Over 200 °C Broad-Temperature Lasers Reconstructed from a Blue-Phase Polymer Scaffold

In Situ Secondary Growth Method for Dual-Chiral Blue Phase Liquid Crystal Films with Broadly Tunable Hyper-Reflective Photonic Bandgaps

Blue-phase liquid crystals (BPLCs) have shown great potential in hyper-reflective display technology due to their narrow bandgap, high color saturation, and fast response characteristics. However, there remains a significant challenge for achieving open-patternable dual-chiral BPLC films (DH-BP) and precise tuning for efficient hyper-reflection due to the packaging limitations of liquid crystal cells and the complexities of the dynamic bandgap matching principle. In this study, an in situ secondary growth strategy was proposed to successfully fabricate structurally continuous and uniform DH-BP films. Key factors affecting color uniformity were thoroughly analyzed, including the optimization of material structure, surface modification of the polymer template, and control of thickness. Subsequently, inkjet printing and ink diffusion swelling techniques were employed to achieve hyper-reflection in DH-BP films, with a tunable bandgap range of approximately 109 nm (from 576 to 467 nm), and a maximum reflectivity of up to 97%. Finally, a tunable dynamic multi-information encryption strategy was proposed by integrating color, polarization, and hyper-reflection. The method provides new insights into the design of high-saturation, high-reflection displays and has broad application prospects in energy-efficient displays and security technologies.

Stretchable Blue Phase Liquid Crystal Lasers with Optical Stability Based on Small-Strain Nonlinear 3D Asymmetric Deformation

Blue phase liquid crystal (BPLC) lasers exhibit exceptional optical quality and tunability to external stimuli, holding significant promise for innovative developments in the field of flexible optoelectronics. However, there remain challenges for BPLC elastomer (BPLCE) lasers in maintaining good optical stability during stretching and varying temperature conditions. In this work, a stretchable laser is developed based on a well-designed BPLCE with a combination of partially and fully crosslinked networks, which can output a single-peak laser under small deformation (44.429 nm lasing shift at 32% strain) and a broad-temperature range (from -20 to 100 °C). The superior performance can be attributed to the nonlinear 3D asymmetric deformation exhibited by the BPI lattice during stretching, particularly at low deformation rates below 40% strain, which effectively maintains the stability of the body-centered cubic structure (with the maximum strain of this BPLCE up to 220%). Moreover, the BPLCE exhibits excellent thermal stability over a temperature range from -180 to 70 °C with a stopband shift of less than ±10 nm. As a proof-of-concept, the application of BPLCE laser for morphology sensing and 3D mechanical perception is demonstrated, which paves the way for potential applications of flexible optoelectronics.

Tunable Circularly Polarized Luminescence Enabled by Photo-induced Phase Transition in a Blue-phase Liquid Crystal with a Wide Room-temperature Window

Chiral luminescent liquid crystal (LC) materials with switchable circularly polarized luminescence (CPL) signals have received extensive attention, in which the use of light stimulation to achieve different CPL states is of great significance. However, there are very few reports on the generation and regulation of CPL signals enabled by blue phase LC (BPLC). Herein, achieving CPL signal inversion based on the phase transition induced by light/temperature stimulation in a BPLC system with a wide room-temperature window is reported. A binaphthalene azo-based chiral photoswitch (S)-switch 3 with high helical twisted power (HTP) and large HTP variation is synthesized, and a BP system with a wide room temperature range is further fabricated by doping (S)-switch 3 and a fluorescence molecule into a bulk LC. By regulating the doping amount of (S)-switch 3, a phase transition from BP to cholesteric (Ch) phase at room temperature is observed upon 365 nm UV light irradiation or during cooling process, and the polarization inversion of CPL signal is correspondingly found due to the different CPL generation mechanisms of BPLC and CLC. This study provides a new strategy for the flexible regulation of CPL signals in a BPLC system.

Photopatterned Anchoring Stabilizing Monodomain Blue Phases

Blue phase liquid crystals (BPLCs) are chiral self-assembled three-dimensional (3D) periodic structures which have attracted a lot of attention due to their electro-optical properties, relevant for tunable soft photonic crystals and fast-response displays. However, to realize this application potential, controlling the BPLC alignment at the surfaces is crucial, and one way to obtain the desired alignment is by photoalignment patterning. In this article, monodomain BPLC samples with controlled orientation are achieved by imposing different alignment patterns that have a periodicity that is compatible with the size of the BPLC unit cell, using two-step photoalignment with polarized ultraviolet (UV) light. Experiments are complemented by numerical simulations to design striped surface alignment patterns, which induce specific director orientations on the boundary layer of the confined BPLC. By designing the patterns and matching the periodicity to a specific BP material, we can control the orientation of the blue phase unit cell lattice in the sample, including the azimuthal angle. The orientation is measured by the Kossel patterns and matches the optimal configuration predicted by stability analysis using Landau-de Gennes free energy modeling. The detailed structure and reduced symmetry of the BP near the surface are investigated, and the corresponding (meta)stable structures are demonstrated. Overall, we demonstrate that two-step photoalignment patterning is a reliable, relatively simple, and reconfigurable method to achieve a high-quality monodomain BP with controlled and tunable crystalline orientation.

When quantum dots meet blue phase liquid crystal elastomers: visualized full-color and mechanically-switchable circularly polarized luminescence

Polymer-based circularly polarized luminescence (CPL) materials with the advantage of diversified structure, easy fabrication, high thermal stability, and tunable properties have garnered considerable attention. However, adequate and precise tuning over CPL in polymer-based materials remains challenging due to the difficulty in regulating chiral structures. Herein, visualized full-color CPL is achieved by doping red, green, and blue quantum dots (QDs) into reconfigurable blue phase liquid crystal elastomers (BPLCEs). In contrast to the CPL signal observed in cholesteric liquid crystal elastomers (CLCEs), the chiral 3D cubic superstructure of BPLCEs induces an opposite CPL signal. Notably, this effect is entirely independent of photonic bandgaps (PBGs) and results in a high glum value, even without matching between PBGs and the emission bands of QDs. Meanwhile, the lattice structure of the BPLCEs can be reversibly switched via mechanical stretching force, inducing on-off switching of the CPL signals, and these variations can be further fixed using dynamic disulfide bonds in the BPLCEs. Moreover, the smart polymer-based CPL systems using the BPLCEs for anti-counterfeiting and information encryption have been demonstrated, suggesting the great potential of the BPLCEs-based CPL active materials.

Super-Wide Temperature Lasers Spanning from -180 to 240 °C Based on Fully-Polymerized Blue Phase Superstructures

Blue phase liquid crystal (BPLC) lasers have potential applications in displays, sensors, and anti-counterfeiting fields owing to their outstanding optical properties. However, there remain challenges on lasing below 0 °C, which significantly limits the potential application of BPLC lasers in low-temperature environments. In this work, BPLC lasing below 0 °C is realized for the first time in a super-wide temperature range of -180-240 °C using a well-designed fully-polymerized BPLC system with a narrow line width of 0.0881 nm and a low lasing threshold of 37 nJ pulse-1. This fully-polymerized BPLC both effectively avoids low-temperature random crystallization and has excellent compatibility with dye molecules that significantly widen the lasing temperature range below 0 °C. Besides, the variations of laser peak and threshold are also revealed below 0 °C, that is, redshifted laser wavelength and increased threshold value with decreasing temperature, which contribute to a blue-shifted laser signal and a U-shaped lasing threshold in -180-240 °C. These unique laser behaviors can be ascribed to the temperature-dependent anisotropically microstructural deformation of the BP lattice. This work not only opens a door to the development of low-temperature BPLC lasers but also sets out important insights in the design of novel organic optical devices.

Phase-Transition Microcavity Laser

Liquid-crystal microcavity lasers have attracted considerable attention because of their extraordinary tunability and sensitive response to external stimuli, and because they operate generally within a specific phase. Here, we demonstrate a liquid-crystal microcavity laser operated in the phase transition in which the reorientation of liquid-crystal molecules occurs from aligned to disordered states. A significant wavelength shift of the microlaser is observed, resulting from the dramatic changes in the refractive index of liquid-crystal microdroplets during the phase transition. This phase-transition microcavity laser is then exploited for sensitive thermal sensing, enabling a two-order-of-magnitude enhancement in sensitivity compared with the nematic-phase microlaser operated far from the transition point. Experimentally, we demonstrate an exceptional sensitivity of -40 nm/K and an ultrahigh resolution of 320 μK. The phase-transition microcavity laser features compactness, softness, and tunability, showing great potential for high-performance sensors, optical modulators, and soft matter photonics.

Research Progress on Blue-Phase Liquid Crystals for Pattern Replication Applications

Blue-Phase Liquid Crystals (BPLCs) are considered to be excellent 3D photonic crystals and have attracted a great deal of attention due to their great potential for advanced applications in a wide range of fields including self-assembling tunable photonic crystals and fast-response displays. BPLCs exhibit promise in patterned applications due to their sub-millisecond response time, three-dimensional cubic structure, macroscopic optical isotropy and high contrast ratio. The diversity of patterned applications developed based on BPLCs has attracted much attention. This paper focuses on the latest advances in blue-phase (BP) materials, including applications in patterned microscopy, electric field driving, handwriting driving, optical writing and inkjet printing. The paper concludes with future challenges and opportunities for BP materials, providing important insights into the subsequent development of BP.