption.

Dual Responsive Dependent Background Color Based on Thermochromic 1D Photonic Crystal Multilayer Films

In this paper, we present dual responsive one-dimensional (1D) photonic crystal (PC) multilayer films that utilize a high-humidity environment and temperature. Dual responsive 1D PC multilayer films are fabricated on precoated thermochromic film by sequential alternate layer deposition of photo-crosslinkable poly(2-vinylnaphthalene-co-benzophenone acrylate) (P(2VN-co-BPA)) as a high refractive index polymer, and poly(4-vinylpyrollidone-co-benzophenone acrylate) P(4VP-co-BPA) as a low refractive index polymer. The thermochromic film shows a vivid color transition from black to white at 28 °C. Three different colors of thermochromic 1D PC multilayer films are prepared by thickness modulation of P(4VP-co-BPA) layers, and the films on a black background exhibit visible spectrum color only in a high-humidity environment (over 90% relative humidity (RH)). For the three films placed on a hands display, three different composite colors are synthesized by the reflection of light, including yellow, magenta, and cyan, due to the changing of backgrounds from black to white with temperature. Additionally, the films show remarkable color transitions with reliable reversibility. The films can be applied as anti-counterfeiting labels and can be used for smart decoration films. To the best of our knowledge, this is the first report of dual response colorimetric films that change color in various ways depending on temperature and humidity changes, and we believe that it can be applied to various applications.