Efficiency enhancement of quantum dot-phosphor hybrid white-light-emitting diodes using a centrifugation-based quasi-horizontal separation structure.

In this paper, a centrifugation-based quasi-horizontal separation (c-HS) structure is proposed to enhance the QD light extraction of QD-phosphor hybrid white LEDs (WLEDs), effectively suppressing the backscattered loss from phosphor at the top region of the QD layer. Results indicate that a large centrifugation speed and dispensing mass of the QD layer is more beneficial to reducing the local density of phosphor at the top region, realizing quasi-horizontal separation between phosphor and QDs. Moreover, WLEDs with c-HS structure and conventional vertically layered packaging reference structure were compared at different correlated color temperatures (CCT). The radiant power and luminous flux achieved by the c-HS structure were 13.6% and 10.8%, respectively, higher than the reference structure at a typical warm white color of ∼4000 K. Consequently, this study can provide a new perspective on designing the separation structure for QD-phosphor hybrid WLEDs considering the backscattering loss of QD light.

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.

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.

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.

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.

Improving the optical performance of multi-chip LEDs by using patterned phosphor configurations.

In order to improve the color uniformity of multi-chip LEDs, a patterned phosphor configuration has been proposed by using pulsing spray process. The patterned phosphor has detached yellow and red phosphor regions matching every single LED chip. Optical performances of different phosphor parameters are experimentally investigated. The results show that the yellow central coating (YCC) configuration produces outstanding performance not only in chromatic uniformity but also in luminous. In comparison with the conventional phosphor coating, the YCC patterned phosphor LED can improve the luminous flux by 20.6%, and decrease the difference of the correlated color temperature (CCT) distribution from 1362K to 489K. We believe that the patterned phosphor configuration can be used for improving optical properties of multi-chip LEDs.

Enhancement of luminous efficacy for LED lamps by introducing polyacrylonitrile electrospinning nanofiber film.

Polyacrylonitrile electrospinning nanofiber film was introduced into a light emitting diode (LED) lamp to exploit the strong reflective and scattering effects. The light extraction mechanism was studied systematically for three different electrospinning types in three different types of LED lamps. For the all-electrospinning types, the luminous efficacy increased for the white LED, outwards remote phosphor layer, and inwards remote phosphor layer lamps by 10.98, 16.97, and 18.35%, respectively, compared with the reference lamp. Lamps with stronger backscatter had larger luminous efficacy enhancements. The reflector-electrospinning type helped redirect lights with large emission angles. The substrate-electrospinning type was beneficial for recycling the total interior reflection lights and increasing the yellow to blue ratio. Additionally, the all-electrospinning white LED lamps remains 97.89% luminous flux after a 96-hour aging process. Electrospinning fiber films are favorable luminous efficacy enhancers for the future generation of LED lamps.

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.

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.

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.

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.

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.

Color uniformity enhancement for COB WLEDs using a remote phosphor film with two freeform surfaces.

The color uniformity (CU) of chip-on-board (COB) white light emitting diodes (WLEDs) has been improved by using remote phosphor films with two freeform surfaces (TFS-RPFs). The finite-difference time-domain (FDTD), Monte Carlo ray-tracing, and color-thickness feedback (CTFB) methods were used to design the TFS-RPFs: the blue light distribution of COB WLEDs is greatly affected by the angular thickness distribution of TFS-RPFs, and a high CU can be achieved iteratively. The directional inconsistency of incident and emergent blue light, scattering effect of TFS-RPFs, and illumination characteristics of the COB source were also investigated. COB WLEDs containing optimized TFS-RPFs achieved high CU with a decrease of 26.2% in maximum CCT deviation; thus, TFS-RPFs can improve the CU of COB WLEDs.

CCT-tunable LED device with excellent ACU by using micro-structure array film.

We apply a microstructure array (MSA) film to improve the angular color uniformity (ACU) of a correlated-color-temperature-tunable LED (CCT-tunable LED) with tunable CCT ranging from 2700 to 6500 K. The effects of the MSA film area and the height between the film and LED are investigated and optimized. The resulting ACU is greatly improved for all CCT ranges with little luminous flux loss. For a typical CCT range of 3000-4000 K, with a full-covering MSA film and height H = 5 mm, the CCT deviation is significantly reduced from 1090 K to 218 K, with only 1.8% luminous flux loss.

Energy feedback freeform lenses for uniform illumination of extended light source LEDs.

Using freeform lenses to construct uniform illumination systems is important in light-emitting diode (LED) devices. In this paper, the energy feedback design is used for freeform lens (EFFL) constructions by solving a set of partial differential equations that describe the mapping relationships between the source and the illumination pattern. The simulation results show that the method can overcome the illumination deviation caused by the extended light source (ELS) problem. Furthermore, a uniformity of 95.6% is obtained for chip-on-board (COB) compact LED devices. As such, prototype LEDs manufactured with the proposed freeform lenses demonstrate significant improvements in luminous efficiency and emission uniformity.

Improving LED CCT uniformity using micropatterned films optimized by combining ray tracing and FDTD methods.

Although the light-emitting diode (LED) has revolutionized lighting, the non-uniformity of its correlated color temperature (CCT) still remains a major concern. In this context, to improve the light distribution performance of remote phosphor LED lamps, we employ a micropatterned array (MPA) optical film fabricated using a low-cost molding process. The parameters of the MPA, including different installation configurations, positioning, and diameters, are optimized by combining the finite-difference time-domain and ray-tracing methods. Results show that the sample with the upward-facing convex-cone MPA film that has a diameter of half of that of the remote phosphor glass, and is tightly affixed to the inward surface of the remote phosphor glass renders a superior light distribution performance. When compared with the case in which no MPA film is used, the deviation of the CCT distribution decreases from 1033 K to 223 K, and the corresponding output power of the sample is an acceptable level of 85.6%. We perform experiments to verify our simulation results, and the two sets of results exhibit a close agreement. We believe that our approach can be used to optimize MPA films for various lighting applications.

Carbon carrier-based rapid Joule heating technology: a review on the preparation and applications of functional nanomaterials.

Compared to conventional heating techniques, the carbon carrier-based rapid Joule heating (CJH) method is a new class of technologies that offer significantly higher heating rates and ultra-high temperatures. Over the past few decades, CJH technology has spawned several techniques with similar principles for different application scenarios, including ultra-fast high temperature sintering (UHS), carbon thermal shock (CTS), and flash Joule heating (FJH), which have been widely used in material preparation research studies. Functional nanomaterials are a popular direction of research today, mainly including nanometallic materials, nanosilica materials, nanoceramic materials and nanocarbon materials. These materials exhibit unique physical, chemical, and biological properties, including a high specific surface area, strength, thermal stability, and biocompatibility, making them ideal for diverse applications across various fields. The CJH method is a remarkable approach to producing functional nanomaterials that has attracted attention for its significant advantages. This paper aims to delve into the fundamental principles of CJH and elucidate the efficient preparation of functional nanomaterials with superior properties using this technique. The paper is organized into three sections, each dedicated to introducing the process and characteristics of CJH technology for the preparation of three distinct material types: carbon-based nanomaterials, inorganic non-metallic materials, and metallic materials. We discuss the distinctions and merits of the CJH method compared to alternative techniques in the preparation of these materials, along with a thorough examination of their properties. Furthermore, the potential applications of these materials are highlighted. In conclusion, this paper concludes with a discussion on the future research trends and development prospects of CJH technology.

Surface Treatment with Tailored π-Conjugated Fluorene Derivatives Significantly Enhances the Performance of Perovskite Light-Emitting Diodes.

Surface defect passivation and carrier injection regulation have emerged as effective strategies for enhancing the performance of perovskite light-emitting diodes (Pero-LEDs). It usually requires two functional molecules to realize defect passivation and carrier injection regulation separately. In other words, developing one single molecule possessing these capabilities remains challenging. Herein, we utilized π-conjugated fluorene derivatives as surface treatment materials, 9,9-Spirobi[fluorene] (SBF), 9,9-Spirobifluoren-2-yl-diphenylphosphine oxide (SPPO1), and 2,7-bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13), to investigate the influence of their chemical structure on device optoelectronic performance, especially for defect passivation and carrier injection regulation. Consequently, the passivation capability of double-bonded SPPO13 surpassed single-bonded SPPO1 and nonbonded SBF, which all showed excellent electron transport properties, enhancing electron injection. The maximum external quantum efficiencies (EQE) for Pero-LEDs treated with SBF, SPPO1, and SPPO13 were 8.13, 17.48, and 22.10%, respectively, exceeding that of the derivative-free device (6.55%). Notably, SPPO13-treated devices exhibited exceptional reproducibility, yielding an average EQE of 20.00 ± 1.10% based on 30 devices. This result emphasizes the potential of tailored fluorene derivatives for enhancing the device performance of Pero-LEDs.

A meta-analysis of internal mammary lymph node metastasis in breast cancer patients.

BACKGROUND: Knowing the status of the internal mammary lymph (IML) nodes is important for accurate staging and appropriate selection of subsequent treatment in breast cancer. We conducted a meta-analysis to clarify the rate of IML node metastasis in breast cancer patients and discussed the importance of this finding. METHODS: We retrieved articles from the literature that reported positive rates of IML node metastasis in breast cancer patients. The quality of the selected articles was assessed using the 'Methodological Index for Non-Randomized Studies'. The heterogeneity was tested, and publication bias was assessed using a funnel plot. Finally, the positive rate of IML node metastasis in breast cancer patients was calculated using the random-effects model. RESULTS: 15 articles met the inclusion criteria and a total of 4,248 patients were included in the analysis. Heterogeneity across the studies was statistically significant (p = 0.014); thus, the random-effects model was used and the calculated positive rate of IML node metastasis was 23% (95% confidence interval (CI), 0.21-0.25). CONCLUSIONS: Approximately 23% of the breast cancer patients had IML node metastases, for which the prognosis is generally poor. Accurate staging and integrated treatment are necessary to improve the survival of these patients.

Heavy metals distribution characteristics, source analysis, and risk evaluation of soils around mines, quarries, and other special areas in a region of northwestern Yunnan, China.

In this study, based on the assessment of soil heavy metals (HMs) pollution using relevant indices, a comprehensive approach combined network environ analysis (NEA), human health risk assessment (HHRA) method and positive definite matrix factor (PMF) model to quantify the risks among ecological communities in a special environment around mining area in northwest Yunnan, calculated the risk to human health caused by HMs in soil, and analyzed the pollution sources of HMs. The integrated risks for soil microorganisms, vegetations, herbivores, and carnivores were 2.336, 0.876, 0.114, and 0.082, respectively, indicating that soil microorganisms were the largest risk receptors. The total hazard indexes (HIT) for males, females, and children were 0.542, 0.591, and 1.970, respectively, revealing a relatively high and non-negligible non-carcinogenic risks (NCR) for children. The total cancer risks (TCR) for both females and children exceeded 1.00E-04, indicating that soil HMs posed carcinogenic risks (CR) to them. Comparatively, Pb was the high-risk metal, accounting for 53.76%, 57.90%, and 68.09% of HIT in males, females, and children, respectively. PMF analysis yielded five sources of pollution, F1 (industry), F2 (agriculture), F3 (domesticity), F4 (nature), and F5 (traffic).