Search

White light-emitting diodes (WLEDs) hold great promise in lighting, display, and visible light communication devices, and single-component white emission carbon quantum dots (SCWE-CQDs) as the key component of WLEDs have many outstanding advantages. However, rapid and efficient synthesis of SCWE-CQDs with high photoluminescence quantum yield (PLQY) and stability remains challenging. Here, we report a novel solvent engineering strategy to obtain highly photoluminescent SCWE-CQDs by controlling the dilution ratios between N,N-dimethylformamide (DMF) and pristine red carbon quantum dots (RCQDs) solution. By optimizing synthesis conditions, the relative PLQY of the SCWE-CQDs solution reached 53%. Morphological, structural, and optical property characterizations indicate that the combined action of the hydrogen bond (HB) effect and the size effect leads to the blue shift of RCQDs, but the HB effect is more dominant than the particle size in causing large spectral shifts. In addition, the WLEDs with high color rendering index of 89 and remarkable reliability were obtained based on the highly photoluminescent SCWE-CQDs. This facile solvent engineering approach for synthesizing tunable emission CQDs will promote the progress of carbon-based luminescent materials for applications in optoelectronic devices.

Supplementary Material

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.

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.

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.

In this work, we report a polar-solvent-free, low-cost, and environmentally friendly method for synthesizing highly stable all-inorganic CsPbBr3 nanocrystals (NCs). Their shape and size are control...

Quantum dots (QDs) show a great potential for light-emitting diodes (LEDs) packaging, which still face great challenges compared with the matured phosphor downconversion materials. These are probably caused by the unique scattering and absorption properties of QDs, which are extremely different to the traditional phosphor due to their several nanometers size, while their effect on QDs-converted LEDs (QCLEDs) is barely studied. In this paper, we have experimentally and theoretically investigated the effect of scattering and absorption of CdSe/ZnS QDs on the optical performance for QCLEDs by comparing with the traditional yttrium aluminum garnet phosphor. Results indicate that the strong absorption (reabsorption) of QDs causes low radiant efficacy and stability for QCLEDs; their weak scattering also leads to a low color uniformity. It demonstrates that their unique scattering and absorption properties are key factors leading to low optical performance of QCLEDs compared with the traditional phosphor-converted LEDs. For purpose of gaining the white LED with high efficiency and stability, it is highly suggested to use a low QD concentration to reduce the reabsorption loss and the total internal reflection loss. We believe that this paper can provide a better understanding of improving the optical performance for QCLEDs from the prospective of scattering and absorption. In the future, it is important to use low QD concentration to gain high-performance white LEDs with high downconversion efficiency by optimizing packaging structures.

A rapid synthetic method for highly photoluminescent (PL) nitrogen-doped carbon quantum dots (N-CQDs) was developed by using a microreactor with foamy copper having different porosities. By taking advantage of the foamy copper, we obtained a high quantum yield (QY) of 84.1%, which was more efficient than most of the previous reports. Compared to the procedure without adding foamy copper, the QY when foamy copper was used was two times higher. The formation mechanism of the N-CQDs, which involved molecular condensation and the formation of carbon cores, was demonstrated. To explore the relationship between the use of a microreactor with foamy copper having different porosities and the PL properties of the N-CQDs, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis was employed. The results show that the surface functional groups and elemental contents influence the PL emission. We further demonstrate the application of the N-CQDs as probes for heavy metal ion detection. The results indicated that N-CQDs are very suitable for use as nanoprobes for Hg2+ ion detection and that the lowest detection limit (LOD) for Hg2+ is 2.104 nM, which is superior to many other research studies. This method highlights that the value of microreactor synthetic system as a tool for the environmental and hazard detection.

We demonstrate an organic macromolecule-assisted anion-exchange reaction method for tuning the emission spectrum of cesium lead halide perovskite (CsPbX3) nanocrystals (NCs) from green to near-ultraviolet using a microreactor. Using poly(lactic acid) (PLA), the emission peak of CsPbX3 NCs can be tuned from 514 nm to 420 nm while maintaining high photoluminescence (PL) quantum yields (QYs) of 33–90%. By taking advantage of the microreactor, we synthesize parent CsPbBr3 NCs and complete anion-exchange reactions at the same time, which is more efficient than most previously reported methods. The stability of CsPbX3 NCs is improved by PLA coating, especially for CsPbCl3, which shows long-term stability under ambient conditions for at least two weeks. The CsPbBr3 NCs are utilized with a red phosphor on a blue light emitting-diode (LED) chip, achieving white light emission with a luminous efficacy of 62.93 lm W−1 under a 20 mA driving current. Highly efficient white LEDs (wLEDs) demonstrate the potential of halide perovskite NCs for optoelectronic applications, including low-cost displays, lighting, and optical communication.

ZnO nanoparticles were incorporated into quantum dot (QD)-silicone encapsulation materials of the light-emitting diodes (LEDs) to exploit their strong scattering effect, which were proved by the ZnO-only film experiment. The novel packaging scheme led to a decrease in the radiation flux because of the conversion-energy loss of QDs and backscattering of ZnO nanoparticles. Under the similar color coordinate, the luminous flux of the ZnO-incorporated QD-LED showed a 3.37% increase compared to the conventional structure. This was attributed to the scattering effect, which enhanced the utilization of blue light and the conversion of yellow light. And the angular-dependent correlated color temperature (CCT) deviation was reduced from 862 to 712 K in the range of −70° to 70°. Moreover, the CCT monotonically decreased, and the chromaticity coordinate steadily shifted to the yellow region as the amount of ZnO nanoparticles increased. Therefore, ZnO nanoparticles can be a favorable optical performance enhancer for the future generation of QD-converted LEDs.

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 5 min, 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 Fe 3 + ion detection, and the lowest detection limit for Fe 3 + is 0.239 μM, 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.

We examined light-emitting diodes (LEDs) packaged with silicone encapsulation of carbon dots (CDs) that is doped using TiO2 nanoparticles (TiO2NPs). The results reveal that the adjustable emission spectra in a wide wavelength range (peak wavelength varies from ∼430 to ∼600 nm) can be obtained by controlling the amount of TiO2NPs for CDs embedded in the silicone encapsulant, and that the various colors of LEDs can be produced using CDs at a concentration of 10 wt%. Moreover, the luminous intensity can be increased by 31% at a TiO2NPs concentration of 0.05 wt%. These optical characteristics of CDs-based LEDs emerge from the enhanced light scattering ability of TiO2NPs, which increases the light reabsorption and extraction probability. Therefore, the proposed method has great potential for achieving low-cost and high-performance CDs-based LEDs for particular applications.

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.

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 ∼ 200 n m feature a broadband reflectance of ∼ 71 % at a thickness of 16 µm and are measured to have a transport mean free path of ∼ 3 µ m . The porous films with high reflectivity enable the application on light-emitting diodes and have great potential in other similar optoelectronic fields.

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 &deg, 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.

The ability to be mixed with the polymers is very important for applications of perovskite quantum dots (QDs), such as in display, lighting and so on. Here, a method for fabricating a thin film composed of CsPbBr 3 QDs and polydimethylsiloxane (PDMS) was reported. By using the ethyl acetate, a large number of ligands on the surface were removed and the combination with polymers can realize. Based on the thin film, an LED device was assembled and its luminous flux, luminous efficiency, color temperature and CIE color coordinates were measured. What’s more, the thin film revealed a splendid stability after being stored for 42 days without any protection, which show the broad prospects of it.

Low-dimensional materials attract much attention because of their unique and outstanding properties in optical and electronic products, giving a promising class of materials for optoelectronic applications. A facile synthesis method of CsPbBr3 nanorods (NRs) was presented in this paper. The nanorods have a one-dimensional (1D) scale, a high photoluminescence quantum yield (PLQY, 60%) and a narrow FWHM. By tuning the ratio of organic ligands, the CsPbBr3 NRs with the diameter of less than 20 nm and length up to several hundred nanometers were obtained. Moreover, because of the quantum confinement effects, a large blue-shift have happened in PL spectra. A light-emitting diode (LED) device was fabricated with our synthesized CsPbBr3 NRs. The LED device showed a strong green emission. All of these shows the ability of halide perovskite nanocrystals for applications on photoelectron, such as optical communication, display, lightning and so on.

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 &mu, M 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.

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.

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.