Reconfigurable polymer-templated liquid crystal holographic gratings via visible-light recording

Optofluidic tunable broadband distributed Bragg reflector based on liquid crystal polymer composites

A dynamically reconfigurable liquid crystal (LC) photonic device is an important research field in modern LC photonics. We present a type of continuously tunable distributed Bragg reflector (DBR) based on LC polymer composites modulated via a novel optofluidic method. LC-templated DBR films are fabricated by photopolymerization under visible standing wave interference. The influences of the incident angle, incident light intensity, and content of ethanol as a pore-forming additive on the reflection behavior are discussed in detail. Then, the LC-templated DBR films are integrated into microfluidic channels and reversibly refilled by different organic solvents. The reconfigurable characteristics of optofluidic DBRs were demonstrated by changing the average refractive index (RI) of the mixed liquids and adjusting the flow rates, resulting in the dynamic and continuous variation of the reflection band within a specific visible light band. It is anticipated that the prototype optofluidic LC device will hopefully be applied to some specific scenarios where conventional means of regulation, such as electric, optical, and temperature fields, are unsuitable and possibly boost the development of microfluidic analysis techniques based on structural color.

Orthogonal Reconstruction of Upconversion and Holographic Images for Anticounterfeiting Based on Energy Transfer

Crosstalk-free reconstruction of multiple images within a single element can greatly boost the image capacity and information security. We herein demonstrate a viable approach by integrating upconversion and holographic images into a single holographic polymer nanocomposite. The holographic image is reconstructed through photopolymerization-induced phase separation under a 460 nm laser and identifiable under room light, while the upconversion image recognizable under a 980 nm laser is photopatterned via spatially photobleaching of the dye embedded in the upconversion nanoparticle (UCNP) shell under 365 nm light. To this end, the lanthanide-doped UCNP in the core/shell/shell nanostructure of NaYF₄:20%Yb³⁺,0.5%Tm³⁺@NaYF₄@SiO₂ is designed, and the dye, fluorescein isothiocyanate (FITC), is fixed in the outermost SiO₂ shell via the amine-isothiocyanate reaction and the subsequent sol-gel reaction. Energy transfer from the core of the UCNP to FITC embedded in the shell is critical to boosting the contrast of the upconversion image, which dials the emission color from blue to yellow-green. It is also found that the upconversion image can be brightened by increasing the UCNP content while the holographic image is weakened when the UCNP content is over 15 wt %. This study paves a new way toward advanced anticounterfeiting.