Photoaligned Nanorod Enhancement Films with Polarized Emission for Liquid-Crystal-Display Applications

A new route towards polarized luminescence: 0D/2D nanocomposites

Combining wide bandgap 2D inorganic materials and blue-light-emitting 0D carbon dots in 0D/2D heterojunction nanocomposites was shown to give rise to unique optical properties and a multifunctional prototype device was developed, capable of polarized light luminescence, modulation and detection.

Integrating Achiral and Chiral Organic Ligands in Zero-Dimensional Hybrid Metal Halides to Boost Circularly Polarized Luminescence

Chiral zero-dimensional hybrid metal halides (0D HMHs) could combine excellent optical properties and chirality, making them promising for circularly polarized luminescence (CPL). However, chiral 0D HMHs with efficient CPL have been rarely reported. Here, we propose an efficient strategy to achieve simultaneously high photoluminescence quantum yield (PLQY) and large dissymmetry factor (glum ), by integrating achiral and chiral ligands into 0D HMHs. Specifically, three pairs of chiral 0D hybrid indium-antimony chlorides are synthesized by combing achiral guanidine with three types of chiral methylbenzylammonium-based derivatives as the organic cations. These chiral 0D HMHs exhibit near-unity PLQY and large glum values up to around ±1×10-2 . The achiral guanidine ligand is not only essential to crystallize these hybrid indium-antimony chlorides to achieve near-unity PLQYs, but also greatly enhances the chirality induction from organic ligands to inorganic units in these 0D HMHs. Furthermore, the choice of different chiral ligands can modify the strength of hydrogen bonding interactions in these 0D HMHs, to maximize their glum values. Overall, this study provides a robust way to realize efficient CPL in chiral HMHs, expanding their applications in chiroptical fields.

Ultrafast dense DNA functionalization of quantum dots and rods for scalable 2D array fabrication with nanoscale precision

Scalable fabrication of two-dimensional (2D) arrays of quantum dots (QDs) and quantum rods (QRs) with nanoscale precision is required for numerous device applications. However, self-assembly-based fabrication of such arrays using DNA origami typically suffers from low yield due to inefficient QD and QR DNA functionalization. In addition, it is challenging to organize solution-assembled DNA origami arrays on 2D device substrates while maintaining their structural fidelity. Here, we reduced manufacturing time from a few days to a few minutes by preparing high-density DNA-conjugated QDs/QRs from organic solution using a dehydration and rehydration process. We used a surface-assisted large-scale assembly (SALSA) method to construct 2D origami lattices directly on solid substrates to template QD and QR 2D arrays with orientational control, with overall loading yields exceeding 90%. Our fabrication approach enables the scalable, high fidelity manufacturing of 2D addressable QDs and QRs with nanoscale orientational and spacing control for functional 2D photonic devices.

An Organic Chiroptical Detector Favoring Circularly Polarized Light Detection from Near-Infrared to Ultraviolet and Magnetic-Field-Amplifying Dissymmetry in Detectivity

Circularly polarized light detection has attracted growing attention because of its unique application in security surveillance and quantum optics. Here, through designing a chiral polymer as a donor, a high-performance circularly polarized light detector is fabricated, successfully enabling detection from ultraviolet (300 nm) to near-infrared (1100 nm). The chiroptical detector presents an excellent ability to distinguish right-handed and left-handed circularly polarized light, where dissymmetries in detectivity, responsivity, and electric current are obtained and then optimized. The dissymmetry in electric current can be increased from 0.18 to 0.23 once an external magnetic field is applied. This is a very rare report on the dissymmetry tunability by an external field in chiroptical detectors. Moreover, the chirality-generated orbital angular momentum is one of the key factors determining the performance of the circularly polarized light detection. Overall, the organic chiroptical detector presents excellent stability in detection, which provides great potential for future flexible and compact integrated platforms.

Unveiling the Localized Exciton-Based Photoluminescence of Manganese Doped Cesium Zinc Halide Nanocrystals

Lead-free metal halide nanocrystals (NCs) have aroused increasing attention due to their unique optoelectronic properties based on localized excitons (LEs). However, the vital influencing factors for the LEs based photoluminescence (PL) are still not well-understood due to the coupling of various intrinsic and extrinsic factors of the NCs. Herein, by engineering the phase, size, morphology, and chemical composition, we are able to decouple the intrinsic and extrinsic factors of manganese doped cesium zinc-halide NCs. We found both the intrinsic metal-halide coordination field and the extrinsic crystal defects have significant influences on the LEs' recombination and energy transfer processes, and hence determine the PL efficiency. Unlike for the free excitons (FEs) based PL, the phase as well as the crystal morphology do not play major roles for the LEs based PL. This work provides a new insight for the study of LE dynamics of metal halide NCs.

Circularly Polarized Luminescence in Zero-Dimensional Antimony Halides: Structural Distortion Controlled Luminescence Thermometer

Materials emitting circularly polarized luminescence (CPL) have been intensively studied for their promising applications in various fields. However, developing tunable and responsive CPL materials in a wide wavelength range remains a great challenge. Here, a pair of chiral (R,R/S,S-DCDA)₃Sb₂Cl₁₂ (DCDA = dimethyl-1,2-cyclohexanediamine divalent cation) shows efficient broadband yellow emission with a photoluminescence (PL) quantum yield of 27.6% with a CPL asymmetry factor of 3 × 10^-3. The associated chiroptical activity is attributed to the efficient chiral transfer as well as the self-trapped exciton emission originating from the large distortion of the inorganic blocks. Notably, (R,R/S,S-DCDA)₃Sb₂Cl₁₂ exhibits a large red-shift emission exceeding 100 nm upon lowering temperature. An excellent linear correlation of the PL wavelength on temperature indicates that the compounds can be used as PL thermometers, which originates from a temperature-dependent linear structural distortion of the [SbCl₆] emitter. This work inspires the potential utilization of CPL-emitting materials as responsive light sources.

Anisotropic Heavy-Metal-Free Semiconductor Nanocrystals: Synthesis, Properties, and Applications

Heavy-metal (Cd, Hg, and Pb)-containing semiconductor nanocrystals (NCs) have been explored widely due to their unique optical and electrical properties. However, the toxicity risks of heavy metals can be a drawback of heavy-metal-containing NCs in some applications. Anisotropic heavy-metal-free semiconductor NCs are desirable replacements and can be realized following the establishment of anisotropic growth mechanisms. These anisotropic heavy-metal-free semiconductor NCs can possess lower toxicity risks, while still exhibiting unique optical and electrical properties originating from both the morphological and compositional anisotropy. As a result, they are promising light-emitting materials in use various applications. In this review, we provide an overview on the syntheses, properties, and applications of anisotropic heavy-metal-free semiconductor NCs. In the first section, we discuss hazards of heavy metals and introduce the typical heavy-metal-containing and heavy-metal-free NCs. In the next section, we discuss anisotropic growth mechanisms, including solution-liquid-solid (SLS), oriented attachment, ripening, templated-assisted growth, and others. We discuss mechanisms leading both to morphological anisotropy and to compositional anisotropy. Examples of morphological anisotropy include growth of nanorods (NRs)/nanowires (NWs), nanotubes, nanoplatelets (NPLs)/nanosheets, nanocubes, and branched structures. Examples of compositional anisotropy, including heterostructures and core/shell structures, are summarized. Third, we provide insights into the properties of anisotropic heavy-metal-free NCs including optical polarization, fast electron transfer, localized surface plasmon resonances (LSPR), and so on, which originate from the NCs' anisotropic morphologies and compositions. Finally, we summarize some applications of anisotropic heavy-metal-free NCs including catalysis, solar cells, photodetectors, lighting-emitting diodes (LEDs), and biological applications. Despite the huge progress on the syntheses and applications of anisotropic heavy-metal-free NCs, some issues still exist in the novel anisotropic heavy-metal-free NCs and the corresponding energy conversion applications. Therefore, we also discuss the challenges of this field and provide possible solutions to tackle these challenges in the future.

Synergism between LDLB and true CD to achieve angle-dependent chiroptical inversion and switchable polarized luminescence emission in nonreciprocal nanofibrous films

Chiroptical nanomaterials including chiralized advanced functional nanofibers have attracted ever-increasing interest in multi-disciplinary fields. Nowadays, electronic circular dichroism (CD) is the most widely used technique to evaluate chiral properties. Numerous studies have shown that the occurrence of linear dichroism and linear birefringence (LDLB) phenomenon in chiral micro-/nano-architectures makes it challenging to distinguish their inherent chiral information. However, tactfully combining LDLB with true circular dichroism (true CD) may lead to a new class of chiroptical materials. In this study, we demonstrate that transparent nanofibrous films infiltrated with poor solvents can show unique LDLB properties, which allows achiral nanofibrous films to exhibit these features regularly opposite Cotton signals by simply flipping the two faces of the same film or even rotating the testing angles of the sample around its optical axis in a single face. More importantly, we can quantitatively distinguish the contribution of LDLB from true CD in the chiral composite nanofibrous system and even effectively combine them into a single unity. This kind of adjustable flexible film material shows outstanding value in the field of optoelectronics. Its large intrinsic LDLB feature and angle-dependent, non-reciprocal transmission for polarized lights are exploited to fabricate programmable polarized light-emitting devices through the resin encapsulation process. This study may provide an easy and powerful way for the construction and implementation of novel polarization optical materials towards future intelligent optical encryption and advanced anti-counterfeiting devices.

Electronic Structure and Excited State Dynamics of Cadmium Chalcogenide Nanorods

The cylindrical quasi-one-dimensional shape of colloidal semiconductor nanorods (NRs) gives them unique electronic structure and optical properties. In addition to the band gap tunability common to nanocrystals, NRs have polarized light absorption and emission and high molar absorptivities. NR-shaped heterostructures feature control of electron and hole locations as well as light emission energy and efficiency. We comprehensively review the electronic structure and optical properties of Cd-chalcogenide NRs and NR heterostructures (e.g., CdSe/CdS dot-in-rods, CdSe/ZnS rod-in-rods), which have been widely investigated over the last two decades due in part to promising optoelectronic applications. We start by describing methods for synthesizing these colloidal NRs. We then detail the electronic structure of single-component and heterostructure NRs and follow with a discussion of light absorption and emission in these materials. Next, we describe the excited state dynamics of these NRs, including carrier cooling, carrier and exciton migration, radiative and nonradiative recombination, multiexciton generation and dynamics, and processes that involve trapped carriers. Finally, we describe charge transfer from photoexcited NRs and connect the dynamics of these processes with light-driven chemistry. We end with an outlook that highlights some of the outstanding questions about the excited state properties of Cd-chalcogenide NRs.

Two-Dimensional Hybrid Perovskitoid Micro/nanosheets: Colorful Ultralong Phosphorescence, Delayed Fluorescence, and Anisotropic Optical Waveguide

Molecular persistent luminescence, such as room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF), have attracted broad attention in the fields of biological imaging, information security, and optoelectronic devices. However, the development of molecular micro/nanostructures combining both RTP and TADF properties is still in an early stage. Herein, a new type of organic metal hybrid perovskitoid (OMHP) two-dimensional (2D) microcrystal has been fabricated through a facile solution method. The long-lived TADF-RTP dual emission can be highly tuned by changing the excitation wavelength, temperature, and decayed time. Moreover, the 2D OMHP microsheet exhibits an asymmetric and anisotropic optical waveguide with low optical loss coefficient, together with extremely high linearly polarized fluorescence-phosphorescence emission (anisotropy = 0.96), which is promising for the development of polarization-sensitive luminescent materials. Therefore, this work not only demonstrates new OMHP showing colorful persistent luminescence under different modes (such as excitation wavelength, temperature, polarization, lifetime, and dimension) but also takes advantage of the 2D micro/nanostructure to provide potential applications as optical logic gates and for delicate multiple information encryption.

Signal Inversion and Amplification of Circularly Polarized Luminescence in a Poly(phenylacetylene)-Based Composite System Assisted by Achiral PMMA

Multichannel regulable circularly polarized luminescence (CPL) is fascinating because of its fundamental and application interest. There are few reports on helical sense (P-/M-helix) modulation and chiral signal amplification of polyacetylenes with the assistance of achiral polymers and further applications in precisely and conveniently regulating CPL handedness and magnitude. Herein, a helical poly(phenylacetylene)-based CPL-active system was constructed, in which CPL inversion occurred by adding achiral PMMA into a helical poly(phenylacetylene)-CHCl₃ solution. Significantly, there is almost 10 times magnification of luminescence dissymmetry factor values (|g_lum|) during this process. The above phenomena could be ascribed to the PMMA-assisted polyene backbone elongation and the formation of a more ordered helical structure for the poly(phenylacetylene)s. More interestingly, the CPL signal can be facilely inverted and switched by simply changing the thickness of the PPhAD/PMMA layer. The temperature-driven dynamic CPL handedness inversion and magnitude modulation can also be achieved. Based on the multiple regulations for CPL, logic operations were developed, and the practical application is further facilitated by designing various CPL patterns. This study establishes effective and convenient strategies to switch the handedness, magnitude, and wavelength of CPL, which may generate a breakthrough in the manufacturing of CPL-active smart materials and devices with promising application potential.

Biomimetic non-classical crystallization drives hierarchical structuring of efficient circularly polarized phosphors

Hierarchically structured chiral luminescent materials hold promise for achieving efficient circularly polarized luminescence. However, a feasible chemical route to fabricate hierarchically structured chiral luminescent polycrystals is still elusive because of their complex structures and complicated formation process. We here report a biomimetic non-classical crystallization (BNCC) strategy for preparing efficient hierarchically structured chiral luminescent polycrystals using well-designed highly luminescent homochiral copper(I)-iodide hybrid clusters as basic units for non-classical crystallization. By monitoring the crystallization process, we unravel the BNCC mechanism, which involves crystal nucleation, nanoparticles aggregation, oriented attachment, and mesoscopic transformation processes. We finally obtain the circularly polarized phosphors with both high luminescent efficiency of 32% and high luminescent dissymmetry factor of 1.5 × 10⁻², achieving the demonstration of a circularly polarized phosphor converted light emitting diode with a polarization degree of 1.84% at room temperature. Our designed BNCC strategy provides a simple, reliable, and large-scale synthetic route for preparing bright circularly polarized phosphors.

Chiral emitters with high photoluminescence quantum yield are desirable for use in circularly polarized LEDs. The authors demonstrate the transfer of chirality from nanoscale copper iodide clusters to microscale chiral luminescent polycrystals by non-classical crystallization.

Determining nanorod dimensions in dispersion with size anisotropy nanoparticle tracking analysis

Control over nanorod dimensions is critical to their application, requiring fast, robust characterisation of their volume and aspect ratio whilst in their working medium. Here, we present an extension of Nanoparticle Tracking Analysis which determines the aspect ratio of nanoparticles from the polarisation state of scattered light in addition to a hydrodynamic diameter from Brownian motion. These data, in principle, permit the determination of nanorod dimensions of any composition using Nanoparticle Tracking Analysis. The results are compared with transmission electron microscopy and show that this technique can additionally determine the aggregation state of the nanorod dispersion if single nanorod dimensions are determined with a complementary technique. We also show it is possible to differentiate nanoparticles of similar hydrodynamic diameter by their depolarised scattering. Finally, we assess the ability of the technique to output nanorod dimensions and suggest ways to further improve the approach. This technique will enable rapid characterisation of nanorods in suspension, which are important tools for nanotechnology.

Solution-Processed Red, Green, and Blue Quantum Rod Light-Emitting Diodes

Solution-processed semiconductor nanocrystals are evolving as potential candidates for future display and lighting applications owing to their size-tunable emission, ultrasaturated colors, and compatibility with large-area flexible substrates. Among them, quantum rods (QRs) are emerging materials for optoelectronic applications, offering polarized emission, high light outcoupling efficiency, color purity, and better stability in solid films. However, synthesizing QRs covering the full visible wavelength region has been a big challenge, particularly in the blue range. Herein, we report for the first time the synthesis of red CdSe/CdS, green CdSe/Zn_xCd_1-xS/ZnS, and blue CdSe/Zn_xCd_1-xS/ZnS QRs and their application in red, green, and blue QR-based light-emitting diodes (QR-LEDs). We have improved the charge injection balance into the QRs through embedding a poly(methyl methacrylate) (PMMA) layer between the emissive and electron transport layers. The thin PMMA electron-blocking layer (EBL) suppresses the excessive electron flux and thus promotes charge injection balance and pushes the recombination zone back to the QR layer, resulting in 1.35×, 1.2×, and 1.7× peak external quantum efficiency improvement for red, green, and blue QR-LEDs, respectively. The efficiency roll-off of green and blue QR-LEDs with an EBL is less than 50% at maximum current density. The proposed red, green, and blue QR-LEDs open up an avenue toward further improving the light source efficiency and stability focusing on real device applications.

Electrically Switchable Anisometric Carbon Quantum Dots Exhibiting Linearly Polarized Photoluminescence: Syntheses, Anisotropic Properties, and Facile Control of Uniaxial Orientation

Carbon quantum dots (CQDs) have been extensively explored in diverse fields because of their exceptional features. The nanometric particles with photoluminescence (PL) benefit various optical and photonic applications. However, the majority of previous reports have mainly focused on either unpolarized or circular-polarized (CP) PL. Linearly polarized (LP) emission of CQDs is limited mainly because of their isometric shape and difficulties in macroscopic orientation control. Herein, we report syntheses of anisometric CQDs and facile control of the uniaxial orientation on a macroscopic scale, which results in linearly polarized photoluminescence (LP-PL). The anisometric CQDs are synthesized from rigid-rod-shaped precursors and evenly dispersed in the rod-like liquid crystal (LC) host. As-synthesized CQDs exhibit a PL quantum yield as high as 35% in chloroform. In addition to uniform alignment, facile directional switching of the elongated CQD is established by employing the electrical responsiveness of the CQD and host LC. Therefore, the dichroic photophysical properties of anisometric CQDs have been beneficially adopted for fabrications of polarization-sensitive and electrically switchable PL devices. Also, anisometric CQDs are embedded in polymer films with molecular orientational patterns and clearly recognized by LP-PL.

Mini-LED Backlight Technology Progress for Liquid Crystal Display

As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to greatly improve the contrast, color gamut, dark state and other element of the display performance of LCD displays. Mini-LED backlight technology is undoubtedly the most ideal solution to realize a highly dynamic range display of LCD displays, and has been widely commercialized in many fields such as TVs, tablet computers, notebook computers, and car monitors. This review mainly introduces the efforts made by researchers to eliminate the halo effect, thinning of the backlight module and reducing the backlight power consumption. The application of quantum dot technology in backlight is also presented. We predict that the number of Mini-LED backlight partitions is expected to reach a level of more than 3000 in the future, further utilizing the advantages of the small size in local dimming, but it will also inevitably be challenged by some issues such as power consumption and heat dissipation.

Mechanisms of plant cell wall surveillance in response to pathogens, cell wall-derived ligands and the effect of expansins to infection resistance or susceptibility

Cell wall integrity is tightly regulated and maintained given that non-physiological modification of cell walls could render plants vulnerable to biotic and/or abiotic stresses. Expansins are plant cell wall-modifying proteins active during many developmental and physiological processes, but they can also be produced by bacteria and fungi during interaction with plant hosts. Cell wall alteration brought about by ectopic expression, overexpression, or exogenous addition of expansins from either eukaryote or prokaryote origin can in some instances provide resistance to pathogens, while in other cases plants become more susceptible to infection. In these circumstances altered cell wall mechanical properties might be directly responsible for pathogen resistance or susceptibility outcomes. Simultaneously, through membrane receptors for enzymatically released cell wall fragments or by sensing modified cell wall barrier properties, plants trigger intracellular signaling cascades inducing defense responses and reinforcement of the cell wall, contributing to various infection phenotypes, in which expansins might also be involved. Here, we review the plant immune response activated by cell wall surveillance mechanisms, cell wall fragments identified as responsible for immune responses, and expansin's roles in resistance and susceptibility of plants to pathogen attack.

Quantum-Rod On-Chip LEDs for Display Backlights with Efficacy of 149 lm W-1 : A Step toward 200 lm W-1

Efficient white light-emitting diodes (LEDs) with an efficacy of 200 lm W^-1 are much desirable for lighting and displays. The phosphor-based LEDs in use today for display applications offer poor color saturation. Intensive efforts have been made to replace the phosphor with quantum-dot-based downconverters, but the efficiency and stability of these devices are still in their infancy. Quantum rods (QRs), nanoparticles with an elongated shape, show superior properties such as relatively larger Stokes shifts, polarized emission, and high light out-coupling efficiency in the solid-state. However, these QRs usually suffer from poor optical quality for PL wavelengths < 550 nm. Herein, a gradient alloyed CdSe/Zn_x Cd_{1- x} S/ZnS and CdSe/CdS/ZnS core/shell/shell QR downconverters showing high efficacy LEDs covering a wide color gamut are reported. These QRs show high stability and a precisely tunable photoluminescence peak. The engineered shell thickness suppresses energy transfer and thus maintains the high quantum yield in the solid-state (81%). These QR-based LEDs attain an efficacy of 149 lm W^-1 (@10mA) and wide color gamut (118% NTSC), which is exceedingly higher than state-of-the-art quantum dots and phosphor-based on-chip LEDs.

Thermomechanically controlled fluorescence anisotropy in thin films of InP/ZnS quantum dots

Macroscopic scale sources of polarized light play a fundamental role in designing light-emitting devices. In this communication we report the formation of nano- and macro-scale ordered, layered assemblies of InP/ZnS quantum dots (QDs) exhibiting fluorescence anisotropy (FA), as well as thermo- and mechano-responsive properties. The long-range organization of small, quasi-isotropic nanoparticles was achieved by introducing liquid crystal molecules to the surface of QDs, without the need to use an organic matrix. Melting/crystallization of the ligand at 95 deg. C translated to a reversible reconfiguration of QDs thin film between 2D layered and body-centered cubic structures, characteristic for a temperature range below and above the melting point, respectively. The low-temperature, layered structure exhibited mechano-responsiveness which was key to introduce and control the sample alignment. Interestingly, transverse and parallel alignment modes of QDs layers were achieved, depending on the temperature of mechanical shearing. As prepared QD samples exhibited fluorescence anisotropy strongly correlated to the macroscopic orientation of the layers. Correlated small-angle X-ray diffraction (SAXRD) and fluorescence spectroscopy studies confirmed the mm-scale alignment of the thin films of QDs. Such films may be advantageous for developing efficient, densely packed, and uniform macro-scale FA sources.

Polarized Electroluminescence Emission in High-Performance Quantum Rod Light-Emitting Diodes via the Langmuir-Blodgett Technique

Due to their anisotropic structure, quantum rods (QRs) feature unique properties that differ from quantum dots, such as suppression of non-radiative Auger recombination and linearly polarized light emission. Despite many potential advantages, the progress of QR-based light-emitting diodes (QR-LEDs) is left behind due to the difficulty in aligning QRs. In this study, polarized electroluminescence emission is reported in high-performance QR-LEDs by employing the Langmuir-Blodgett (LB) technique. The adoption of the LB technique successfully produces a highly dense and smooth QR film with a high degree of alignment. As a result, the aligned QR films exhibit polarized photoluminescence emission with a degree of linear polarization of 2.1. Advantageous features of the LB technique, such as nondestructiveness, precise thickness control, and the nonnecessity of an additional matrix material, allow to fabricate QR-LEDs with the same procedure as the standard spin coating-based scheme. The device is fabricated via the LB technique, which shows excellent device performance, such as the low turn-on voltage of 1.8 V, peak luminance of 56 287 cd m^-2 , and peak external quantum efficiency (EQE) of 10.33%. Furthermore, these devices clearly exhibit an indication of polarized electroluminescence emission, which opens new opportunities for QRs in display technologies.

Wood-Derived Carbon Materials and Light-Emitting Materials

Wood is a sustainable and renewable material that naturally has a hierarchical structure. Cellulose, hemicellulose, and lignin are the three main components of wood. The unique physical and chemical properties of wood and its derivatives endow them with great potential as resources to fabricate advanced materials for use in bioengineering, flexible electronics, and clean energy. Nevertheless, comprehensive information on wood-derived carbon and light-emitting materials is scarce, although much excellent progress has been made in this area. Here, the unique characteristics of wood-derived carbon and light-emitting materials are summarized, with regard to the fabrication principles, properties, applications, challenges, and future prospects of wood-derived carbon and light-emitting materials, with the aim of deepening the understanding and inspiring new ideas in the area of advanced wood-based materials.

Stable bright perovskite nanoparticle thin porous films for color enhancement in modern liquid crystal displays

Cesium-lead halide perovskite nanoparticles are a promising class of luminescent materials for color and efficient displays. However, material stability is the key issue to solve before we can use these materials in modern displays. Encapsulation is one of the most efficient methods that can markedly improve the stability of perovskite nanoparticles against moisture, heat, oxygen, and light. Thus, we urgently need a low-cost, reliable, and device-compatible encapsulation method for the integration of nanomaterials into display devices. Here, we propose a facile encapsulation method to stabilize perovskite nanoparticles in thin polymer porous films. Using porous polymer films, we achieved good photoluminescence stability in the harsh environment of high temperature, high humidity and strong UV illumination. The good UV stability benefitted from the unique optical properties of the porous film. Besides, we observed photoluminescence enhancement of CsPbBr₃ nanoparticle films in a high humidity environment. The stable CsPbBr₃ nanoparticle thin porous film provides high brightness (236 nits) and great color enhancement for LCDs and is characterized by simple fabrication with easy scalability, thus it is very suitable for modern LCDs.

Polarization-Sensitive Halide Perovskites for Polarized Luminescence and Detection: Recent Advances and Perspectives

While halide perovskites (HPs) have achieved enormous success in the field of optoelectronic applications, much attention has been recently drawn to the unique polarization sensitivity of HPs, either intrinsic or extrinsic, which makes HPs a potential candidate for innovative applications in directly polarized luminescence and detection. Herein, the research status in the field of polarization-sensitive HPs, including linear polarization and circular polarization, is comprehensively summarized. To evaluate the effectiveness of HPs in generating and detecting linearly or circularly polarized light, the principles and characterization methods of polarized luminescence and detection are introduced. Sequentially, the state-of-the-art development of the strategies that induce the linear or circular polarization characteristics of HPs is systematically reviewed, based on which the application of polarization-sensitive HPs in the field of polarization luminescence and detection are summarized. Moreover, the current challenges and opportunities are discussed, and prospects of the future development in this promising field are outlined.

Enantiomeric Switching of the Circularly Polarized Luminescence Processes in a Hierarchical Biomimetic System by Film Tilting

Circularly polarized luminescence (CPL) switching has attracted great attention due to the potential applications in chiral photonics and electronics. However, the lack of examples to achieve switchable CPL within a single material in the dry solid state hampers the scope of applications. Herein, we demonstrate a crystalline chiral polymer film as a polarizing medium consisting of radially assembled twisted crystallites, where achiral aggregation-induced emissive luminogens (AIEgens) are confined between the twisted crystalline stacks, eventually yielding handedness-switchable CPL by simple film tilting. Hierarchically organized twisted crystallites create the selective reflection activity of the polarizing medium. Upon film tilting, enantiomeric switching is realized by selectively collecting transmitted and reflected CPL components. The confined AIEgens in the crystalline polarizing system show a great enhancement of the luminescence efficiency. Moreover, the approach is general with broadband activity, and various AIEgens could be applied to generate full-color-tunable CPL. Additionally, the rigid and continuous nature of this polarizing system affords enhanced optical stability and facile modulation, developing a general route for designing chiroptical materials.

Thermally Stable Quantum Rods, Covering Full Visible Range for Display and Lighting Application

Recently, quantum rods (QRs) have been studied heavily for display and lighting applications. QRs offer serious advantages over the quantum dots such as higher light out-coupling coefficient, and polarized emission. The QR enhancement films double liquid crystal display efficiency. However, it is still a challenge to synthesize good quality green (λ_em  ≈ 520 nm) and blue (λ_em  ≈ 465 nm) emitting QRs, due to very large bathochromic shift during the shell growth. Furthermore, until now, the presence of cadmium in high-quality QRs is inevitable, but due to its toxicity, RoHS has restricted the amount of cadmium in consumer products. In this article, low Cd core-shell QRs, with a narrow-band luminescence spectrum tuned in the whole visible range, are prepared by replacing Cd with Zn in a one-pot post-synthetic development. These QRs possess the good thermal stability of photoluminescence properties, and therefore, show high performance for the on-chip LED configuration. The designed white LEDs (WLEDs) are characterized by a high brightness of 120000 nits, and color gamut covering 122% NTSC (90% of BT2020), in the 1931CIE color space. Additionally, these LEDs show a high luminous efficiency of 115 lm W^-1 . Thus, these quantum rod LED are perfectly viable for display backlighting and lighting applications.

Metal Halide Perovskite Nanorods: Shape Matters

Quasi-1D metal halide perovskite nanorods (NRs) are emerging as a type of materials with remarkable optical and electronic properties. Research into this field is rapidly expanding and growing in the past several years, with significant advances in both mechanistic studies of their growth and widespread possible applications. Here, the recent advances in 1D metal halide perovskite nanocrystals (NCs) are reviewed, with a particular emphasis on NRs. At first, the crystal structures of perovskites are elaborated, which is followed by a review of the major synthetic approaches toward perovskite NRs, such as wet-chemical synthesis, substrate-assisted growth, and anion exchange reactions, and discussion of the growth mechanisms associated with each synthetic method. Then, thermal and aqueous stability and the linear polarized luminescence of perovskite NRs are considered, followed by highlighting their applications in solar cells, light-emitting diodes, photodetectors/phototransistors, and lasers. Finally, challenges and future opportunities in this rapidly developing research area are summarized.

Cd-Rich Alloyed CsPb1- x Cd x Br3 Perovskite Nanorods with Tunable Blue Emission and Fermi Levels Fabricated through Crystal Phase Engineering

One-dimensional semiconductor nanostructures have already been used for a variety of optoelectronic applications. Metal halide perovskites have emerged in recent years as promising high-performance optoelectronic materials, but reports on 1D nanorods (NRs) of all-inorganic halide perovskites are still scarce. This work demonstrates a synthetic strategy toward cesium-based inorganic perovskite NRs by exploiting composition-controlled crystal phase engineering. It is accomplished for Cd-rich mixed-cation CsPb1- x Cd x Br3 nanocrystals, where the initial 1D hexagonal perovskite phase drives the growth of the 1D NRs, as supported by first-principles calculations. The band gaps of the resulting NRs are tunable by varying the Cd-content, and the highly uniform CsPb0.08Cd0.92Br3 NRs (with an average length of 84 nm and width of 16 nm) exhibit a true blue-color emission centered at 460 nm, with a high quantum yield of 48%. Moreover, this work also demonstrates the tunability of the Fermi levels in the films made of CsPb1- x Cd x Br3 alloyed nanocrystals, where samples with highest Cd content show an increase of the electron concentration and a related increase in the conductivity.

Liquid-Crystal-Mediated Geometric Phase: From Transmissive to Broadband Reflective Planar Optics

Planar optical elements that can manipulate the multidimensional physical parameters of light efficiently and compactly are highly sought after in modern optics and nanophotonics. In recent years, the geometric phase, induced by the photonic spin-orbit interaction, has attracted extensive attention for planar optics due to its powerful beam shaping capability. The geometric phase can usually be generated via inhomogeneous anisotropic materials, among which liquid crystals (LCs) have been a focus. Their pronounced optical properties and controllable and stimuli-responsive self-assembly behavior introduce new possibilities for LCs beyond traditional panel displays. Recent advances in LC-mediated geometric phase planar optics are briefly reviewed. First, several recently developed photopatterning techniques are presented, enabling the accurate fabrication of complicated LC microstructures. Subsequently, nematic LC-based transmissive planar optical elements and chiral LC-based broadband reflective elements are reviewed systematically. Versatile functionalities are revealed, from conventional beam steering and focusing, to advanced structuring. Combining the geometric phase with structured LC materials offers a satisfactory platform for planar optics with desired functionalities and drastically extends exceptional applications of ordered soft matter. Some prospects on this rapidly advancing field are also provided.

Linearly Polarized Emission from Shear-Induced Nematic Phase Upconversion Nanorods

Lanthanide-doped particles exhibit unique polarization-dependent luminescence due to the anisotropic crystalline local symmetry surrounding the emitter. Precise control of the orientation of particles shows great significance for exploiting the luminescent polarization and their potential applications. Here, we demonstrated a facile polypropylene-aided shear-driven method to obtain large-scale orientationally ordered upconversion nanorods, showing a liquid-crystalline nematic phase. Upconversion nanorods with low aspect ratios were well-aligned with the crystalline c-axis along the shearing direction using monodispersed colloid nanorods as the nanoink. The order parameter of aligned upconversion nanorods can reach up to 0.95. The nematic upconversion nanorods demonstrated strong polarization-dependent luminescence with the high degrees of polarization of the ⁴F_9/2 sublevels at 657 and 661 nm being 0.47 and 0.59, respectively. Taking advantage of these mesoscopic well-aligned upconversion nanorods, their peculiar polarized emissions are potentially useful for some interdisciplinary applications such as polarization-sensitive bioprobes and anticounterfeiting.

Inkjet-printed aligned quantum rod enhancement films for their application in liquid crystal displays

Semiconductor quantum rods (QRs) show a polarized emission, which opens up the possibility of the enhancement of both brightness and color for liquid crystal displays (LCD) in the form of quantum rod enhancement films (QREFs) for LCD backlights. However, the QR alignment over a large area, suitable for displays, is a challenge. Inkjet printing of QREFs, introduced here, allows fabrication of well-aligned, uniform QREFs on photoaligned substrates using optimized QR inks. We observed that the ink composition and printing conditions affect the QR alignment quality significantly. A relative humidity of 50% with an exposure energy of 1 J cm^-2 for the photoalignment process provided optimal conditions for QREFs. We have successfully shown a good QR alignment for 2.5-inch films and were able to align QRs in multiple layers. Thus, fabricated QREFs show a polarization ratio of 7.2 : 1 for the emitted light. These QREFs were combined with a blue LED and deployed as a backlight unit for an LCD which shows a brightness of ∼250 nits with an optical efficiency of ∼8%, reaching an NTSC of 109% in a CIE1976 color space. Thus, these printed QREFs, over a large area, provide an unprecedented increase of 77% in the optical efficiency of the LCDs and simultaneously offer better color performance.

Luminescent Down-Conversion Semiconductor Quantum Dots and Aligned Quantum Rods for Liquid Crystal Displays

Herein, emerging applications of luminescent semiconductor nanocrystals are addressed, such as quantum dots and quantum rods as down-conversion materials used in liquid crystal displays (LCD). Their precisely tunable emission wavelengths and narrow emission bandwidths offer high color purity resulting in a wide color gamut with vivid colors for LCDs. Anisotropic materials, such as quantum rods, have the additional advantage of polarized emission, which can bring a significant improvement to the efficiency of LCD displays. The basic optical properties of these nanomaterials are considered, with a focus on quantum rods, and the challenges and progress in their assembly are discussed. Different techniques for quantum rod alignment are introduced such as shear-oriented, electric field and magnetic field assisted assembly, mechanical rubbing, stretching, and electrospinning. The photoalignment approach allows for an easy arrangement of quantum rods in-plane, and the implications of this method to patterning are considered. Different configurations of LCDs utilizing semiconductor quantum dots and quantum rods as down-conversion layers are also presented, and the potential applications that are enabled by the wide range of emerging materials are highlighted.

Magnetic and Electric Control of Circularly Polarized Emission through Tuning Chirality-Generated Orbital Angular Momentum in Organic Helical Polymeric Nanofibers

Circularly polarized light emission promotes the development of smart photonic materials for advanced applications in chiral sensing and information storage. The orbital angular momentum is a unique property for organic chiral helical materials. In this work, a type of organic chiral polymeric nanowires is designed with strong chirality induced orbital angular momentum. Under the stimulus of an external magnetic field of 600 mT, circularly polarized emission from the chiral polymeric nanowire becomes more pronounced, where the g factor increases from 0.21 to 0.3. The observed phenomena mainly originate from the chirality-dependent orbital angular momentum. Moreover, the orbital angular momentum in helical chiral nanowire structures can be suppressed by inhibiting electron transport in a helical way to diminish circularly polarized light emission at room temperature.

Chemically Synthesized Carbon Nanorods with Dual Polarized Emission

We realized the synthesis of carbon nanorods-monodisperse colloidal particles with a length of 50 nm and a width of 20 nm-which can be considered an addition to the family of light-emitting carbon-based nanostructures. Their anisotropic shape is determined by the use of the surfactant aminopropylisobutyl polyhedral oligomeric silsesquioxane, and their optical properties originate from domains of polycyclic aromatic hydrocarbons incorporated within an inorganic framework. The nanorods show dual polarized emission with a quantum yield of 15-20% and emission anisotropy of ∼0.3, which changes from blue (460 nm) to yellow (565 nm) depending on the excitation wavelength. These carbon nanorods expand the range of light-emitting carbon nanomaterials available for optoelectronic and biolabeling applications.

A self-assembled nanoparticle cluster array fabricated using nematic-isotropic phase separation on a functionalized surface

The manipulation of a large number of nanoparticles (NPs) is an interesting but challenging task. Here, we demonstrate a new method to fabricate an NP cluster array, in which the shape and size of each NP cluster can be controlled. The method involves the use of the solubility contrast of NPs in the isotropic and nematic liquid crystal (LC) media, and the isotropic-preference difference depending on the types of the surfaces. The former mechanism is used to trap NPs within the isotropic domain, the size of which is simply manipulated by adjusting temperature. The latter mechanism is used to control the location of isotropic pockets in the continuous nematic phase. By controlling the volume and location of the isotropic pocket, one can simply create various types of NP cluster arrays. This method does not involve the use of any external field, and may be applicable to other types of NPs, including ferroelectric or ferromagnetic materials, thereby expanding its applicability.

Tunable Upconverted Circularly Polarized Luminescence in Cellulose Nanocrystal Based Chiral Photonic Films

Integrating chromophores into chiral photonic crystals to fabricate materials that exhibit circularly polarized luminescence (CPL) is promising as this method allows efficient manipulation of the spontaneous emission within photonic bandgaps (PBGs). However, tuning the wavelength of CPL and the dissymmetry factor ( g_lum) in a convenient and accurate manner remains a significant challenge. Here, right-handed, tunable upconverted CPL (UC-CPL) emission was achieved by integrating multiple emissive, upconverting nanoparticles into cellulose nanocrystal based chiral photonic films that had tunable PBGs. Glycerol was used to tune the PBGs of the chiral photonic films, which yielded tunable UC-CPL emission at 450 and 620 nm with a tailored g_lum. Moreover, humidity responsive UC-CPL at blue wavelength was obtained from glycerol-composite photonic film, with a g_lum that ranged from -0.156 to -0.033. It was possible because the PBG and chirality of photonic composite was responded to the relative humidity. This work gives valuable insight into tunable and stimuli-responsive CPL photonic systems.

Perovskite nanowire-block copolymer composites with digitally programmable polarization anisotropy

One-dimensional (1D) nanomaterials with highly anisotropic optoelectronic properties are key components in energy harvesting, flexible electronics, and biomedical imaging devices. 3D patterning methods that precisely assemble nanowires with locally controlled composition and orientation would enable new optoelectronic device designs. As an exemplar, we have created and 3D-printed nanocomposite inks composed of brightly emitting colloidal cesium lead halide perovskite (CsPbX₃, X = Cl, Br, and I) nanowires suspended in a polystyrene-polyisoprene-polystyrene block copolymer matrix. The nanowire alignment is defined by the programmed print path, resulting in optical nanocomposites that exhibit highly polarized absorption and emission properties. Several devices have been produced to highlight the versatility of this method, including optical storage, encryption, sensing, and full-color displays.

In situ synthesis and macroscale alignment of CsPbBr3 perovskite nanorods in a polymer matrix

We report an in situ catalyst-free strategy to synthesize inorganic CsPbBr3 perovskite nanorods in a polymer matrix (NRs-PM) with good dimensional control, outstanding optical properties and ultrahigh environmental stability. Polarization photoluminescence (PL) imaging with high spatial resolution was carried out for the first time on single nanorod (NR) and shows a relatively high local polarization ratio (∼0.4) consistent with theoretical predictions based on a dielectric contrast model. We further demonstrate that macroscale alignment of the CsPbBr3 nanorods can be achieved through mechanically stretching the NRs-PM films at elevated temperature, without deteriorating the optical quality of the NRs. A polarization ratio of 0.23 is observed for these aligned NRs-PM films, suggesting their potential as polarized down-converters to increase the light efficiency in liquid crystal display (LCD) backlights.

Ultrathin CsPbX3 Nanowire Arrays with Strong Emission Anisotropy

1D nanowires of all-inorganic lead halide perovskites represent a good architecture for the development of polarization-sensitive optoelectronic devices due to their high absorption efficient, emission yield, and dielectric constants. However, among as-fabricated perovskite nanowires with the lateral dimensions of hundreds nanometers so far, the optical anisotropy is hindered and rarely explored owing to the invalidating of electrostatic dielectric mismatch in the physical dimensions. Here, well-aligned CsPbBr₃ and CsPbCl₃ nanowires with thickness T down to 15 and 7 nm, respectively, are synthesized using a vapor phase van der Waals epitaxial method. Strong emission anisotropy with polarization ratio up to ≈0.78 is demonstrated in the nanowires with T < 40 nm due to the electrostatic dielectric confinement. With the increasing of thickness, the polarization ratio remarkably reduces monotonously to ≈0.17 until T ≈140 nm; and further oscillates in a small amplitude owing to the wave characteristic of light. These findings not only represent a demonstration of perovskite-based polarization-sensitive light sources, but also advance fundamental understanding of their polarization properties of perovskite nanowires.

Laser Rewritable Dichroics through Reconfigurable Organic Charge-Transfer Liquid Crystals

Charge-transfer materials based on the self-assembly of aromatic donor-acceptor complexes enable a modular organic-synthetic approach to develop and fine-tune electronic and optical properties, and thus these material systems stand to impact a wide range of technologies. Through laser-induction of temperature gradients, in this study, user-defined patterning of strongly dichroic and piezoelectric organic thin films composed of donor-acceptor columnar liquid crystals is shown. Fine, reversible control over isotropic versus anisotropic regions in thin films is demonstrated, enabling noncontact writing/rewriting of micropolarizers, bar codes, and charge-transfer based devices.

Uncovering the Circular Polarization Potential of Chiral Photonic Cellulose Films for Photonic Applications

Circularly polarized light (CPL) is central to photonic technologies. A key challenge lies in developing a general route for generation of CPL with tailored chiroptical activity using low-cost raw materials suitable for scale-up. This study presents that cellulose films with photonic bandgaps (PBG) and left-handed helical sense have an intrinsic ability for circular polarization leading to PBG-based CPL with extraordinary |g | values, well-defiend handedness, and tailorable wavelength by the PBG change. Using such cellulose films, incident light ranging from near-UV to near-IR can be transformed to passive L-CPL and R-CPL with viewing-side-dependent handedness and |g | values up to 0.87, and spontaneous emission transformed to R-CPL emission with |g | values up to 0.68. Unprecedented evidence is presented with theoretical underpinning that the PBG effect can stimulate the R-CPL emission. The potential of cellulose-based CPL films for polarization-based encryption is illustrated. The evaporation-induced self-assembly coupled with nanoscale mesogens of cellulose nanocrystals opens new venues for technological advances and enables a versatile strategy for rational design and scalable manufacturing of organic and inorganic CPL films for photonic applications.