High-Performance Bioinspired Hierarchical Microgroove Wick for Ceramic Vapor Chambers Achieved by Nanosecond Pulsed Lasers.

Directly integrating ceramic vapor chambers into the insulating substrate of semiconductor power devices is an effective approach to solve the problem of heat dissipation. Microgrooves that could be machined directly on the shell plate without contact thermal resistance and mechanical dislocation offer exciting opportunities to achieve high-performance ceramic vapor chambers. In this study, a bioinspired hierarchical microgroove wick (BHMW) containing low ribs via one-step nanosecond pulsed laser processing was developed, as inspired by the Sarracenia trichome. The superwicking behavior of microgrooves with different structural parameters was investigated using capillary rise tests and droplet-spreading experiments. The BHMW exhibited excellent capillary performance and anisotropic hemiwicking performance. At a laser scanning spacing of 30 µm, the BHMW achieved a capillary wicking height of 114 mm within 20 s. The optimized BHMW demonstrated a capillary parameter (ΔPc·K) and an anisotropic hemiwicking ratio of 4.46 × 10-7 N and 11.93, respectively, which were 1182 and 946% higher than references, as achieved through nanosecond pulsed laser texturing under identical parameters. This work not only develops a high-performance hierarchical alumina microgroove wick structure but also outlines design guidelines for high-performance ceramic vapor chambers for thermal management in semiconductor power devices.

Experimental Investigation on Ultra-Thin Vapor Chamber with Composite Wick for Electronics Thermal Management.

Ultra-thin vapor chambers (UTVCs) are widely used to cool high-power electronics due to their excellent thermal conductivity. In this study, a UTVC of 82 mm × 58 mm × 0.39 mm with composite wick was prepared. The composite wick is composed of two layers of copper mesh and multiple spiral-woven meshes (SWMs), and the composite wick was applied in UTVC to improve liquid replenishment performance and temperature uniformity. Furthermore, the thermal performance of UTVCs with different support column diameters, filling ratios (FRs), and SWM structures was experimentally studied. The results found that the equivalent thermal conductivity (ETC) decreases as the diameter of the support column increases; the UTVC with 0.5 mm support column diameter has the highest ETC, at 3473 W/(m·K). Then, the effect of FR on the heat transfer performance of UTVCs with SWM numbers of 0, 1, 2, and 3 (0 SWMs, 1 SWM, 2 SWMs, 3 SWMs) is consistent, the 30% FR UTVC with 3 SWMs having the highest ETC, at 3837 W/(m·K). Finally, the increased number of SWMs can significantly improve the ultimate power of the UTVCs, the UTVC with 3 SWMs having the highest ultimate power, at 26 W. The above experimental studies indicate that the designed and manufactured UTVCs have great potential advantages in thermal dissipation for electronics.

A Luminous Efficiency-Enhanced Laser Lighting Device with a Micro-Angle Tunable Filter to Recycle Unconverted Blue Laser Rays.

In this work, a phosphor converter with small thickness and low concentration, based on a micro-angle tunable tilted filter (ATFPC), was proposed for hybrid-type laser lighting devices to solve the problem of silicone phosphor converters' carbonizing under high-energy density. Taking advantage of the filter and the scattering characteristics of microphosphors, two luminous areas are generated on the converter. Compared with conventional phosphor converters (CPCs), the lighting effects of ATFPCs are adjustable using tilt angles. When the tilt angle of the micro filter is 20°, the luminous flux of the ATPFCs is increased by 11.5% at the same concentration; the maximum temperature (MT) of ATFPCs is reduced by 22.8% under the same luminous flux and the same correlated color temperature (CCT) 6500 K. This new type of lighting device provides an alternative way to improve the luminous flux and heat dissipation of laser lighting.

Research on Laser Illumination Based on Phosphor in Metal (PiM) by Utilizing the Boron Nitride-Coated Copper Foams.

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.

Phosphor-in-glass (PIG) converter sintered by a fast Joule heating process for high-power laser-driven white lighting.

Currently, laser-driven lighting based on phosphor-in-glass (PIG) has drawn much interest in solid state lighting due to its high electro-optical efficiency and high-power density. However, the fabrication of PIG requires expensive equipment, long sintering time, and high cost. In this work, we utilized a simple, fast, and high temperature Joule heating process to make phosphor-in-glass bulk sintered in less than 20 s, which greatly improved the production efficiency. The PIG converters sintered under different sintering temperatures were investigated experimentally. The optimized PIG converter exhibited high and robust luminous efficacy (164.24 lm/W), a high radiant flux, and a small CCT deviation at 3.00 W. Moreover, the optimized sample also showed high temperature resistance at 3.00 W, robust temperature management during normal working. These results indicated that the optimized PIG converter sintered by the Joule heating process could offer great potential for the application in high-power laser-driven white lighting.

Synthesis of Highly Photoluminescent All-Inorganic CsPbX3 Nanocrystals via Interfacial Anion Exchange Reactions.

All-inorganic cesium lead halide perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have attracted significant attention owing to their fascinating electronic and optical properties. However, researchers still face challenges to achieve highly stable and photoluminescent CsPbX3 NCs at room temperature by the direct-synthesis method. Herein, we synthesize CsPbX3 NCs by a facile and environmentally friendly method, which uses an aqueous solution of metal halides to react with Cs4PbBr6 NCs via interfacial anion exchange reactions and without applying any pretreatment. This method produces monodisperse and air-stable CsPbX3 NCs with tunable spectra covering the entire visible range, narrow photoluminescence emission bandwidth, and high photoluminescence quantum yield (PL QY, 80%). In addition, the chemical transformation mechanism between Cs4PbBr6 NCs and CsPbX3 NCs was investigated. The Cs4PbBr6 NCs were converted to CsPbBr3 NCs first by stripping CsBr, and then, the as-prepared CsPbBr3 NCs reacted with metal halides to form CsPbX3 NCs. This work takes advantage of the chemical transformation mechanism of Cs4PbBr6 NCs and provides an efficient and environmentally friendly way to synthesize CsPbX3 NCs.

Effect of Excitation Wavelength on Optical Performances of Quantum-Dot-Converted Light-Emitting Diode.

Light-emitting diode (LED) combined with quantum dots (QDs) is an important candidate for next-generation high-quality semiconductor devices. However, the effect of the excitation wavelength on their optical performance has not been fully explored. In this study, green and red QDs are applied to LEDs of different excitation wavelengths from 365 to 455 nm. The blue light is recommended for exciting QDs from the perspective of energy utilization. However, QD LEDs excited at 365 nm have unique advantages in eliminating the original peaks from the LED chip. Moreover, the green or red light excited by ultraviolet light has an advantage in colorimetry. Even for the 455 nm LED with the highest QD concentration at 7.0 wt%, the color quality could not compete with the 365 nm LED with the lowest QD concentration at 0.2 wt%. A 117.5% (NTSC1953) color gamut could be obtained by the 365 nm-excited RGB system, which is 32.6% higher than by the 455 nm-excited solution, and this can help expand the color gamut of LED devices. Consequently, this study provides an understanding of the properties of QD-converted LEDs under different wavelength excitations, and offers a general guide to selecting a pumping source for QDs.

Improvement in Luminous Efficacy and Thermal Performance Using Quantum Dots Spherical Shell for White Light Emitting Diodes.

White light-emitting diodes (WLEDs) based on quantum dots (QDs) are gaining increasing attention due to their excellent color quality. QDs films with planar structure are universally applied in WLEDs for color conversion, while they still face great challenges in high light extraction and thermal stability. In this study, a QDs film with a spherical shell structure was proposed to improve the optical and thermal performance for WLEDs. Compared with the conventional planar structure, the luminous efficacy of the QDs spherical shell structure is improved by 12.9% due to the reduced total reflection effect, and the angular-dependent correlated color temperature deviation is decreased from 2642 to 283 K. Moreover, the highest temperature of the WLED using a QDs spherical shell is 4.8 °C lower than that of the conventional WLED with a planar structure, which is mainly attributed to larger heat dissipation area and separated heat source. Consequently, this QDs spherical shell structure demonstrates superior performance of QDs films for WLEDs applications.

Full spectral optical modeling of quantum-dot-converted elements for light-emitting diodes considering reabsorption and reemission effect.

Quantum dots (QDs) have attracted significant attention in light-emitting diode (LED) illumination and display applications, owing to their high quantum yield and unique spectral properties. However, an effective optical model of quantum-dot-converted elements (QDCEs) for (LEDs) that entirely considers the reabsorption and reemission effect is lacking. This suppresses the design of QDCE structures and further investigation of light-extraction/conversion mechanisms in QDCEs. In this paper, we proposed a full spectral optical modeling method for QDCEs packaged in LEDs, entirely considering the reabsorption and reemission effect, and its results are compared with traditional models without reabsorption or reemission. The comparisons indicate that the QDCE absorption loss of QD emission light is a major factor decreasing the radiant efficacy of LEDs, which should be considered when designing QDCE structures. According to the measurements of fabricated LEDs, only calculation results that entirely consider reabsorption and reemission show good agreement with experimental radiant efficacy, spectra, and peak wavelength at the same down-conversion efficiency. Consequently, it is highly expected that QDCE will be modeled considering the reabsorption and reemission events. This study provides a simple and effective modeling method for QDCEs, which shows great potential for their structure designs and fundamental investigations.

Regulating the Emission Spectrum of CsPbBr3 from Green to Blue via Controlling the Temperature and Velocity of Microchannel Reactor.

The ability to precisely obtain tunable spectrum of lead halide perovskite quantum dots (QDs) is very important for applications, such as in lighting and display. Herein, we report a microchannel reactor method for synthesis of CsPbBr3 QDs with tunable spectrum. By adjusting the temperature and velocity of the microchannel reactor, the emission peaks of CsPbBr3 QDs ranging from 520 nm to 430 nm were obtained, which is wider than that of QDs obtained in a traditional flask without changing halide component. The mechanism of photoluminescence (PL) spectral shift of CsPbBr3 QDs was investigated, the result shows that the supersaturation control enabled by the superior mass and heat transfer performance in the microchannel is the key to achieve the wide range of PL spectrum, with only a change in the setting of the temperature controller required. The wide spectrum of CsPbBr3 QDs can be applied to light-emitting diodes (LEDs), photoelectric sensors, lasers, etc.

Effect of flip-chip height on the optical performance of conformal white-light-emitting diodes.

To improve the optical performance of the conformal white light-emitting diodes (LEDs), previous studies mainly focus on the phosphor structures design by simulations and experiments methods. However, one of the most critical parameters, i.e., the height of chips, is barely studied. In this study, we have experimentally investigated the effect of the flip-chip height on the optical performance of conformal white LEDs. The results show that larger chip height can cause lower radiant power and luminous flux, while wider viewing angles can be achieved. By selecting a suitable chip height of 200 µm, superior color uniformity for white LEDs can be obtained with only 168 K correlated color temperature (ΔCCT). This study can provide a new perspective to improve the color uniformity without changing the phosphor structures or using special scattering elements; moreover, it can facilitate the selection of a proper chip height, considering different illumination requirements. Further investigations on the chip height considering packaging structures are still necessary to improve the luminous flux and the color uniformity simultaneously.

Efficient synthesis of highly fluorescent carbon dots by microreactor method and their application in Fe3+ ion detection.

Rapidly obtaining strong photoluminescence (PL) of carbon dots with high stability is crucial in all practical applications of carbon dots, such as cell imaging and biological detection. In this study, we proposed a rapid, continuous carbon dots synthesis technique by using a microreactor method. By taking advantage of the microreactor, we were able to rapidly synthesized CDs at a large scale in less than 5min, and a high quantum yield of 60.1% was achieved. This method is faster and more efficient than most of the previously reported methods. To explore the relationship between the microreactor structure and CDs PL properties, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were carried out. The results show the surface functional groups and element contents influence the PL emission. Subsequent ion detection experiments indicated that CDs are very suitable for use as nanoprobes for Fe3+ ion detection, and the lowest detection limit for Fe3+ is 0.239µM, which is superior to many other research studies. This rapid and simple synthesis method will not only aid the development of the quantum dots industrialization but also provide a powerful and portable tool for the rapid and continuous online synthesis of quantum dots supporting their application in cell imaging and safety detection.

Effect of ZnO nanostructures on the optical properties of white light-emitting diodes.

White light produced by blue LEDs with yellow phosphor is the most widely used methods, but it results in poor quality in angular CCT uniformity. In this work, a novel technique was introduced to solve this problem by integrating different ZnO nanostructures into white light-emitting diodes. The experiment of ZnO doped films and the simulation of Finite-Difference Time-Domain (FDTD) were carried out. The result indicated scattering effect of ZnO nanoparticles could improve uniformity of scattering energy effectively. Moreover, the effect of ZnO nanostructures on white light-emitting diodes (wLEDs) devices was also investigated. The CCT deviation of wLEDs devices would decrease from 3455.49 K to 96.30 K, 40.03 K and 60.09 K when the node-like (N-ZnO), sheet-like (S-ZnO) and rod-like ZnO (R-ZnO) respectively applied. The higher CCT uniformity and little luminous flux dropping were achieved when the optimal concentrations of N-ZnO, S-ZnO, and R-ZnO nanostructures were 0.25%, 0.75%, and 0.25%. This low-cost and green manufacturing method has a great impact on development of white light-emitting diodes.

The Effect of Supplementation of Long-Chain Polyunsaturated Fatty Acids During Lactation on Neurodevelopmental Outcomes of Preterm Infant From Infancy to School Age: A Systematic Review and Meta-analysis.

BACKGROUND AND OBJECTIVE: Long-chain polyunsaturated fatty acids, especially docosahexaenoic acid, have been suggested as a nutrition factor affecting visual and neurobehavioral development of preterm infants. Several randomized controlled trials (RCTs) have investigated the effect of supplementation of long-chain polyunsaturated fatty acids on preterm infants. We conducted a systematic review and meta-analysis to examine the efficacy of long-chain polyunsaturated fatty acid supplementation of formula or breast milk on the neurodevelopment outcomes of preterm infants. METHODS: Two authors searched PubMed and Cochrane Library (CENTRAL) for RCTs assessing efficacy of long-chain polyunsaturated fatty acids supplementation on the neurobehavioral and development outcomes of preterm infant. Human RCTs which supplemented long-chain polyunsaturated fatty acids during lactation and assessed neurodevelopment were included. The quality of each RCT was assessed, and the results of eligible trials were included in the systematic review and meta-analysis. RESULTS: We included 11 RCTs with 2272 total participants. Methodologic limitations existed to some extent in most RCTs that were included. Because the age of the participants from different trails was not the same, different scales and indexes had been assessed from different RCTs. Our meta-analysis indicated a significant effect of long-chain polyunsaturated fatty acids supplementation on the neurodevelopment of preterm infants assessed by the Mental Development Index of the Bayley Scales at one to three years of age versus the control groups. CONCLUSION: Analysis of our consolidated data indicates that long-chain fatty acid supplementation results in a significant improvement in the neurodevelopment of preterm infants as assessed by the Mental Development Index at one to three years of age. The available evidence suggests that long-chain polyunsaturated fatty acid supplementation during lactation may accelerate the pace of neurodevelopment in preterm infants, although their final developmental outcome may be unchanged.