Showing papers in "Journal of Materials Chemistry C in 2019"

Blue organic light-emitting diodes: current status, challenges, and future outlook

Abstract: The recent progress of efficiency improvement, emission color tuning, and lifetime elongation of blue organic light-emitting diodes (OLEDs) is reviewed. The latter is one of the most important bottlenecks for OLED development. The current status of blue light-emitting material design with emission mechanisms such as fluorescence (F), phosphorescence (Ph), thermally activated delayed fluorescence (TADF), and hybridized local and charge transfer (HLCT) is introduced in the first part of this review. Compared to red and green devices, the long exciton lifetime of the high energy triplet exciton in a blue OLED is the one of the main issues. To avoid the accumulation of high energy triplet excitons in the emitter for blue OLEDs, assisted triplet–triplet fluorescence (TTF) and Hyperfluorescence™ are employed to harvest the triplet excitons. In the second part of this review, we focus on issues from an application viewpoint: what are the requirements of blue OLEDs for display and lighting technologies in terms of efficiency, color, and lifetime? Key performance metrics of blue OLEDs with different technologies over time are summarized. Independent of technology, the trend is similar: the external quantum efficiency improves for the first stage of research, followed by color tuning, and then finally lifetime elongation. The state-of-the-art device performance of blue OLEDs with various emission mechanisms is illustrated. Although Ph- and TADF-emission based devices show satisfactory efficiency and electroluminescence (EL) spectra, despite having a lower efficiency TTF-emission based devices are the mainstream for real applications due to their relatively long operation lifetime. Blue Ph-OLEDs have the potential for lighting applications with suitable material selection and device design. We collected the published results and tried our best to make a fair comparison of the operation lifetime among different technologies. Finally, we discuss the possible future outlook from different viewpoints including new materials, device designs, and applications of blue OLEDs.

Recent progress on highly sensitive perovskite photodetectors

Abstract: Perovskite photodetectors (PPDs), which combine the advantages of perovskite semiconductor materials with superior optical and electronic properties and solution-processed manufacturing, have emerged as a new class of revolutionary optoelectronic devices with potential for various practical applications. Encouraged by the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of perovskite materials with interesting optoelectronic properties, increasing research attention is focused on the development of high performance PPDs. In this review, the recent progress on emerging PPDs is comprehensively summarized from the perspective of device physics and materials science. The strategies for extending the spectral response range of PPDs and improving the performance of devices are investigated. Furthermore, the methods for realizing narrowband photodetectors are also discussed, where filter-free and self-filter narrowband PPDs are achieved based on the concept of charge collection narrowing. Meanwhile, the promising future directions in this research field are proposed and discussed, including multifunctional PPDs, perovskite–organic hybrid photodetectors, flexible and transparent PPDs, self-powered PPDs, and photodetector systems and arrays. This review provides valuable insights into the current status of highly sensitive PPDs and will spur the design of new structures and devices to further enhance their photo-detection performances and meet the need of versatility in practical application.

Superior electromagnetic interference shielding 3D graphene nanoplatelets/reduced graphene oxide foam/epoxy nanocomposites with high thermal conductivity

Abstract: How to rationally design the microstructure of polymer nanocomposites to significantly improve their electromagnetic interference shielding effectiveness (EMI SE) is still a great challenge. Herein, we developed a template method for fabricating 3D porous graphene nanoplatelets/reduced graphene oxide foam/epoxy (GNPs/rGO/EP) nanocomposites, in which 3D rGO foam embedded with GNPs constructs a 3D electrical and thermal conductive network in the EP matrix. The 3D rGO framework resolves the agglomeration problem of GNPs, acts as an efficient bunch of channels for electrical transport and attenuates the entered electromagnetic wave. Benefiting from this 3D nanohybrid framework, the GNPs/rGO/EP nanocomposites containing 0.1 wt% rGO and 20.4 wt% GNPs exhibit an EMI SE value of 51 dB in the X-band range, an almost 292% improvement relative to the rGO/EP nanocomposites (∼13 dB) and 240% enhancement compared with the GNPs/EP nanocomposites without 3D microstructures (∼15 dB) and an excellent thermal conductivity of 1.56 W mK−1 and electrical conductivity up to 179.2 S m−1. This work provides a new strategy for the design of muti-functional epoxy nanocomposites for EMI shielding and efficient heat dissipation.

Enhanced energy-storage performance with excellent stability under low electric fields in BNT–ST relaxor ferroelectric ceramics

Abstract: Relaxor ferroelectrics are promising candidates for pulsed power dielectric capacitor applications because of their excellent energy-storage properties. Different from most relaxor ferroelectrics whose energy-storage density was improved by increasing the breakdown strength and reducing the remanent polarization, in this study, anti-ferroelectric (AFE) AgNbO3 (AN) was used to partially substitute the relaxor ferroelectric 0.76Bi0.5Na0.5TiO3–0.24SrTiO3 (BNT–ST) of morphotropic phase boundary (MPB) composition to reduce the remanent polarization while maintaining large maximum polarization. In this way, a large recoverable energy-storage density (2.03 J cm−3) was obtained in the BNT–ST–5AN ceramics under lower electric field of 120 kV cm−1, which is superior to other lead-free energy-storage materials under similar electric fields. Moreover, excellent temperature (25–175 °C) and frequency (1–100 Hz) stabilities are achieved. This performance demonstrates that the BNT–ST–5AN ceramics form a promising class of dielectric capacitive material for high-temperature pulsed power capacitors with large energy-storage density.

Gallium oxide solar-blind ultraviolet photodetectors: a review

Abstract: In recent years, solar-blind ultraviolet (UV) photodetectors have attracted significant attention from researchers in the field of semiconductor devices due to their indispensable properties in the fields of high-temperature event monitoring, anti-terrorism, security and ad hoc network communication. As an important member of the third-generation semiconductors, β-Ga2O3 is considered to be one of the most promising candidates for solar-blind UV detectors due to its ultra-wide band gap (∼4.9 eV), economic efficiency, high radiation resistance and excellent chemical and thermal stability. Herein, we provide a comprehensive review on Ga2O3-based solar-blind UV photodetectors, with a detailed introduction of the developmental process of material growth methods and device manufacturing in the past decade. We classify the currently reported Ga2O3-based solar-blind UV photodetectors (mainly including photoconductive detectors, heterogeneous PN junction detectors and Schottky junction detectors) and summarize their respective superiorities and potentials for improvement. Finally, considering the actual application requirements, we put forward some meaningful suggestions, including energy band engineering and homogeneous epitaxy, for the future development of Ga2O3 material growth and device manufacturing.

An overview of stretchable strain sensors from conductive polymer nanocomposites

Abstract: There is a growing demand for stretchable strain sensors because of their potential applications in various emerging fields, such as human motion detection, health monitoring, wearable electronics, and soft robotic skin. Recently, strain sensors based on flexible conductive polymer composites (FCPCs) composed of conductive materials and a stretchable elastomer have received intensive attention owing to their high stretchability, good flexibility, excellent durability, tunable strain sensing behaviors, and ease of processing. Here, we systematically summarize the recent progress of stretchable strain sensors based on FCPCs. This review covers the classification and sensing mechanisms as well as the influence of multiple factors on the sensing behaviors of FCPC based strain sensors with detailed examples.

A review on inkjet printing of nanoparticle inks for flexible electronics

Abstract: Inkjet printing is recognised as an efficient method for direct deposition of functional materials on flexible substrates in predesigned patterns owing to simple processing, low cost and higher adaptability for large scale fabrication of electronic devices, sensors, light emitting diodes, etc. Inks used in inkjet printing mostly consist of organic polymers, metal nanoparticles and carbon materials such as graphene and carbon nanotubes. For effectiveness of the printing process, the fluid dynamic parameters such as viscosity and surface tension, as well as dimensionless quantities such as the Weber number, Reynolds number, and Ohnesorge number, must be within a suitable limit. More frequently, this process suffers due to the formation of a coffee ring during the post printing process, which affects the morphology as well as electrical conductivity of the printed pattern. In this review, we have summarized the various aspects of inks such as fluid dynamical parameters of inks, mechanism of the coffee ring formation, different types of ink preparation strategies and their applications in sensors, thin film transistors, and energy storage devices.

Achieving high discharge energy density and efficiency with NBT-based ceramics for application in capacitors

Abstract: High-performance capacitors, which have high energy storage density as well as high discharge efficiency, are desired. In this study, we have designed and prepared novel and high quality (1 − x)(0.65Bi0.5Na0.5TiO3–0.35Bi0.1Sr0.85TiO3)–x(K0.5Na0.5NbO3) [(1 − x)(BNT–BST)–xKNN, x = 0, 0.04, 0.06, 0.08, and 0.10] ceramics that demonstrated a remarkable energy storage capability, high efficiency, and ultrafast discharge speed. Particularly, the 0.94(BNT–BST)–0.06KNN ceramic possessed an excellent stored energy storage density (Ws = ∼3.13 J cm−3) and recoverable energy storage density (Wr = ∼2.65 J cm−3), and maintained a relatively high efficiency (η = ∼84.6%) at a relatively low electric field of 180 MV m−1, which is superior to those of the lead-free BNT-based energy-storage materials. Moreover, excellent temperature (20–120 °C) and frequency (1–100 Hz) stabilities of the 0.94(BNT–BST)–0.06KNN ceramic were also achieved. More importantly, the 0.94(BNT–BST)–0.06KNN ceramic exhibited an ultrafast discharge rate (τ0.9 = ∼1.01 μs), a high level of discharge energy density (Wd −1.21 J cm−3), and excellent reliability in energy storage performance by consecutive cycling. Moreover, this study also provides an effective approach to attain large energy-storage capability along with high efficiency in BNT-based ceramics for application in pulsed power capacitors.

Strategies to fabricate metal–organic framework (MOF)-based luminescent sensing platforms

Abstract: Metal–organic frameworks (MOFs), with diverse framework architectures, have evolved as next-generation utility multifunctional hybrid materials. One of the key features of MOFs is their luminescence properties, which can be generated from the building ligands, emissive metal ions, guest ions, or molecules used to construct them as well as from their catalytic activities. MOFs with luminescent properties have been used as excellent platforms for designing luminescent sensors. Their chemically tailorable framework with specific host–guest interactions plays an important role in selectively sensing metal ions, small organic molecules, and biomolecules. This review intends to summarize the recent advances in the construction of MOF-based sensors for chemical sensing and biosensing. Specially, we focus on the fabrication strategies of MOF-based luminescent sensors, and summarize their sensing mechanisms in detail. Also, the major challenges and constraints for this research field are discussed.

Viologen-based electrochromic materials and devices

Abstract: Considerable interest is raised by organic materials owing to their exceptional performance in electronic and optoelectronic applications. Among these, electrochromic materials (EC) that can be switched between a distinct color and a bleached state exhibiting high contrast, multicolor and improved long-term stability are attractive in the fabrication of electrochromic devices (ECDs). Ionic materials, in particular, have received persistent attention owing to their tunable optical and electronic properties. 4,4′-Bipyridinium salts, commonly called viologens (V2+), are a well-recognized class of electrochromic materials that exhibit three reversible redox states, namely, V2+ (dication, pale yellow colored/colorless) ↔ V+˙ (radical cation, violet/blue/green) ↔ V0 (neutral, colorless). The electrochromic properties of these materials can be modulated by varying the nitrogen substituents on the pyridyl ‘N’; also, besides this, varying the counter ions with specific functionalities has been shown to enhance the electrochromic behavior, such as switching time, cycling stability and device performance. Although ECDs based on viologens are well regarded for their low operational voltages, they exhibit certain disadvantages such as low cycle life and poor efficiency of the device in the long term. Extensive efforts have been made to fine tune the EC properties of viologens, either through alteration or by adding suitable electrochromic counter electrode materials, which includes the incorporation of conducting polymers in the device set-up and/or the addition of complementary redox species. Optimization of the device parameters has shown that the addition of such external agents has a positive effect on the overall device performance. This review describes recent developments in the synthesis of viologen-based electrochromes with co-redox species and their ECD performance.

From nanofibers to ordered ZnO/NiO heterojunction arrays for self-powered and transparent UV photodetectors

Abstract: Uniformly aligned electrospun nanofiber arrays are important building blocks for high-performance functional devices and device arrays. However, it remains a challenge to prepare perfectly aligned and large area nanofiber arrays using common electrospinning. In this work, a modified electrospinning method utilizing three assisted electrodes for nanofiber collection was proposed to achieve uniformly aligned and millimeter-long ZnO and NiO nanofiber arrays (more than 90% of nanofibers aligned to within ±4° of the desired direction), which were further fabricated into ZnO/NiO heterojunction arrays with a density of 106 cm−2. Photodetectors (PDs) based on the as-prepared ZnO/NiO heterojunction arrays exhibited excellent ultraviolet (UV) selective and self-powered detection properties because of the properly matched energy bands of ZnO and NiO. A maximum responsivity of 0.415 mA W−1 and a short rise/decay time of 7.5 s/4.8 s at 0 V bias of the device markedly outstripped the reference ZnO nanofiber array device. The three-assisted-electrode electrospinning method of this work offers new chances in novel nanostructure design and high-performance device fabrication.

Ultralight CoNi/rGO aerogels toward excellent microwave absorption at ultrathin thickness

Abstract: Ultrathin thickness ( 3.5 GHz. The investigation of the absorption mechanism revealed that moderate dielectric loss, magnetic loss, good impedance matching and the porous structure contributed to the high microwave absorption. This work opens up a potential strategy to prepare excellent microwave absorbents with ultrathin thickness and ultralow density.

Microwave-assisted synthesis of carbon dots and their applications

Abstract: Carbon dots, an emerging class within the carbon allotrope family, have gained significant attention largely due to their versatile and tunable physico-chemical and optical properties. These quasi-spherical carbon nanomaterials, less than 10 nm in size, can be prepared using numerous synthesis strategies resulting in unique properties that can be exploited for a myriad of applications. This review examines the bottom-up synthesis of these dots with a focus on their microwave-assisted synthesis, which can be used to prepare hydrophilic, hydrophobic or even amphiphilic carbon dots. It also investigates their application to multiple fields including sensing, bioimaging, solar cells and catalysis. Finally, a discussion of the challenges and perspectives are provided.

Enhanced energy storage properties in sodium bismuth titanate-based ceramics for dielectric capacitor applications

Abstract: There are imperious demands for developing eco-benign energy storage materials with high-performance in a sustainable society. In this paper, we introduce Sr0.85Bi0.1□0.05TiO3 (SBT) and NaNbO3 (NN) into Bi0.5Na0.5TiO3 (BNT) ceramics through compositional design. The introduction of Sr2+ ions and vacancies at the A-sites constructs relaxor ferroelectrics according to order–disorder theory. The introduction of Nb5+ ions at the B-sites is confirmed to have two major implications. In one way, it boosts a higher induced polarization due to its intrinsic larger polarizability and overall stronger degree of diffuseness. In another, it contributes to forming a core–shell microstructure, as proven using transmission electron microscopy, promoting the breakdown strength (BDS) to a higher level. With the above strategies, our BNT–SBT–4NN ceramics demonstrate excellent energy storage performances with simultaneously ultrahigh energy storage density (W ∼ 3.78 J cm−3), recoverable energy storage density (Wrec ∼ 3.08 J cm−3) and efficiency (81.4%). Furthermore, the ceramics possess excellent discharge energy density (Wd = 0.854 J cm−3) and rapid discharge speed (t0.9 ∼ 100 ns) in a wide temperature range, proving their high application potential. Our results break through the bottleneck of BNT-based ferroelectrics with a general recoverable energy storage density of lower than 3 J cm−3, making the BNT–SBT–4NN ceramic a powerful candidate material for use in energy storage applications.

Flexible transparent conducting electrodes based on metal meshes for organic optoelectronic device applications: a review

Abstract: Transparent conducting electrodes (TCEs) have played a pivotal role in driving the continuous development of optoelectronics technologies, which include organic optoelectronic applications. In recent years, there has been huge interest in designing innovative TCEs to replace the conventional indium tin oxide (ITO) electrodes, which suffer from complex fabrication issues and are incompatible with flexible, wearable electronic devices. In this regard, TCEs based on metal meshes are considered to be the best candidates because of their inherently high electrical conductivity, optical transparency, mechanical robustness and, more importantly, cost-competitiveness. In this review, we describe the technology developments of metal mesh-based transparent conductors and their applications in organic optoelectronic devices, including organic and perovskite solar cells, organic light emitting diodes, supercapacitors, electrochromic devices etc. Specifically, we discuss the fundamental features, optoelectronic properties, fabrication techniques and device applications of metal mesh TCEs. We also highlight the important criteria for evaluating the performance of metal mesh electrodes and propose some new research directions in this emerging field.

Excellent comprehensive energy storage properties of novel lead-free NaNbO3-based ceramics for dielectric capacitor applications

Abstract: NaNbO3 (NN) is generally considered as one of the most promising lead-free antiferroelectric (AFE) perovskite materials with the advantages of low cost, low density and nontoxicity. However, the metastable ferroelectric phase causes a large remanent polarization (Pr) at room temperature, seriously hindering the achievement of excellent energy storage properties. Although via the strategy of lowering the radius of B-site ions and polarizability, a number of AFE NaNbO3-based solid solutions with double polarization–electric field loops are successfully constructed, the hysteresis losses are still too large and the Pr value cannot be reduced to near zero. In this study, Bi(Mg2/3Nb1/3)NbO3 (BMN) was chosen to partially substitute the pure NaNbO3 with the intention of enhancing antiferroelectricity and constructing a local random field simultaneously. These short-range interactions effectively suppress the hysteresis loss and Pr, and slim hysteresis loops were observed in the NN–BMN ceramics. A high charged energy density (3.4 J cm−3) and recoverable energy storage density (2.8 J cm−3) with high efficiency (82%) were achieved under 300 kV cm−1 for NN–0.10BMN. Superior stabilities and underdamped discharge abilities were also achieved for NN–0.15BMN with a slightly smaller recoverable energy storage density (2.4 J cm−3) but even higher efficiency (90%). The results reported here demonstrate great potential of the designed NN–BMN ceramics for high-temperature capacitors.

Carbon quantum dots: an emerging material for optoelectronic applications

Abstract: As an emerging class of luminescent nanomaterials, carbon quantum dots (CQDs) have recently shown enormous potential for optoelectronic applications on account of their characteristic broad emission, tunable fluorescence emission, high thermal stability, and low cytotoxicity. In this review, we will update the latest research progress achieved in CQDs, including their synthesis, optical properties, luminescence mechanism, and applications in optoelectronics. Mainly reviewed here are their room temperature phosphorescence, delayed fluorescence properties, as well as their optoelectronic applications including light-emitting diodes, lasing, solar cells, and photodetectors. Finally, current problems and challenges of CQD-based optoelectronics applications are discussed with an eye on future development. We hope that this review will provide critical insights to inspire new exciting discoveries in the area of CQDs from both fundamental and practical standpoints so that the realization of their potential in the optoelectronic areas can be facilitated.

Ultrathin high-performance electromagnetic wave absorbers with facilely fabricated hierarchical porous Co/C crabapples

Abstract: Extremely strong electromagnetic wave (EMW) absorption with a minimum reflection loss (RL) of −56.9 dB at 9.3 GHz at an absorber thickness of only 1.92 mm was observed for the hierarchical porous cobalt (Co)/carbon (C) crabapples, lab-made via a facile solvothermal reaction coupled with a following carbon reduction treatment. At an ultrathin thickness of 1.4 mm, the hierarchical porous Co/C crabapples (50 wt% filling content) provided 90% EMW absorption over a broad bandwidth of 5.9 GHz. A broad bandwidth of 5.8 GHz at 2.0 mm thickness was still achieved at a low filling ratio of 30 wt% filler content. This broad-band EMW absorption resulted from the synergy of cobalt and carbon with a significantly improved impedance matching level. The strong magnetism of cobalt endowed the composites with strong absorption ability and thin absorber thickness. The unique porous structural features also contributed to the enhanced EMW absorption by inducing multi-scatterings. The hierarchical porous Co/C crabapples with high absorbing performance together with ultrathin absorber thickness can be applied as a promising EMW absorption material.

All-inorganic cesium lead halide perovskite nanocrystals: synthesis, surface engineering and applications

Abstract: Recently, all-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) have attracted much attention because of their excellent photophysical properties and promising applications in diverse fields. In this review article, the synthetic methods have been briefly summarized first, followed by the morphological control of CsPbX3 NCs. To improve their photophysical properties as well as stability, surface passivation strategies, such as chemical treatment and encapsulation approaches, are used and have been summarized. Their representative applications in various fields, including light emitting diodes (LEDs), solar cells, photodetectors, lasers and photocatalysis, have been introduced. Finally, a brief outlook of this field has been proposed to point out some important challenges and possible solutions.

Waxberry-like hierarchical Ni@C microspheres with high-performance microwave absorption

Abstract: The rational design of the microstructure of magnetic carbon-based composites has become a popular strategy to enhance their microwave absorption properties. Herein, with Ni-containing metal–organic framework as the self-sacrificing precursor, we have successfully prepared waxberry-like Ni@C microspheres as novel microwave absorbing materials, which artfully integrated the advantages of core–shell configuration and hierarchical architecture. The effects of the pyrolysis temperature on the microstruture, carbon content, relative graphitization degree, magnetic properties, and electromagnetic parameters were carefully investigated. The composite that was pyrolyzed at 700 °C (Ni@C-700) exhibited desirable microwave absorption performance, including a strong reflection loss intensity of −73.2 dB and a broad qualified bandwidth of 4.8 GHz with an applied thickness of 1.8 mm. The electromagnetic analysis revealed that such good performance of Ni@C-700 was benefited from both the well-matched impedance and decent attenuation ability. The superiority of this unique microstruture was also validated by comparing it with some homologous composites and isolated core–shell Ni@C nanoparticles. It is believed that these results may provide a new pathway to promote the electromagnetic applications of conventional magnetic carbon-based composites by optimizing their microstructure.

Luminescent perovskite quantum dots: synthesis, microstructures, optical properties and applications

Abstract: In the past few years, metal halide perovskite quantum dots and nanocrystals have been extensively explored due to their unique optoelectronic properties and extensive application prospects. In this review article, we provide an overview of the synthesis, microstructure variation, luminescence properties and potential applications of hybrid organic–inorganic perovskites and all-inorganic perovskites. Firstly, several widely used wet chemical methods for synthesizing perovskite quantum dots are summarized, and then the related structures and morphologies of different perovskites as well as the relationship between the microstructure and optical properties are given. Additionally, correlative metal halides with B-site ion replacement or doping and some strategies to improve the stability of perovskite materials are highlighted. Subsequently, a brief introduction about their potential applications in light-emitting diodes, photodetectors and lasing is presented. Finally, some conclusions and outlooks will be introduced. It is expected that this review article will provide valuable insights into the current status of perovskite luminescent materials and stimulate new ideas and further research on their practical applications.

Ultralight MXene-based aerogels with high electromagnetic interference shielding performance

Abstract: This work for the first time reports a freeze-casting route for fabricating an ultralight MXene aerogel (ρ < 10 mg cm−3) without using external supporters. It shows that this route is scalable for producing MXene aerogels with large sizes. These aerogels contain micro-sized pores determined by the morphology of ice crystals and demonstrate strong absorption ability for various organic solvents. More strikingly, they show excellent EMI shielding performance (up to 75 dB) with extremely low reflection (<1 dB). This gives rise to a specific shielding effectiveness of 9904 dB cm3 g−1 owing to the ultralow density of the aerogels.

A flexible pressure sensor based on an MXene–textile network structure

Abstract: High-performance pressure sensors have attracted considerable attention recently due to their promising applications in touch displays, wearable electronics, human–machine interfaces, and real-time physiological signal perception. However, the “functionality” of a sensor is generally incompatible with “simple” fabrication strategies. Therefore, strategies that are less equipment-intensive and less expensive are required for enhancing the sensor performance. Here, we propose a flexible piezoresistive pressure sensor based on MXene–textile prepared by a facile dip-coating process. Benefiting from the excellent electrical properties of MXene and the abundant wavy surface of cotton textile, this pressure sensor exhibits high sensitivity (12.095 kPa−1 for the range 29–40 kPa and 3.844 kPa−1 for the range less than 29 kPa) with a rapid response time of 26 ms, and excellent cycling stability (5600 cycles). The real-time monitoring of human physiological signals such as wrist pulse, voice detection, and finger movements can be achieved by using this MXene–textile sensor. In addition, sensory arrays were successfully applied in the pressure distribution mapping of a key, demonstrating that the pressure sensor can be used as part of wearable devices and human–machine interfaces to sense pressure.

A new strategy to realize high comprehensive energy storage properties in lead-free bulk ceramics

Abstract: Lead-free bulk ceramics have attracted increasing interest for electrical energy storage in pulsed power systems because of their superior mechanical properties, environment-friendliness, high power density and fast charge/discharge rate. Although considerable efforts have been made to design a large amount of lead-free bulk ceramics for energy storage applications, there is still a lack of scientific and feasible guidelines of how to explore new material systems with large recoverable energy density (Wrec), high energy storage efficiency (η) and excellent thermal stabilty, which are the three key parameters for energy storage applications. In this work, a strategy (coexistence of nanodomains and polar nanoregions via composition optimization) was proposed to achieve high comprehensive energy storage properties in lead-free bulk ceramics. NaNbO3–Bi(Mg0.5Zr0.5)O3 ceramics were selected as an example to verify the feasibility of this strategy. Encouragingly, both a high Wrec of 2.31 J cm−3 and a high η of 80.2% were achieved in 0.93NaNbO3–0.07Bi(Mg0.5Zr0.5)O3 (0.93NN–0.07BMZ) ceramics under 255 kV cm−1, while keeping excellent thermal stability over 20 °C to 170 °C with the variation of Wrec < 10%, which is superior to other reported lead-free bulk ceramics. Compared with other lead-free bulk ceramics, the 0.93NN–0.07BMZ ceramic is a promising material for high-temperature pulsed power capacitors. Most importantly, this work provides a significant guideline for exploring a series of new high-performance lead-free dielectric ceramics for next generation advanced pulsed power capacitors in the future.

Gas sensing with heterostructures based on two-dimensional nanostructured materials: a review

Abstract: Gas sensors are being used in diverse applications in security, food safety, environmental monitoring, indoor air quality monitoring, personal healthcare, etc. During the past decade, two-dimensional (2D) nanostructured materials have attracted intense attention because of their unique chemical and physical properties. They have demonstrated promising potential for gas sensing devices because of their large surface-to-volume ratio, high surface sensitivity, and excellent semiconducting properties. Combining 2D nanostructured materials with other dimensional materials also holds great promise for developing high-performance gas sensors. This review presents a comprehensive summary of recent progress in gas sensors with advanced heterostructures based on 2D nanostructured materials. Furthermore, the fundamental sensing mechanisms of different types of gas sensors are systematically discussed, and key device architectures and their performances are summarized. Finally, the challenges and prospects for the future development of each type of gas sensor are addressed to promote better sensing-device architectures.

Ideal blue thermally activated delayed fluorescence emission assisted by a thermally activated delayed fluorescence assistant dopant through a fast reverse intersystem crossing mediated cascade energy transfer process

Abstract: A novel blue thermally activated delayed fluorescence (TADF) organic light-emitting diode with an emitting layer made up of a TADF assistant dopant and a pure blue-emitting TADF emitter was developed to demonstrate a pure blue color, a high external quantum efficiency, suppressed efficiency roll-off, and an improved lifetime. Two fused B–N type blue TADF emitters with a narrow emission spectrum were used as the blue emitters and the narrow blue emission was harvested by a TADF assistant dopant through a reverse intersystem crossing mediated cascade energy transfer process. A high external quantum efficiency of 31.4%, pure blue emission color of (0.13, 0.15), significant reduction of the efficiency roll-off and more than 10 times lifetime extension were simultaneously achieved using the TADF assisted TADF process.

Design for high energy storage density and temperature-insensitive lead-free antiferroelectric ceramics

Abstract: Dielectric capacitors with high power density and excellent temperature stability are highly demanded in pulsed power systems. AgNbO3-based lead-free antiferroelectric ceramics have been proven to be a promising candidate for energy storage applications. Nevertheless, the recoverable energy storage density (Wrec) still needs to be further improved to meet the requirements of the miniaturization and integration of pulsed power systems. In order to significantly increase Wrec, a strategy, by introducing A-site vacancies, stabilizing antiferroelectricity and decreasing the grain size, is proposed in this work. Here, Ag1−2xCaxNbO3 solid solutions were designed for achieving high maximum polarization (Pmax), large antiferroelectric–ferroelectric electric field (EF) and high breakdown electric field (Eb). A high Pmax of 39.6 μC cm−2, a large EF of 179 kV cm−1 and an Eb of 220 kV cm−1 were achieved in Ag0.92Ca0.04NbO3 ceramics, leading to an ultrahigh Wrec of 3.55 J cm−3. The significantly improved Wrec is about 2 times as high as that of the pure AgNbO3 counterpart. Meanwhile, the Ag0.92Ca0.04NbO3 ceramics exhibited temperature-insensitive Wrec with minimal variation less than 1.5% from room temperature up to 100 °C. A Ginzburg–Landau–Devonshire (GLD) phenomenology was proposed to reveal the increased stability of antiferroelectricity and the temperature-insensitive Wrec, which suggested that they are closely associated with the tailoring of free energy barriers for antiferroelectric–ferroelectric phase transition. The excellent energy storage performance makes the Ag1−2xCaxNbO3 system a good candidate for advanced pulsed power capacitors. More importantly, our findings open a new way for developing high performance AgNbO3-based and other lead-free systems for energy storage.

Thermo-sensitive luminescence of lanthanide complexes, clusters, coordination polymers and metal–organic frameworks with organic photosensitizers

Abstract: Luminescent lanthanide(III) complexes show narrow emission bands (full widths at half maximum < 10 nm in the visible region) based on 4f–4f transitions, which are suitable for application in displays and sensing devices. The temperature-dependent luminescence of lanthanide complexes is expected to be applied to effective temperature-sensitive paints with higher sensitivity over a wide range for measurements of the physical parameters of a material surface in the fields of fluid dynamics, aeronautical engineering, environmental engineering, and energy technology. In this review, the characteristic emissions of lanthanide ions, suitable detection systems for thermo-sensing properties, temperature dependent luminescence of lanthanide mononuclear complexes, polynuclear clusters, coordination polymers (CPs) and metal–organic frameworks (MOFs) are introduced. The theoretical considerations of their temperature-dependent photophysical processes and advanced ratiometric sensing systems for precise temperature detection are also described. Studies on luminescent lanthanide complexes with thermo-sensing properties open up the frontier field of research in advanced materials chemistry.

Smart strain sensing organic–inorganic hybrid hydrogels with nano barium ferrite as the cross-linker

Abstract: Regarding artificial intelligence and wearable soft electronics, increasing attention has been dedicated to hydrogel strain sensors. However, traditional hydrogels are insulating and fragile. To obtain a continuous and repeatable electrical signal output upon external stress or strain in a hydrogel, the combination of good mechanical property, good elasticity and high electrical conductivity is demanded. In order to apply hydrogel in the strain sensing field, in this work, a smart, flexible organic–inorganic polyanion polyacrylic acid (PAA) hybrid hydrogel is designed with nano barium ferrite (BaFe12O19) as a cross-linker without the addition of any chemically covalent or ionic cross-linkers, exhibiting a high ionic conductivity of 1.22 × 10−2 S cm−1. Due to high porosity as confirmed by scanning electron microscope (SEM), the BaFe12O19/PAA hybrid hydrogel demonstrates 100% recoverability and stable piezoresistive sensing performance with negligible hysteresis loops under cyclic compression loading tests compared with the N,N′-methylene bisacrylamide chemically cross-linked PAA hydrogel. This demonstrates that the BaFe12O19/PAA hydrogel is not only favorable to be used as a candidate for strain sensors in soft electronics but also facilitates the evolution of a new generation of flexible, wearable, and human-friendly intelligent devices.

Bi0.5Na0.5TiO3-based relaxor ferroelectric ceramic with large energy density and high efficiency under a moderate electric field

Abstract: Lead-free relaxor ferroelectric ceramics of (1 − x)(0.6Bi0.5Na0.5TiO3–0.4Sr0.7Bi0.2TiO3)–xAgNbO3 were fabricated by a conventional mixed oxide route. The multifunction of AgNbO3 (AN) doping into the 0.6Bi0.5Na0.5TiO3–0.4Sr0.7Bi0.2TiO3 (BNT–SBT) matrix can be divided into two main aspects. First, it enhances the breakdown electric field (Eb) as a result of reduced grain size and increased resistivity. Second, it improves η via enhancing the relaxation behavior and stabilizing the antiferroelectric (AFE) phase. Eventually, we achieved a large Wrec of 3.62 J cm−3 and a high η of 89% simultaneously under a moderate electric field of 246 kV cm−1 as the doping ratio x of AgNbO3 equals 0.05. In addition, the same sample also exhibits excellent temperature stability and good frequency stability, suggesting that AgNbO3 doped BNT–SBT ceramics could be an ideal candidate in high energy storage capacitors.