Precise regulation of the multicolor spectrum of carbon dots based on the bionic leaf vein ultrasonic microreactor.

Carbon dots (CDs) are a fascinating new type of fluorescent carbon nanomaterial with excellent photoelectric properties. However, preparing long-wavelength and multicolor-emitting CDs has been challenging, limiting their large-scale applications. Fortunately, a new efficient method has been proposed to co-regulate CDs' multicolor spectra using an ultrasonic microreactor. Inspired by plant leaves, a bionic vein microchannel was designed with good fluidity and high energy transfer efficiency. The optimal microchannel structural parameters were determined after investigating the effects of fractal angle, depth-to-width ratio, and inlet angle on the flow uniformity of the microchannel using numerical simulations. The efficiency of ultrasonic energy transfer was improved by directly coupling the microreactor and the sandwich transducer to fabricate the ultrasonic microreactor. Simulation results showed that the ultrasonic microreactor's vibration resonated along the longitudinal direction, and the ultrasonic intensity of the microreactor was maximal and uniform. A high-efficiency and controllable ultrasonic microreactor system was built to synthesize the CDs in situ. The influence of the ultrasound field intensity on CDs' preparation in a microreactor was simultaneously investigated to verify the ultrasound enhancement, and the PLQY of the high-performance CDs was found to be 83.1%. The CDs' multicolor spectra from the blue to the red region can be precisely tuned by adjusting key reaction parameters such as reaction temperature, flow rate, and precursor concentration. This new method shows promising applications in lighting, display, and other fields, making CDs a versatile and exciting new material to explore.

Multi-Objective Optimization of Liquid Silica Array Lenses Based on Latin Hypercube Sampling and Constrained Generative Inverse Design Networks.

Injection molding process parameters have a great impact on plastic production quality, manufacturing cost, and molding efficiency. This study proposes to apply the method of Latin hypercube sampling, and to combine the response surface model and "Constraint Generation Inverse Design Network (CGIDN)" to achieve multi-objective optimization of the injection process, shorten the time to find the optimal process parameters, and improve the production efficiency of plastic parts. Taking the LSR lens array of automotive LED lights as the research object, the residual stress and volume shrinkage were taken as the optimization objectives, and the filling time, melt temperature, maturation time, and maturation pressure were taken as the influencing factors to obtain the optimization target values, and the response surface models between the volume shrinkage rate and the influencing factors were established. Based on the "Constraint-Generated Inverse Design Network", the optimization was independently sought within the set parameters to obtain the optimal combination of process parameters to meet the injection molding quality of plastic parts. The results showed that the optimal residual stress value and volume shrinkage rate were 11.96 MPa and 4.88%, respectively, in the data set of 20 Latin test samples obtained based on Latin hypercube sampling, and the optimal residual stress value and volume shrinkage rate were 8.47 MPa and 2.83%, respectively, after optimization by the CGIDN method. The optimal process parameters obtained by CGIDN optimization were a melt temperature of 30 °C, filling time of 2.5 s, maturation pressure of 40 MPa, and maturation time of 15 s. The optimization results were obvious and showed the feasibility of the data-driven injection molding process optimization method based on the combination of Latin hypercube sampling and CGIDN.

Highly Stable and Photoluminescent CsPbBr3/Cs4PbBr6 Composites for White-Light-Emitting Diodes and Visible Light Communication.

Inorganic lead halide perovskite is one of the most excellent fluorescent materials, and it plays an essential role in high-definition display and visible light communication (VLC). Its photochromic properties and stability determine the final performance of light-emitting devices. However, efficiently synthesizing perovskite with high quality and stability remains a significant challenge. Here, we develop a facile and environmentally friendly method for preparing high-stability and strong-emission CsPbBr3/Cs4PbBr6 composites using ultrasonication and liquid paraffin. Tuning the contents of liquid paraffin, bright-emission CsPbBr3/Cs4PbBr6 composite powders with a maximum PLQY of 74% were achieved. Thanks to the protection of the Cs4PbBr6 matrix and liquid paraffin, the photostability, thermostability, and polar solvent stability of CsPbBr3/Cs4PbBr6-LP are significantly improved compared to CsPbBr3 quantum dots and CsPbBr3/Cs4PbBr6 composites that were prepared without liquid paraffin. Moreover, the fabricated CsPbBr3/Cs4PbBr6-LP-based WLEDs show excellent luminescent performance with a power efficiency of 129.5 lm/W and a wide color gamut, with 121% of the NTSC and 94% of the Rec. 2020, demonstrating a promising candidate for displays. In addition, the CsPbBr3/Cs4PbBr6-LP-based WLEDs were also demonstrated in a VLC system. The results suggested the great potential of these high-performance WLEDs as an excitation light source to achieve VLC.

Highly emissive green CsPbBr3/Cs4PbBr6 composites: formation kinetics, excellent heat, light, and polar solvent resistance, and flexible light-emitting application.

Benefit from their near-unity photoluminescence quantum yield (PL QY), narrow emission band, and widely tunable bandgap, metal halide perovskites have shown promising in light-emitting applications. Despite such promise, how to facile, environmentally-friendly, and large-scale prepare solid metal halide perovskite with high emission and stability remains a challenging. Herein, we demonstrate a convenient and environmentally-friendly method for the mass synthesis of solid CsPbBr3/Cs4PbBr6 composites using high-power ultrasonication. Adjusting key experimental parameters, bright emitting CsPbBr3/Cs4PbBr6 solids with a maximum PL QY of 71% were obtained within 30 min. XRD, SEM, TEM, Abs/PL, XPS, and lifetime characterizations provide solid evidence for forming CsPbBr3/Cs4PbBr6 composites. Taking advantage of these composites, the photostability, thermostability, and polar solvent stability of CsPbBr3/Cs4PbBr6 are much improved compared to CsPbBr3. We further demonstrated CsPbBr3/Cs4PbBr6 use in flexible/stretchable film and high-power WLEDs. After being subjected to bending, folding, and twisting, the film retains its bright emission and exhibits good resistance to mechanical deformation. Additionally, our WLEDs display a superior, durable high-power-driving capability, operating currents up to 300 mA and maintaining high luminous intensity for 50 hours. Such highly emissive and stable metal halide perovskites make them promising for solid-state lighting, lasing, and flexible/stretchable display device applications.

Multicolor Luminescent Carbon Dots: Tunable Photoluminescence, Excellent Stability, and Their Application in Light-Emitting Diodes.

Carbon dots (CDs) are attracting much interest due to their excellent photoelectric properties and wide range of potential applications. However, it is still a challenge to regulate their bandgap emissions to achieve full-color CDs with high emissions. Herein, we propose an approach for producing full-color emissive CDs by employing a solvent engineering strategy. By only tuning the volume ratio of water and dimethylformamide (H2O/DMF), the photoluminescence (PL) emission wavelengths of the CDs can be changed from 451 to 654 nm. Different fluorescence features of multicolor CDs were systematically investigated. XRD, SEM, TEM, Abs/PL/PLE, XPS, and PL decay lifetime characterizations provided conclusive evidence supporting the extent to which the solvent controlled the dehydration and carbonization processes of the precursors, leading to a variation in their emission color from red to blue. The as-prepared CDs exhibited excellent and stable fluorescence performance even after being heated at 80 °C for 48 h and with UV light continuously irradiated for 15 h. Based on their excellent fluorescent properties and photothermal stability, bright multicolor light-emitting diodes with a high CRI of up to 91 were obtained. We anticipate that these full-color emissive CDs are beneficial for applications in lighting, display, and other fields.

Optical Penetration and "Fingerprinting" Analysis of Automotive Optical Liquid Silicone Components Based on Wavelet Analysis and Multiple Recognizable Performance Evaluation.

The residual stress phenomenon in the injection process of an optical lens affects the quality of optical components, and the refractive error caused by geometric errors is the most serious, followed by the degradation of the accuracy and function of optical components. It is very important to ensure that the lens geometry remains intact and the refractive index is low. Therefore, a parameter design method for an optical liquid silicon injection molding was proposed in this study. Wavelet analysis was applied to the noise reduction and feature extraction of the cavity pressure/pressure retaining curve of the injection molding machine, and multiple identifiable performance evaluation methods were used to identify and optimize the parameters of the molding process. Taking an automotive LED lens as an example, Moldex3D simulation software was used to simulate the molding of an LED lens made of LSR material, and two key injection molding factors, melt temperature and V/P switching point, were analyzed and optimized. In this paper, the transmittance and volume shrinkage of LED lenses are taken as quality indexes, and parameters are optimized by setting different V/P switching points and melt temperature schemes. The experimental results show that the residual stress is negatively correlated with transmittance, and the higher the residual stress, the lower the transmittance. Under the optimum process parameters generated by this method, the residual stress of plastic parts is significantly optimized, and the optimization rate is above 15%. In addition, when the V/P switching point is 98 and the melt temperature is 30 °C, the product quality is the best, the volume shrinkage rate is the smallest, and the size is 2.895%, which also means that the carbon emissions are the lowest.

Numerical study on the scattering property of porous polymer structures via supercritical CO2 microcellular foaming.

Disordered porous polymer structures have gained tremendous attention due to their wide applications in various fields. As a simple yet versatile technique, supercritical CO2 microcellular foaming has been proposed to fabricate highly scattering porous polymer films, which have been used to enhance the efficiency of quantum dots (QDs) films. In the foaming process, numerous enclosed pores are generated, which induce significant scattering, underpinning the efficiency enhancement in optoelectronic devices. However, the scattering property of foamed porous structures has still not been well investigated, and effective guidelines for engineering the porous structures are still not available. In this work, we use Mie scattering theory and ray-tracing simulation to analyze the optical property of a single pore, pore assembly, and porous film. Furthermore, it is demonstrated that the scattering scheme in the porous QD films leads to a large enhancement of excitation light absorption and QD emission extraction. It is envisioned that our work will contribute to the engineering guidelines of porous structures and boost the application of porous structures in similar fields.

Bioinspired high-scattering polymer films fabricated by polymerization-induced phase separation.

Inspired by the porous scale of the bright white beetle Cyphochilus, a polymerization-induced phase separation method is proposed to fabricate bioinspired high-scattering polymer films with porous structures. With an optimized formulation, the porous films with a mean pore size of ∼200nm feature a broadband reflectance of ∼71% at a thickness of 16 µm and are measured to have a transport mean free path of ∼3µm. The porous films with high reflectivity enable the application on light-emitting diodes and have great potential in other similar optoelectronic fields.

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.

Ultrasonication-assisted synthesis of CsPbBr3 and Cs4PbBr6 perovskite nanocrystals and their reversible transformation.

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.

Investigating the transformation of CsPbBr3 nanocrystals into highly stable CsPbBr3/Cs4PbBr6 nanocrystals using ethyl acetate in a microchannel reactor.

The nanocrystals (NCs) of inorganic perovskites CsPbX3 and Cs4PbX6 (X = Cl, Br, I) are showing a great development potential due to their versatility of crystal structure. Here, we used a microchannel reactor to synthesize both CsPbBr3 NCs (CsPbBr3 NCs) and Cs4PbBr6 NCs with embedded CsPbBr3 (CsPbBr3/Cs4PbBr6 NCs). Via speed control of the precursor, ligands around the surface of NCs were effectively regulated by ethyl acetate, allowing the transformation from CsPbBr3 NCs to CsPbBr3/Cs4PbBr6 NCs in a short time, an outstanding stability of NCs, and a better crosslinking between NCs and polymer for the application of LEDs. Without any protection, the CsPbBr3/Cs4PbBr6 NCs, with a production rate of 28 mg min-1, retain more than 90% of the PL intensity after 84 d. Finally, the CsPbBr3/Cs4PbBr6 NCs were used to produce an LED device, and a wide color gamut of 122.8% NTSC or 91.7% Rec 2020 was attained.

Synergistic Surface Passivation of CH3 NH3 PbBr3 Perovskite Quantum Dots with Phosphonic Acid and (3-Aminopropyl)triethoxysilane.

CH3 NH3 PbBr3 perovskite quantum dots (PQDs) are synthesized by using four different linear alkyl phosphonic acids (PAs) in conjunction with (3-aminopropyl)triethoxysilane (APTES) as capping ligands. The resultant PQDs are characterized by means of XRD, TEM, Raman spectroscopy, FTIR spectroscopy, UV/Vis, photoluminescence (PL), time-resolved PL, and X-ray photoelectron spectroscopy (XPS). PA chain length is shown to control the PQD size (ca. 2.9-4.2 nm) and excitonic absorption band positions (λ=488-525 nm), with shorter chain lengths corresponding to smaller sizes and bluer absorptions. All samples show a high PL quantum yield (ca. 46-83 %) and high PL stability; this is indicative of a low density of band gap trap states and effective surface passivation. Stability is higher for smaller PQDs; this is attributed to better passivation due to better solubility and less steric hindrance of the shorter PA ligands. Based on the FTIR, Raman, and XPS results, it is proposed that Pb2+ and CH3 NH3 + surface defects are passivated by R-PO3 2- or R-PO2 (OH)- , whereas Br- surface defects are passivated by R-NH3 + moieties. This study establishes the combination of PA and APTES ligands as a highly effective dual passivation system for the synergistic passivation of multiple surface defects of PQDs through primarily ionic bonding.

Investigation of stability and optical performance of quantum-dot-based LEDs with methyl-terminated-PDMS-based liquid-type packaging structure.

Although quantum dots (QDs) have a high quantum yield close to one in a solution, they exhibit low conversion efficiency in a solidification polymer matrix, which hampers the development of QD-based light-emitting diodes (LEDs) with high stability and optical performance. In this study, we proposed a methyl-terminated-polydimethylsiloxane-(PDMS)-based liquid-type packaging structure (LPS) to improve stability and optical performance of QD-based LEDs. Compared with the traditional ethylene-terminated-PDMS-based solid-type packaging structure, the LPS with an optimized kinematic viscosity of 10000 m2/s can provide higher stability and optical performances for QD-based LEDs, including total radiant power and luminous flux. Consequently, the proposed effective and simple strategy has great potential for illumination and display applications.

Highly Photoluminescent and Stable N-Doped Carbon Dots as Nanoprobes for Hg2+ Detection.

We developed a microreactor with porous copper fibers for synthesizing nitrogen-doped carbon dots (N-CDs) with a high stability and photoluminescence (PL) quantum yield (QY). By optimizing synthesis conditions, including the reaction temperature, flow rate, ethylenediamine dosage, and porosity of copper fibers, the N-CDs with a high PL QY of 73% were achieved. The PL QY of N-CDs was two times higher with copper fibers than without. The interrelations between the copper fibers with different porosities and the N-CDs were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier Transform infrared spectroscopy (FTIR). The results demonstrate that the elemental contents and surface functional groups of N-CDs are significantly influenced by the porosity of copper fibers. The N-CDs can be used to effectively and selectively detect Hg2+ ions with a good linear response in the 0~50 µM Hg2+ ions concentration range, and the lowest limit of detection (LOD) is 2.54 nM, suggesting that the N-CDs have great potential for applications in the fields of environmental and hazard detection. Further studies reveal that the different d orbital energy levels of Hg2+ compared to those of other metal ions can affect the efficiency of electron transfer and thereby result in their different response in fluorescence quenching towards N-CDs.

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.

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.

Butterfly-inspired micro-concavity array film for color conversion efficiency improvement of quantum-dot-based light-emitting diodes.

Inspired by the Papilio blumei butterfly, quantum-dot (QD) film coupled with micro-concavity array (MCA) films is proposed in this Letter to enhance color conversion efficiency (CCE) of QD-based light-emitting diodes (LEDs). The diameter, aspect ratio, and pitch of the MCA are optimized in the optical simulations. Both the simulation and experimental results show that the scattering and double reflection effects are the key to the CCE improvement of QD films. The results show that the CCEs are increased from 19.98% to 21.59% and 21.78% (350 mA) for single-sided microstructured QD film and double-sided microstructured QD film configurations, respectively. Overall, the MCA film is a promising solution to enhance the CCE of QD-based LEDs.

Highly reflective nanofiber films based on electrospinning and their application on color uniformity and luminous efficacy improvement of white light-emitting diodes.

Based on electrospinning technology, in this study, we fabricated poly(lactic-co-glycolic acid) (PLGA) nanofiber films with high reflectivity and scattering properties. Various films with different thicknesses and fiber diameters were fabricated by changing the electrospinning time and solution concentration, respectively. Detailed optical measurements demonstrate that the film reflectance and scattering ability increase with the thickness, whereas fiber diameter contributes little to both properties. With optimized film thickness and fiber diameter, nanofiber films feature whiteness with a reflectance of 98.8% compared to the BaSO4 white plate. Furthermore, when deposited on the reflector surface of a remote phosphor-converted light-emitting diode lamp, nanofiber films witness a correlated color temperature deviation decrease from 8880 K to 1407 K and a luminous efficiency improvement of 11.66% at 350 mA. Therefore, the nanofiber films can be applied in lighting systems as a highly reflective coating to improve their light efficacy and quality.

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.