Herein, based on the recently developed magnetic-induced self-assembly techniques, we designed a novel, simple and low-cost method to fabricate a special class of photonic crystals with double photonic band-gap hetero-structures, and eventually achieved the purpose of modulating the optical diffraction color of the structural colors. The method greatly simplifies the fabrication of photonic crystals with multiple photonic band-gap hetero-structures and extends the modulation means of the optical diffraction color of structural colors. Furthermore, it is worth noting that due to the resulting structural colors that are derived from the double photonic band-gap hetero-structures consisting of double diffraction peaks and presenting a magnetic switching effect through the application and withdrawal of the magnetic fields (0.05 T), which is more difficult to be imitated by those of chemical dyes and pigments, a kind of novel photonic anti-counterfeiting label has been prepared with these structural colors. Due to the widespread counterfeiting of various commercial objects and the urgent requirements of forgery protection, the photonic anti-counterfeiting label demonstrated in our work will undoubtedly find applications in meeting the growing anticounterfeiting needs.

Invisible photonic printing, an emerging printing technique, is particularly useful for steganography and watermarking for anti-counterfeiting purposes. However, many challenges exist in order to realize this technique. Herein, we describe a novel photonic printing strategy targeting to overcome these challenges and realize fast and convenient fabrication of invisible photonic prints with good tenability and reproducibility. With this novel photonic printing technique, a variety of graphics with brilliant colors can be perfectly hidden in a soft and waterproof photonic-paper. The showing and hiding of the latent photonic prints are instantaneous with magnet as the only required instrument. In addition, this strategy has excellent practicality and allows end-user control of the structural design utilizing simple software on a PC.

No abstract

A visually readable and highly stable self-display photonic humidity sensor has been fabricated through the fast magnetically induced self-assembly of carbon-encapsulated superparamagnetic colloidals, followed by an instant radical polymerization to fix the photonic crystal structures inside a polyacrylamide glycol gel matrix. Because of the use of magnetic assembly and radicalpolymerization, we can quickly and conveniently prepare the photonic humidity sensor on a large scale with arbitrary shape which has an important significance in large-scale industrial production. The photonic humidity sensor can self-display brilliant colors from navy blue to light red as the relative humidity changes from 11% to 97%. The whole shift of the reflection wavelength is nearly 160 nm, which almost covers the whole visual region and its intensity is readable by the naked eye. In addition, cycle tests demonstrate that the photonic humidity sensor has a good stability and reproducibility in its diffraction signal. Therefore, coupled with low cost and no power consumption, the photonic humidity sensor system can realize colorimetric detection of humidity, similarly to pH indicator paper.

No abstract