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Most copper current collectors for commercial lithium-ion batteries (LIBs) are smooth copper foils, which cannot form a stable and effective combination with electrode slurry. They are likely to deform or fall off after long-term operation, resulting in a sharp decline in battery performance. What is worse is that this condition inevitably causes internal short circuits and thus brings about security risks. In this study, a process route of fabricating the functional surface structures on the surface of a copper collector for LIBs by twice-crisscross micro-plowing (TCMP) is proposed, which provides a new idea and an efficient method to solve the above problems from the perspective of manufacturing. The finite element simulation of TCMP combined with the cutting force test and morphological characterization is conducted to verify the forming mechanism of the surface structures on a copper sheet and its relationship with the processing parameters. The influence of several key processing parameters on the surface characteristics of the copper sheet is comprehensively explored. A series of functions is tested to obtain the optimal parameters for performance improvement of the current collector. Results show that the structured copper sheet with the cutting distance of 250 μm, cutting depth of 80 μm, and cutting crossing angle of 90° enables the best surface features of the current collector; the contact angle reaches 0°, the slurry retention rate is up to 89.2%, and the friction coefficient reaches 0.074. The battery using the as-prepared structured copper sheet as the current collector produces a specific capacity of 318.6 mAh/g after 50 cycles at a current density of 0.2 C, which is 132.7% higher than the one based on a smooth surface. The capacity reversibility of the sample with the new current collector is much better than that of the traditional samples, yielding a lower impedance.

Laser-driven illumination has unique advantages in high-power applications. Taking advantage of the valuable experience of light-emitting diodes (LED) development, phosphor in silicone (PiS) is considered to be one of the most potential commercial phosphor converter solutions for laser-driven illumination. However, the thermal quenching of the PiS converter is a bottleneck problem. Herein, a boron nitride (BN)-coated copper foam strategy is introduced for the laser-driven illumination system. The phosphor/silicone is embedded in the designed BN/copper foam to form a phosphor in metal (PiM) converter. Copper foam serves as an internal connected heat transfer channel; the BN coating solves the light absorption problem of the copper foam effectively. Based on this PiM(BN/copper foam) design, the heat dissipation is effectively improved. Under high-power laser excitation (8.13 W), the PiS converter cannot reach thermal equilibrium, and therefore the temperature increases sharply up to 660 °C. In comparison, the thermal performance of an optimized PiM(BN/copper foam) converter is able to maintain excellent stability, where the maximum temperature is only 166.5 °C. The proposed PiM strategy has a maximum temperature that is 493.5 °C lower than that of the reference PiS solution. Due to the superior thermal management, the luminous efficiency of the illumination system is constantly stable at 254 lm/W, though with less phosphor mass; and the related color temperature is about 6000 K all the time. This provides a practical and feasible heat-dissipation solution for high-power laser-driven illumination.

The correlated color temperature (CCT) variation of the phosphor-converted light-emitting diodes (LEDs) after curing is a common phenomenon. In the past, it was believed that the phenomenon was caused by the sedimentation of phosphor particles. However, not only sedimentation, but these particles can also flow with the natural convection of silicone because of nonuniform heating during curing. The convective flow of the phosphor particles during curing was studied in detail in this work. The CCT variation and phosphor particles flow in the LED device cup with different depths and wall inclination angles were studied. The results show that the CCT increases after curing when the depth of the device cup is shallow. The case is the opposite when the depth of the device cup is deep. The convective flow behaviors of the silicone were revealed in the simulation. The large-angle inclined wall can increase the silicone flow path length and inhibit the particles flow downward caused by the flow to a certain extent. It is envisioned that the findings will strengthen the understanding of the CCT variation phenomenon and guide the encapsulation structure design of LEDs for better color quality.

Self-accelerating beams have the unusual ability to remain diffraction-free while undergo the transverse shift during the free-space propagation. We theoretically identify that the transverse optical field distribution of 2D self-accelerating beam is determined by the selection of the transverse Cartesian coordinates, when the caustic method is utilized for its trajectory design. Based on the coordinate-rotation method, we experimentally demonstrate a scheme to flexibly manipulate the rotation of transverse optical field for 2D self-accelerating beams under the condition of a designated trajectory. With this scheme, the transverse optical field can be rotated within a range of 90 degrees, especially when the trajectory of 2D self-accelerating beams needs to be maintained for free-space photonic interconnection.

Visible light communication (VLC) is considered as a significant technology for new-generation communication. The VLC is supposed to provide high data rates and steady network links, which has high potential in dynamic wireless network transmission such as vehicle-to-vehicle communication. However, V2V network is always dynamic, which needs the receiver of the VLC system to have a large field of view (FOV) for stable networking. In this article, we proposed a sandwich structure light-trapping fluorescence antenna (LTFA). The LTFA consists of a short-wavelength pass long-wavelength reflect (SPLR) filter, a reflected mirror, and a 625-nm CdSe/ZnS quantum dots (QDs) fluorescent layer sandwiched between them. Multiple sets of variables of LTFA have been studied for optimization. A V2V VLC (V2V-VLC) system was built based on a commercial laser headlight. The FOV performance showed that a receiver with LTFA provides an incredible increment on receiving FOV, from 30° to 80°, while remaining considerable receiving signal power with an average optical gain of 1.6 for 80° FOV and an average optical gain of 10.45 for outer FOV. With the proposed LTFA, the average signal-to-noise ratio (SNR) of the V2V-VLC system can be improved 49% at 0°–80° and 123% at 30°–80°, respectively, showing promising communication performance.

Perovskite light emitting diodes (PeLEDs) have attracted considerable research attention because of their external quantum efficiency (EQE) of >20% and have potential scope for further improvement. However, compared to red and green PeLEDs, blue PeLEDs have not been extensively investigated, which limits their commercial applications in the fields of luminance and full-color displays. In this review, blue-PeLED-related research is categorized by the composition of perovskite. The main challenges and corresponding optimization strategies for perovskite films are summarized. Next, the novel strategies for the design of device structures of blue PeLEDs are reviewed from the perspective of transport layers and interfacial layers. Accordingly, future directions for blue PeLEDs are discussed. This review can be a guideline for optimizing perovskite film and device structure of blue PeLEDs, thereby enhancing their development and application scope.

In this study, we analyze the influence of the pore structure of an SBA-15 particle on the light emission from its inner adsorbed quantum dots (QDs) and outer light-emitting diode (LED) chips. It is found that the particle features of a high refractive index, comparable feature size of pore structure, and lower amount of QD adsorption help with QD light extraction, demonstrating a mechanism to suppress QD light propagating through pores and thus reducing the reabsorption loss. We consequently developed highly efficient QD white LEDs with wet-mixing QD/SBA-15 nanocomposite particles (NPs) by further optimizing the packaging methods and the introduced NP mass ratio. The LEDs demonstrated a record luminous efficacy (the ratio of luminous flux to electrical power) of 206.8 (entrusted test efficiency of 205.8 lm W-1 certificated by China National Accreditation Service) and 137.6 lm W-1 at 20 mA for white LEDs integrating only green QDs and green-red QD color convertors, respectively, with improved operating stability. These results are comparable to conventional phosphor-based white LEDs, which can be a starting point for white LEDs only using QDs as convertors toward commercialization in the near future.

Near-ultraviolet light-emitting diodes (NUV-LEDs) are more likely to be commercially fabricated. The improvement of their wall-plug efficiency (WPE) by facial and effective methods has made a great impact. We propose a highly reflective boron nitride silicone (BN/silicone) layer to improve the light output power for NUV-LEDs. Our results show that increasing the BN concentration contributes to a higher UV-reflectivity of the BN/silicone layers. When the BN concentration increases from 0.5 to 15 wt%, the light output power enhancement increases gradually, thus achieving a maximum light output power enhancement of 46.2% for NUV-LEDs at a driving current of 350 mA compared with pure silicone encapsulation devices. This significant improvement is attributed to the increased UV-reflectance by the polymer-based lead-frame and packaging materials. Furthermore, the emission angle is decreased by 7.8° at a BN concentration of 15 wt% at 350 mA owing to the strong scattering ability of the BN/silicone layer. This provides more concentrated energy in lighting applications.

Over the past decade, successive double-scratch tests have been extensively performed to study the grinding mechanism of brittle materials. However, the grits sometimes interact with the surface simultaneously. In this study, double tips with a tip separation of 0.6–1.8 μm are fabricated by focused ion beam. Subsequently, double-scratch tests on BK7 optical glass are conducted using the double-tip scratch tool with a scratch depth of 200–600 nm. The typical crack system and its evolution mechanism for double-tip scratch are discovered, before being explained using an analytical stress model. The ductile–brittle transition and the material-removal mechanism are discussed. An influential radius for the interference between cracks and the stress field in the double scratch is obtained, which can serve as a reference for the design of textured grinding wheels. Subsequently, the advantages and disadvantages of double-tip scratches are discussed considering different applications, such as microstructure fabrication and grinding.

Successive double scratch tests under the critical load of median crack initiation were conducted to investigate the crack behaviors under the influence of interaction between the arranged grits during grit-arranged grinding BK7 glass. After the inspection of the subsurface crack morphology by the advanced focused ion beam, it is found that with the separation distance increasing, the crack behaviors under the 2nd scratch experience three stages: a new type of crack—premature lateral crack initiation, no crack initiation and median crack reappearing. The crack behaviors that occurred in the former two stages can alleviate the subsurface damage. The initiation mechanisms of the unique crack behaviors were analyzed by a stress field analytical model. Also, the benefit of these unique crack behaviors on the grinding process was discussed.

Due to the demands of thermal performance enhancement of heat pipe solar collector, the fabrication of large-area flat heat pipes with the advantages of low cost and outstanding thermal performance has become more urgent. In this paper, a large-area ultra-thin flat heat pipe (LUFHP) with multiple parallel microchannels was fabricated by the aluminum extrusion process. Its total thickness is only 1.5 mm while the effective width is 170 mm. The effect of different filling ratios on the thermal performance was investigated under natural air convection and forced water cooling, respectively, including heat transport capability and thermal resistance. The experimental results indicate that the maximum heat transport capabilities for natural air convection and forced water cooling are 40 W with an optimal filling ratio of 25% and 25 W with an optimal filling ratio of 30%, respectively. The minimum total thermal resistances of the LUFHP are about 0.22 °C/W (natural air convection) and 0.73 °C/W (forced water cooling), which decrease by 74% and 57% compared with these of aluminum plate, respectively. That is, the proposed LUFHP shows better thermal performance under NAC for the replacement of aluminum plate in a wider range of heat load.

Deep ultraviolet light-emitting diodes (DUV-LEDs) have been considered as the most potential ultraviolet light sources, however, the traditional packaging with flat quartz glass has severe total internal reflection (TIR) loss, largely reducing the efficiency of DUV-LED. It is an efficient method to address this problem using organic lens, but traditional organic materials cannot be applied in DUV-LEDs because they are easily cracked by short-wave ultraviolet light. In this report, solid-liquid mixing state (SLMS) organic lens is proposed to enhance the light extraction efficiency and reliability of DUV-LEDs. Results show that the radiant power of DUV-LEDs using SLMS organic lens is enhanced by 53.86% under the injection current of 150 mA compared to DUV-LEDs (275nm)encapsulated with conventional flat quartz glass. Moreover, after 279 hours continuous operation, DUV-LEDs encapsulated with SLMS organice lens can still radiate 8.289 mW, which is only 3.94% lower than the initial power. Consequently, an efficient, low-cost and universal strategy has been proposed to enhance the light-extraction efficiency of DUV-LEDs, which has a great application prospect in packaging industry of DUV-LEDs.

Vertical-cavity surface-emitting laser (VCSEL) devices operate using a variety of viewing angles to satisfy the demands of different applications. One simple and universal approach to accomplish this is by using scattering elements in the packaging process for VCSEL chips. However, inevitable backward scattering loss is introduced, which suppresses the radiant efficacy of VCSEL devices. Therefore, we have proposed an enhanced specular reflection (ESR) structure with an opening circle window (OCW) to recycle the backward scattered light. The ray-tracing method is used to optimize the diameter of the OCW, as well as the thickness of the ESR structure. Furthermore, the light extraction mechanism is discussed. According to theoretical results, VCSEL devices with optimized ESR structures are fabricated and compared with traditional VCSEL devices. The experiment results demonstrate that ESR structures can significantly enhance the radiant efficacy of VCSEL devices using scattering elements. This shows great potential for applications involving illumination and 3-D imaging.

Ultrathin transition metal carbides with high capacity, high surface area, and high conductivity are a promising family of materials for applications from energy storage to catalysis. However, large-scale, cost-effective, and precursor-free methods to prepare ultrathin carbides are lacking. Here, we demonstrate a direct pattern method to manufacture ultrathin carbides (MoCx, WCx, and CoCx) on versatile substrates using a CO2 laser. The laser-sculptured polycrystalline carbides (macroporous, ~10–20 nm wall thickness, ~10 nm crystallinity) show high energy storage capability, hierarchical porous structure, and higher thermal resilience than MXenes and other laser-ablated carbon materials. A flexible supercapacitor made of MoCx demonstrates a wide temperature range (−50 to 300 °C). Furthermore, the sculptured microstructures endow the carbide network with enhanced visible light absorption, providing high solar energy harvesting efficiency (~72 %) for steam generation. The laser-based, scalable, resilient, and low-cost manufacturing process presents an approach for construction of carbides and their subsequent applications., Nature Communications, 10, ISSN:2041-1723

Quantum dot (QD) white light-emitting diodes (LEDs) are promising devices in illumination and display applications, and the low thermal stability of QDs is one of the biggest problems limiting their practical use. In this paper, we proposed a metal-based inverted packaging (MIP) structure to enhance the thermal performance and stability of QD white LEDs. The results indicate that the thermal power of LED chips can greatly increase the surface temperature of QD white LEDs, especially that of the color-converted layer and the base. Therefore, the LED chip was separated from the QD layer and isolated with low thermal conductivity layers of air and glass using the MIP structure. This successfully reduces the base temperature and constrains the thermal power of the LED chip on the upper phosphor layer, thus enhancing the thermal performance for the QD layer. Consequently, MIP-QD white LEDs have a small deviation of 57.3 K in their correlated color temperature (CCT) and a deviation of 0.29 in their color rendering index (CRI) at injection power values in a wide range of 0.08–1.3 W, with mean values of 4382 K and 90.3, respectively. Moreover, these devices have negligible reduction in their electroluminescence intensity, and CCT and CRI values after aging for 10 h under severe conditions at an injection power of 0.9 W. Consequently, this paper can provide a general guide to enhance the thermal performance and stability of QD white LEDs by separating the thermal power of the LED chip from the QD layer.

Crack initiation, propagation and interaction during single and double scratch testing are investigated at a constant load under different tool apex angles to understand the influence of tool apex angle on the material removal process of optical glass BK7. During the single scratch test, a large number of fragmentized and rambled shallow lateral cracks and radial cracks occur when the tool apex angle is small. As the tool apex angle increases, the number of shallow lateral cracks and radial cracks decreases, and the lateral cracks become more continuous. Radial cracks have curved paths under the surface and can lead to chippings independently. In addition, radial cracks can facilitate the deeper spreading of shallow lateral cracks. During the double scratch test, the interaction between radial cracks and the 2nd lateral cracks in the middle zone and three kinds of unique cracks, namely, extended lateral cracks, shallower 2nd lateral cracks and deeper radial cracks, are found when the tool apex angle and separation distance are both small. Finally, the material removal volume in the double scratch test is measured in terms of different tool apex angles and separation distances.

Quantum-dot (QD) white light-emitting diodes (LEDs) are promising for illumination and display applications due to their excellent color quality. Although they have a high quantum yield close to unity, the reabsorption of QD light leads to high conversion loss, significantly reducing the luminous efficacy and stability of QD white LEDs. In this report, SBA-15 mesoporous particles (MPs) with two-dimensional hexagonal pore structures (2D-HPS) are utilized to largely enhance the luminous efficacy and color-conversion efficiency of QD white LEDs in excess of 50%. The reduction in conversion loss also helps QD white LEDs to achieve a lifetime 1.9 times longer than that of LEDs using QD-only composites at harsh aging conditions. Simulation and testing results suggest that the waveguide effect of 2D-HPS helps in reducing the reabsorption loss by constraining the QD light inside the wall of 2D-HPS, decreasing the probability of being captured by QDs inside the hole of 2D-HPS. As such, materials and mechanisms like SBA-15 MPs with 2D-HPS could provide a new path to improve the photon management of QD light, comprehensively enhancing the performances of QD white LEDs.

With the rising development of the portable and wearable sensors and displays, the compact power source devices have become increasingly important and indispensable in our daily life. In this study, a flexible triboelectric nanogenerator (TENG), fabricated by the direct ink writing (DIW) method, has been proposed for the purpose of vibration energy harvesting to support power for these electronic devices. To strengthen the effective contact area of the opposite triboelectric polarities, the silicone elastomer, as viscoelastic inks, is extruded out directly onto the aluminum foil through the nozzle tip to construct the triboelectric patterns with rich and regular micro structures on the surface. Various film thickness, printing fibers spaces, contact frequencies, applied forces and printing paths are investigated to better understand the effects of the printing parameters in detail. The results show that the TENG can yield an output voltage of 124 V and the corresponding maximum power density of 608.5 mW/m2. Meanwhile, via vibration energy harvesting, the TENG is demonstrated to sustainably drive 51 LEDs and a 3-in. electrowetting display. Our work paves a new way for the individual design and digital manufacture of friction surface structures for the flexible, stretchable and wearable TENG.

We demonstrate an ultrasonication-assisted synthesis without polar solvent of CsPbBr3 and Cs4PbBr6 perovskite nanocrystals (PNCs) and their reversible transformation. The as-prepared CsPbBr3 PNCs and Cs4PbBr6 PNCs exhibit different optical properties that depend on their morphology, size, and structure. The photoluminescence (PL) emission and quantum yield (QY) of the CsPbBr3 PNCs can be tuned by changing the ultrasound power, radiation time, and the height of the vibrating spear. The optimized CsPbBr3 PNCs show a good stability and high PL QY of up to 85%. In addition, the phase transformation between CsPbBr3 PNCs and Cs4PbBr6 PNCs can be obtained through varying the amount of oleylamine (OAm) and water. The mechanism of this transformation between the CsPbBr3 PNCs and Cs4PbBr6 PNCs and their morphology change are studied, involving ions equilibrium, anisotropic growth kinetics, and CsBr-stripping process.

Quantum dots (QDs) attract great attention due to their narrow emission spectra, providing excellent light quality for light-emitting diodes (LEDs) in illumination and display applications. However, their low thermal reliability suppresses the commercial applications of QD-based LEDs. In this report, it is the first time that we realize high thermal performance and reliability QD-based LEDs with watt-level injection power. The QD-on-reflector (QOR) structure is proposed to separate QDs from the heat source of chips, and targeted cooling for QD/polymer composites is achieved with an Al-based reflector. Compared with the reference [conventional QD-on-chip (QOC) structures], the QOR-LEDs exhibit higher total radiant power/luminous flux and color consistency. Most important, the QOR-LED has a steady temperature of only approximately 50 °C in QD/polymer composites, which is 90 °C lower than the reference and is the reported lowest temperature for QD-based LEDs. The working-aging test shows that the luminous flux maintenance (LFM) factor of the QOR-LED is 92.2%, whereas that of the reference is only 21.2% after aging for 20 min. This corresponds to a lifetime of 88.5 times longer than that of the QOC-LED at the same LFM of 20%. Consequently, the QOR structure can provide better optical performance, superior thermal performance, and longer lifetime for QD-based LEDs.

Heat accumulation on phosphor converter is one of the most serious bottlenecks that impede the development of the laser illumination. In this work, a copper powder sintered flattened heat pipe coated with high reflectivity silver was utilized to dissipate the heat from the phosphor stimulated by three high power blue lasers (450 nm). In comparison, a conventional aluminum heat pipe with the same size of the heat pipe substrate was investigated either. The thermal and optical performances were experimentally evaluated. It was found that the heat pipe can lower the phosphor temperature and maintain the output radiant power constantly. Moreover, the heat pipe substrate can reduce the chromatic shift during the temperature rising. The correlated color temperature (CCT) deviation is only 292 K during a 1200 s measurement at an input current of 2.5 A. The highest driven power that the heat pipe substrate can sustain is 34.4 W, which is 14.7% higher than the aluminum substrate. In addition, the carbonization failure process of the phosphor and silicone mixture were revealed in this work. Some further research suggestions were also proposed on improving the thermal and optical performances of the laser illumination.

The inorganic halide perovskite quantum dots (QDs) have been considered as a promising substitute for white light-emitting diodes (WLEDs). In this paper, the green CsPbBr3 QDs and red K2SiF6:Mn4+ (KSF) phosphor were used to fabricate the conversion layers. Because the location of the layers is fundamental to the absorption priority of blue light, the location of KSF and QDs were controlled and the QDs-up type and QDs-down type WLEDs were made. The optical power, luminous efficiency, CCE, and luminous intensity in the middle of QDs-up type are 13.83 mW, 13.54 lm/W, 11.94%, and 2.65 cd, meaning 24.26%, 25.72%, 2.63%, and 23.83% higher than those of QDs-down type, respectively. In addition, the QDs-up type has a lower correlated color temperature (CCT) shift of 734 K and a decreased highest temperature of 56.8° (51.5% and 14.9% lower). These key property differences indicate that the QDs-up type is more suitable for the application in display and backlight. In order to explore the reasons for these differences, the emission spectra, CCE, reflection rate, absorption rate, and temperature curves of QDs or KSF films were also analyzed, which provided a better understanding of designing package structures.

Perovskite quantum dots (QDs) attracted a lot of attention recently due to their high light conversion efficiency, and high color purity. However, perovskite materials are sensitive to heat. High temperature will cause serious quenching problem of the perovskite QDs. In order to solve the QDs thermal quenching problem without destroying their optical characters. A circulating quantum dots colloidal solution converter (CQD-converter) was developed. A closed loop pump tube coated with Teflon was utilized to prevent perovskite QDs from the external environment. A peristaltic pump was utilized to drive the QDs colloidal solution through a Peltier cooler for dissipating the heat of the QDs colloidal solution. The lifetime of the perovskite QDs can be significantly improved under a 450nm laser excitation. The effects of temperature of the Peltier cooler and flow velocity on the optical properties of QDs were also investigated. Compared to the static quantum dots colloidal solution (SQD-converter), which quenched after 7 min, the optical properties were maintained after 600 min for the CQD-converter.

A novel composite heat pipe (CHP) that consists of a conventional heat pipe (HP) with a phase change material (PCM) storage chamber wrapped on the adiabatic section was proposed in this work. The CHP combines the advantages of the high thermal conductivity of HP and the high thermal storage capacity of the PCM. A measurement system was established to analyze the thermal performance with different effect factors of the CHP, including the filling rate of the PCM, heating power and wind speed. Multi-cycle transient thermal controlling performance was also investigated. Results show that the CHP can enhance the absorption-dissipation thermal performance, improve the isothermality, decrease the start-up temperature and greatly reduce the thermal shock in cyclic thermal scenarios. We believe that the CHP can be developed as high-potential heat-transfer medium for reliable thermal management.

Micro-scale patterned arrays and nano-scale rough morphology are promising for improving the light-extraction performance of GaN-based thin film light-emitting diodes (TFLEDs), while the light-extraction mechanisms of the multiscale architectures combining these two structures have not been investigated yet. In this report, we have adopted a pattern transfer and wet etching combined method to fabricate multiscale patterned arrays with rough morphology (msPARM) on n-GaN layers for TFLEDs and investigated their light-extraction mechanisms by the finite-difference time domain and ray-tracing combined method. The results show that the TFLEDs achieve the maximum radiant efficacy using the msPARM with an etching time of 8 min, which is increased by 16.3% and 1.7% compared with that achieved using only the patterned arrays or only the rough morphology, respectively. Most importantly, optical simulation reveals that the msPARM can provide a high transmittance for light with large emission angles from the active region using the inclined surface of micro-scale concave cones, while effectively suppressing the reflection loss for light with small emission angles using the scattering effect of nano-scale rough morphology, resulting in enhancing the light-extraction of the TFLEDs. Consequently, this study can provide a better understanding to design the multiscale structures for achieving high efficiency LEDs.