Halide perovskites have received tremendous attention due to their fantastic optical and electrical properties. Here, circularly polarized light emission is successfully demonstrated using a simple ...configuration consisting of inorganic perovskite nanocrystals embedded within a predefined handedness cholesteric superstructure stack. The helical structured cholesteric liquid crystal film acts as a selective filter to transform the unpolarized light emission from perovskite nanocrystals into circularly polarized luminescence. The transformation is accompanied by an extraordinary dissymmetry factor (|glum|) up to 1.6, well‐defined handedness, high photoluminescence quantum yield, and full‐color availability. Furthermore, the circularly polarized luminescence is angular dependent and can easily be modulated by shifting the overlap of the reflection band and the emission band. The proposed method is more straightforward and powerful than the previous approaches, offering new opportunities in optoelectronic and photonic devices.
Circularly polarized luminescence is successfully demonstrated from CsPbX3 perovskite nanocrystals enabled by cholestericsuperstructure stacks. Using the cholesteric liquid crystal films with opposite handedness, high dissymmetry factor values of 1.5–1.6 can easily be achieved for the red, green, and blue emission.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A new light‐driven chiral molecular switch doped in a stable blue phase (BP) liquid crystal allows wide optical tunability of three‐dimensional cubic nanostructures with a selective reflection ...wavelength that is reversibly tuned through the visible region. Moreover, unprecedented reversible light‐directed red, green, and blue reflections of the self‐organized three‐dimensional cubic nanostructure in a single film are demonstrated for the first time. Additionally, unusual isothermal photo‐stimulated less ordered BP II to more ordered BP I phase transition was observed in the system.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Self‐powered smart windows are highly attractive for the development of energy‐efficient buildings system, owing to their superior capacities in regulating the energy and information exchange between ...indoor and outdoor environments. Although immense achievement has been made in the self‐powered cholesteric liquid crystal smart window (CLC‐SW) based on triboelectric nanogenerators (TENGs), such a self‐powered manner is limited by some challenges such as the need of the continuous input of external forces, as well as unstable performance owing to inevitable mechanical abrasion of TENGs surface. Here, a fully self‐powered CLC‐SW is developed by leveraging droplet‐based electricity generator (DEG) as a spontaneous and sustained energy reservoir, in which DEG has superior capacities to harvest ceaseless energy from ambient environment and circumvent any additional electrical power input. It is demonstrated that DEG‐driven CLC‐SW exhibits a rapid response and high tunability in the transformation between the transparent state and the hazy state in a wide range of solar spectrum. Moreover, both the transparent and hazy modes can be self‐sustained for a long time, also be reversibly switched by the gentle mechanical pressure loading. The DEG‐driven smart window developed in this work can find applications such as indoor temperature modulation and privacy information protection.
A fully self‐powered cholesteric liquid crystal smart window (CLC‐SW) is developed by the fusion of CLC and droplet‐based electricity generator (DEG), of which the transparency can be switched reversibly between the hazy and transparent state in a facile and energy‐free manner.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Natural self-assembled three-dimensional photonic crystals such as blue-phase liquid crystals typically assume cubic lattice structures. Nonetheless, blue-phase liquid crystals with distinct crystal ...symmetries and thus band structures will be advantageous for optical applications. Here we use repetitive electrical pulses to reconfigure blue-phase liquid crystals into stable orthorhombic and tetragonal lattices. This approach, termed repetitively applied field, allows the system to relax between each pulse, gradually transforming the initial cubic lattice into various intermediate metastable states until a stable non-cubic crystal is achieved. We show that this technique is suitable for engineering non-cubic lattices with tailored photonic bandgaps, associated dispersion and band structure across the entire visible spectrum in blue-phase liquid crystals with distinct composition and initial crystal orientation. These field-free blue-phase liquid crystals exhibit large electro-optic responses and can be polymer-stabilized to have a wide operating temperature range and submillisecond response speed, which are promising properties for information display, electro-optics, nonlinear optics, microlasers and biosensing applications.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Although there have been intense efforts to fabricate large three-dimensional photonic crystals in order to realize their full potential, the technologies developed so far are still beset with ...various material processing and cost issues. Conventional top-down fabrications are costly and time-consuming, whereas natural self-assembly and bottom-up fabrications often result in high defect density and limited dimensions. Here we report the fabrication of extraordinarily large monocrystalline photonic crystals by controlling the self-assembly processes which occur in unique phases of liquid crystals that exhibit three-dimensional photonic-crystalline properties called liquid-crystal blue phases. In particular, we have developed a gradient-temperature technique that enables three-dimensional photonic crystals to grow to lateral dimensions of ~1 cm (~30,000 of unit cells) and thickness of ~100 μm (~ 300 unit cells). These giant single crystals exhibit extraordinarily sharp photonic bandgaps with high reflectivity, long-range periodicity in all dimensions and well-defined lattice orientation.Conventional fabrication approaches for large-size three-dimensional photonic crystals are problematic. By properly controlling the self-assembly processes, the authors report the fabrication of monocrystalline blue phase liquid crystals that exhibit three-dimensional photonic-crystalline properties.
Dimming and scattering control are two of the major features of smart windows, which provide adjustable sunlight intensity and protect the privacy of people in a building. A hybrid photo- and ...electrical-controllable smart window that exploits salt and photochromic dichroic dye-doped cholesteric liquid crystal was developed. The photochromic dichroic dye causes a change in transmittance from high to low upon exposure to sunlight. When the light source is removed, the smart window returns from colored to colorless. The salt-doped cholesteric liquid crystal can be bi-stably switched from transparent into the scattering state by a low-frequency voltage pulse and switched back to its transparent state by a high-frequency voltage pulse. In its operating mode, an LC smart window can be passively dimmed by sunlight and the haze can be actively controlled by applying an electrical field to it; it therefore exhibits four optical states—transparent, scattering, dark clear, and dark opaque. Each state is stable in the absence of an applied voltage. This smart window can automatically dim when the sunlight gets stronger, and according to user needs, actively adjust the haze to achieve privacy protection.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Nematic chiral liquid crystals (CLCs) are characterized by a helical arrangement of nematic LC molecules. A layer of CLC typically exhibits an optical reflection band due to Bragg reflection in the ...helical structure. When several layers of CLC are spin-coated and polymerized on top of each other without a barrier layer in between, defect modes can form in their reflection spectrum. By comparing experimental results and simulations, we investigate the origin of the defect modes, thereby revealing details on the behavior of the materials at the interfaces during deposition. Simulations show that these defect modes can originate from the migration of chiral dopant leading to a layer with a smaller pitch or from a discontinuity in the director orientation at the interface between two layers.
Optically controlled wide‐range beam steering and spectrum scanning are demonstrated by a self‐organized liquid crystal grating. The diffraction angle can be tuned around 30° upon light irradiation. ...In addition, a reversible spectrum scanning system can be constructed using the optical tunable grating. This highly tunable light‐driven grating has great potential in light propagation control and spectroscopy applications.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Highly tunable 3D liquid photonic crystals are demonstrated using low-dc-field-driven polymer-stabilized blue-phase liquid crystals. The central wavelength of the photonic band gap can be reversibly ...shifted to more than 200 nm away from the original position. Besides, by controlling the polymerization-induced morphology variations, the band gap can also be expanded from a bandwidth of around 30 nm to at least 310 nm, the first time a “white” blue phase is observed. Both types of band-gap modulation, namely, shifting and expansion, can be independently manipulated in any crystal axis without affecting the lattice spacings in the other dimensions. We envision polymer-stabilized blue-phase liquid crystals as a fascinating platform for photonic applications, such as 3D lasers, nonlinear optics, and photonic integrated circuits.
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IJS, KILJ, NUK, PNG, UL, UM
The work demonstrates a polarizer-free bistable reflective electro-optical switch that is based on dichroic dye-doped cholesteric liquid crystal (DDCLC). Bistable opaque and transparent states can be ...achieved using the planar and ULH textures of CLC, respectively. In the planar texture, the liquid crystal and dye molecules have a periodic helical structure with axes perpendicular to the substrate surface. They therefore absorb arbitrarily polarized light. In the ULH texture, the liquid crystal and dye molecules twist along the helical axes parallel to the substrate, and allow most of the arbitrarily polarized light to pass. Both the planar and ULH textures of CLC are stable states, and each can be switched to the other by applying a low-frequency (30Hz) electrical field, owing to the electro-hydrodynamic effect. A bistable electro-optical switch has the advantages of being polarizer-free and consuming low power. It can therefore potentially be used in portable information systems.
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