Advanced liquid crystal-based switchable optical devices for light protection applications: principles and strategies

Synthesis of 2D PtSe2 Nanolayers on Glass Substrates and Their Integration in Near-Infrared Light Shutters

PtSe2 has asserted its key role among the emerging 2D transition metal dichalcogenides, however, its simplified growth process with controlled number of layers, high crystalline quality, and on inexpensive substrates is still challenging. Here, we report the synthesis details of PtSe2 layers on soda lime glass substrates by selenization of predeposited Pt layers using the thermally assisted conversion method at atmospheric pressure. PtSe2 syntheses are confirmed by X-ray photoelectron spectroscopy and Raman analysis. The layers were further investigated with transmission electron microscopy and optical ellipsometry, revealing the thickness and its dependence on the metal precursor sputtering time. Finally, the integration of PtSe2 as transparent conductive layers in polymer-dispersed liquid crystal structures operating as near-infrared light shutters is demonstrated and device performance is discussed. The proposed simple and inexpensive synthesis approach opens up new directions toward PtSe2 potential technological applications, including ITO-free optoelectronics.

Recent Advances in Smart Windows Based on Photo-Responsive Liquid Crystals Featuring Phase Transition

A smart window is an optical dimming device with intelligent functions that can control its relevant performances through external stimuli, achieving functions such as privacy protection and temperature regulation. Light is an ideal stimulus for regulating smart windows, which is noninvasive and allows self-adaptable manipulation of materials. This review highlights recent significant achievements in smart windows constructed by photo-responsive liquid crystals (LCs) systems that can undergo the transition between different phases. The smart windows based on photo-responsive LCs are used in a plethora of areas, including privacy protection, absorption glass, building decoration, energy saving, and climate modulation applications. The review concludes with a brief perspective on some significant challenges and opportunities for the future development of photo-responsive smart windows, which is crucial for expanding the applications of smart windows and improving their performances.

Low-Voltage Haze Tuning with Cellulose-Network Liquid Crystal Gels

Being key components of the building envelope, glazing products with tunable optical properties are in great demand because of their potential for boosting energy efficiency and privacy features while enabling the main function of allowing natural light indoors. However, windows and skylights with electric switching of haze and transparency are rare and often require high voltages or electric currents, as well as not fully meet the stringent technical requirements for glazing applications. Here, by introducing a predesigned gel material we describe an approach dubbed "Haze-Switch" that involves low-voltage tuning of the haze coefficient in a broad range of 2-90% while maintaining high visible-range optical transmittance. The approach is based on a nanocellulose fiber gel network infiltrated by a nematic liquid crystal, which can be switched between polydomain and monodomain spatial patterns of optical axis via a dielectric coupling between the nematic domains and the applied external electric field. By utilizing a nanocellulose network of nanofibers ∼10 nm in diameter we achieve <10 V dielectric switching and <2% haze in the clear state, as needed for applications in window products. We characterize physical properties relevant to window and smart glass technologies, like the color rendering index, haze coefficient, and switching times, demonstrating that our material and envisaged products can meet the stringent requirements of the glass industry, including applications such as privacy windows, skylights, sunroofs, and daylighting.

Adaptive focal lengths in white light focusing Fresnel lenses enabled by reflective-type and phase-only spatial light modulator

Fresnel zone plates (FZPs) are widely used in integrated optical systems to meet new cutting-edge demands for photonic integration and device miniaturizing. However, their use in applications of cross-scale fabrication still faces several obstacles, such as low efficiency, fixed focal length, single wavelength, large size, and complicated fabrication. Here, we first examine a novel adaptive focal length in white light focusing by using reflective-type and phase-only spatial light modulator (RLC-SLM) based on a liquid crystal on silicon. The device achieves a maximum diffraction efficiency of approximately 38% at primary focal points of binary phase-type FZPs throughout the visible range (red, green, and blue wavelengths). The RLC-SLM focuses the light of the desired wavelength while other sources are defocused. White light focusing and color separation are demonstrated by sequentially and additively switching different FZPs. These recent advances show that optically tunable FRZs are promising potential candidates to enhance adaptive camera systems, microscopes, holograms, and portable and wearable devices, thereby opening up novel possibilities in optical communications and sensing.

A simple and robust aptasensor assembled on surfactant-mediated liquid crystal interface for ultrasensitive detection of mycotoxin

Here, a simple aptasensing approach is represented to sensitively detect ochratoxin A (OTA) as one of the most perilous mycotoxins with carcinogenic, nephrotoxic, teratogenic, and immunosuppressive sequels on human health. The aptasensor is based on the alteration in the orientational order of liquid crystal (LC) molecules at the surfactant-arranged interface. Homeotropic alignment of LCs is achieved by the interaction of the surfactant tail with LCs. By perturbing the alignment of LCs due to the electrostatic interaction of the aptamer strand with the surfactant head, a colorful polarized view of the aptasensor substrate is induced drastically. While OTA causes the re-orientation of LCs to a vertical state by forming an OTA-aptamer complex that induces darkness of the substrate. This study shows that the length of the aptamer strand impacts the efficiency of the aptasensor; longer strand results in the greater disruption of LCs, and therefore, increases the aptasensor sensitivity. Hence, the aptasensor can determine OTA in the linear concentration range of 0.1 fM-1 pM as low as 0.021 fM. The aptasensor is capable to monitor OTA in grape juice, coffee drink, corn, and human serum real samples. The proposed LC-based aptasensor provides a cost-effective, easy-to-carry, operator-independent, and user-friendly array with great potential to develop portable sensing gadgets for food quality control and health care monitoring.

Coupling Ti doping with oxygen vacancies in tungsten oxide for high-performance photochromism applications

A series of Ti-doped W₁₈O₄₉ samples were prepared using a convenient solvothermal route. Due to the synergistic effect of doped Ti and oxygen vacancies, the samples showed excellent visible-light photochromic properties. Their performances as light-printable rewritable paper and smart windows showed great application value and promotion value.