High‐efficiency quantum dot light‐emitting diodes with blue cadmium‐free quantum dots

We report outstanding electroluminescence properties of high‐efficiency blue cadmium‐free quantum dot light‐emitting diodes (QD‐LED). External quantum efficiency (EQE) of 14.7% was achieved for QD‐LED emitting at 428 nm. Furthermore, we developed high‐efficiency and narrow wavelength emission zinc selenide (ZnSe) nanocrystals emitting at 445 nm and achieved QD‐LED with an EQE of 10.7%. These new QDs have great potential to be used in next‐generation QD‐LED display with wide color gamut.     

Monochromatic LEDs based on perovskite quantum dots: Opportunities and challenges

Perovskite quantum dots (QDs) are emerging as one of the most promising candidates for the monochromatic light‐emitting diodes (LEDs) approaching the Rec. 2020 color gamut due to their extremely narrow emission bandwidth. Another important aspect are the high photoluminescence quantum yield (PLQY) values that can be obtained either in solution or thin films making these materials as promising candidates for optoelectronic applications such as LEDs or solar cells. Considerable research efforts in chemistry, chemical engineering, solid‐state physics, and material sciences have been made in the past years. The new opportunity in the field of semiconductor quantum dots is still in the beginning phase and is expected to remain active in the following years. Here, in this invited commentary, we briefly discuss and summarize the opportunities and challenges in both fundamental and technological aspects, based on our work and the recent work in this field.     

All solution‐processed white quantum‐dot light‐emitting diodes with three‐unit tandem structure

Quantum‐dot light‐emitting diodes (QLEDs) are promising candidates for next generation displays. White QLEDs which can emit red, green and blue colors are particularly important; this is because the combination of white QLEDs and color filters offers a practical solution for high‐resolution full‐color displays. In this work, we demonstrate all‐solution processed three‐unit (red/green/blue) white tandem QLEDs for the first time. The white tandem devices are achieved by serially connecting the red bottom sub‐QLED, the green middle sub‐QLED and the blue top sub‐QLED using the inter‐connecting layer (ICL) based on ZnMgO/PEDOT:PSS heterojunction. With the proposed ICL, the two‐unit tandem QLEDs exhibit a high current efficiency of 22.22 cd/A, while the three‐unit white QLEDs exhibit evenly separated red, green and blue emission with a CIE coordinate of (0.30, 0.44), a peak current efficiency of 4.75 cd/A and a high luminance of 4206 cd/m². Displays based on the developed white QLEDs exhibit a wide color gamut of 114% NTSC. This work confirms the effectiveness of the proposed ZnMgO/PEDOT:PSS ICL and the feasibility of making all‐solution processed tandem white QLEDs by using the proposed ICL.     

Coaxial probe‐fed open‐ended waveguide antenna based on sand casting process with filtering characteristics and all‐in‐one structure

In this article, a coaxial probe‐fed open‐ended waveguide filtering antenna with all‐in‐one structure is proposed and fabricated by adopting sand casting process. It is known that for waveguide component with complex internal space, detached parts, and post‐processing assembly are often necessary, while unavoidably resulting in error, air gap and loss. In this context, sand casting process is here utilized to fabricate the whole waveguide structure directly, thus achieving a fully integrated antenna. Besides, by controlling the external couplings from probe feed and free space, the proposed coaxial probe‐fed antenna can provide similar impedance matching to a waveguide‐fed three‐order waveguide filter. Both the frequency‐ and time‐domain reflection coefficients of filter and antenna have been compared and analysed. An antenna prototype is fabricated and measured to validate the proposed design, which provides a successful example of all‐in‐one waveguide filtering antenna.     

Ten micrometer pixel,quantum dots color conversion layer for high resolution and full color active matrix micro‐LED display

A fine patternable quantum dots (QDs) color conversion layer (CCL) for high resolution and full color active matrix (AM) micro‐LED (μ‐LED) display is demonstrated. QDs CCL could be patterned until 10 μm using photolithography process. It is found that multicoatings with red and green QDs (R‐ and G‐QDs) CCLs on LED array can provide full color AM display.     

Flexible quantum dot light‐emitting devices for targeted photomedical applications

Quantum dot light‐emitting devices (QLEDs), originally developed for displays, were recently demonstrated to be promising light sources for various photomedical applications, including photodynamic therapy cancer cell treatment and photobimodulation cell metabolism enhancement. With exceptional emission wavelength tunability and potential flexibility, QLEDs could enable wearable, targeted photomedicine with maximized absorption of different medical photosensitizers. In this paper, we report, for the first time, the in vitro study to demonstrate that QLEDs‐based photodynamic therapy can effectively kill Methicillin‐resistant Staphylococcus aureus, an antibiotic‐resistant bacterium. We then present successful synthesis of highly efficient quantum dots with narrow spectra and specific peak wavelengths to match the absorption peaks of different photosensitizers for targeted photomedicine. Flexible QLEDs with a peak external quantum efficiency of 8.2% and a luminance of over 20,000 cd/m² at a low driving voltage of 6 V were achieved. The tunable, flexible QLEDs could be employed for oral cancer treatment or diabetic wound repairs in the near future. These results represent one fresh stride toward realizing QLEDs' long‐term goal to enable the wide clinical adoption of photomedicine.     

A Note on all‐Stabilizing Proportional Controllers for Single Input–Single Output Systems

This paper aims to present a practical technique for the synthesis of proportional controllers for continuous time control systems. This technique depends on the generalization of the Nyquist stability criterion and promises soft computing of the crossing direction of the diagram where the plot crosses the real axis on the complex plane.     

Microstrip stepped‐impedance ring all‐pass filter and wideband 90° phase shifter

A new all‐pass filter (APF) is proposed. The APF is based on a symmetrical ring, consisting of four sections of transmission line, which are identical in electrical length, different in characteristic impedance. Two input/output ports are connected orthogonally to the ring. The APF is analyzed by using the odd‐even model, and the all‐pass condition is then theoretically obtained. Meeting the condition, the circuit is all‐pass in frequency, but nonlinear in transmission phase. The nonlinear transmission phase with frequency may be adjusted by changing the lines' impedances, while remaining the all‐pass property. Then the APF is used to design a wideband 90° differential phase shifter with adjustable bandwidth. Samples are designed, fabricated and measured. Good agreements are achieved among the theoretic, numerical and experimental results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:191–195, 2014.     

A compact planar inverted‐F antenna with U‐shaped strip for all‐metal‐shell handset application

A compact dual‐band planar inverted‐F antenna (PIFA) with U‐shaped strip is proposed in this work for all‐metal‐shell mobile telephone application. As metal‐shell handsets are getting more and more popular nowadays, it raises a big challenge in antenna design as the metal‐shell associated with surrounding electronic components like front‐back‐cameras and telephone receiver would affect the antenna performance. This work provides an optional solution to alleviate this problem, where the metal shell of the handset and a U‐shaped strip are utilized as part of the antenna. The proposed antenna is able to generate radiation at 2.4 GHz for Wi‐Fi application with the help of the metal shell while using the U‐shaped strip can achieve a resonance at 1.575 GHz for GPS application. A prototype has been fabricated to verify the radiation performance in a practical handset test environment.     

Toward high‐resolution,inkjet‐printed,quantum dot light‐emitting diodes for next‐generation displays

We have investigated the possibility of fabricating quantum dot light‐emitting diodes (QLEDs) using inkjet printing technology, which is the most attractive method for the full‐color patterning of QLED displays. By controlling the quantum dot (QD) ink formulation and inkjet printing condition, we successfully patterned QLED pixels in the 60‐in ultrahigh definition TV format, which has a resolution of 73 pixels per inch. The inkjet‐printed QLEDs exhibited a maximum luminance of 2500 cd/m². Although the performance of inkjet‐printed QLEDs is low compared with that of QLEDs fabricated using the spin‐coating process, our results clearly indicate that the inkjet printing technology is suitable for patterning QD emissive layers to realize high‐resolution, full‐color QLED displays.     

Color tuning of indium phosphide quantum dots for cadmium‐free quantum dot light‐emitting devices with high efficiency and color saturation

Semiconductor quantum dots (QDs) promise facile color tuning and high color saturation in quantum‐dot light‐emitting devices (QD‐LEDs) by controlling nanoparticle size and size distribution. Here, we demonstrate how this promise can be practically realized for the cadmium‐free InP/ZnSe/ZnS multishell quantum dots. We developed a set of synthesis conditions and core/shell compositions that result in QDs with green, yellow, and red emission color. The QD‐LEDs employing these QDs show efficient electroluminescence (EL) with luminance up to 1800 cd/m² and efficiency up to 5.1 cd/ A . The color coordinates calculated from the EL spectra clearly demonstrate the outstanding color saturation as an outcome of the narrow particle size distribution. These results prove that the performance gap between cadmium‐free and cadmium‐based QDs in QD‐LEDs is shrinking rapidly.     

Silicon‐nanocrystal‐based photosensor integrated on low‐temperature polysilicon panels

Abstract— A photodetector using a silicon‐nanocrystal layer sandwiched between two electrodes is proposed and demonstrated on a glass substrate fabricated by low‐temperature poly‐silicon (LTPS) technology. Through post excimer‐laser annealing (ELA) of silicon‐rich oxide films, silicon nanocrystals formed between the bottom metal and top indium thin oxide (ITO) layers exhibit good uniformity, reliable optical response, and tunable absorption spectrum. Due to the quantum confinement effect leading to enhanced phonon‐assisted excitation, these silicon nanocrystals, less than 10 nm in diameter, promote electron‐hole‐pair generation in the photo‐sensing region as a result resembling a direct‐gap transition. The desired optical absorption spectrum can be obtained by determining the thickness and silicon concentration of the deposited silicon‐rich oxide films as well as the power of post laser annealing. In addition to obtaining a photosensitivity comparable to that of the p‐i‐n photodiode currently used in LTPS technology, the silicon‐nanocrystal‐based photosensor provides an effective backlight shielding by the bottom electrode made of molybdenum (Mo). Having a higher temperature tolerance for both the dark current and optical responsibility and maximizing the photosensing area in a pixel circuit by adopting a stack structure, this novel photosensor can be a promising candidate for realizing an optical touch function on a LTPS panel.     

Active matrix QD‐LED with top emission structure by UV lithography for RGB patterning

We have developed full colour top emitting quantum dot light‐emitting diode (QD‐LED) display driven by a 176‐ppi active matrix of metal oxide thin‐film transistors. Red, green and blue (RGB) QD‐LED subpixel emission layers are patterned by our original UV photolithography process and materials. We also demonstrate the potential to achieve high resolution such as 528 ppi using this process.     

基于有限元分析和结构优化的飞机垂尾质量估算

为在总体设计阶段较准确地估算飞机的质量,以垂尾为研究对象,提出基于有限元分析和结构优化的垂尾质量估算方法.该方法的主要步骤为:用CATIA实现垂尾的参数化定义并生成CAD模型;用AVL软件进行气动载荷分析;用PCL编写程序将CAD模型导入MSC Patran中,并应用其结构优化功能计算得到垂尾质量.在iSight中实现...     

Dual‐wideband filtering power divider based on center‐fed three‐line coupled structure

In this article, a dual‐wideband filtering power divider is proposed by using a center‐fed three‐line coupled structure with three open stubs and two isolation resistors. The center‐fed three‐line coupled structure can generate two wide passbands separated by a transmission zero (TZ). The three open stubs can achieve four TZs around the two passbands, which is conducive to the frequency selectivity. Compared with the reported designs, the bandwidth is extended and the performance of isolation, insertion loss and circuit size can reach balance. The proposed design is implemented with size of 0.22 λ_g × 0.39 λ_g (λ_g is the guided wavelength at the center frequency of the lower passband) which exhibits the 3‐dB fractional bandwidths of 56.5%/24.27% and the insertion loss of 0.51/0.68 dB at the center frequency of two passband (f₁/ f₂) of 1.94/4.2 GHz, while the isolation at f₁/f₂ are higher than 22.5/20.1 dB.     

Miniaturization of frequency‐selective rasorber based on 2.5‐D knitted structure

Knitted structure based on through‐silicon vias is utilized to realize the miniaturization of frequency‐selective rasorber (FSR). According to equivalent circuit model analysis, additional inductance and capacitance introduced by an array of metal vias are considered, which is combined with lossy cross‐frame and lossless double square‐loop structure to realize the function of FSR. Through full wave simulation, the proposed 2.5‐D FSR demonstrates one passband between two absorption bands. The simulated results indicate a significant size reduction with P = 0.15 λ_L, where λ_L is the free‐space wavelength at the lowest frequency of ‐10 dB reflection. Moreover, an insertion loss of 0.49 dB can be observed at 3.99 GHz, the fractional bandwidth for reflection coefficients less than ‐10 dB is 100%, and the thickness of the whole structure is 0.138 λ_L, respectively. In addition, the frequency response of this miniaturized FSR is stable for incident angle up to 40° and both linear polarizations. After then, the prototype of this 2.5‐D FSR is fabricated and measured, which shows reasonable agreement with simulated results.     

基于拓扑序列和量子遗传算法的贝叶斯网结构学习

贝叶斯网是处理不确定性问题知识表示和推理的最重要的理论模型之一,其结构学习是目前研究的一个热点。提出了一种基于拓扑序列和量子遗传算法的贝叶斯网结构学习算法,新算法首先利用量子信息的丰富性和量子计算的并行性,设计出基于量子染色体的拓扑序列生成策略提高了搜索效率,并为K2算法学得高质量的贝叶斯网结构提供了保障;然后采用带上下界的自适应量子变异策略,增强了种群的多样性,提高了算法的搜索能力。实验结果表明,与已有的一些算法相比,新算法不仅能获得较高质量的解,而且还有着较快的收敛速度。     

A BTB UWB power divider with arbitrary power‐dividing ratio based on three‐slotline structure

In this article, a balanced‐to‐balanced (BTB) ultra‐wide band (UWB) power divider (PD) is proposed, which can realize arbitrary power‐dividing ratio (PDR) with improved transmission bandwidth flatness. The proposed PD is primarily based on microstrip/slotline (MS) transition structures and parallel‐coupled three‐slotline structure. U‐type microstrip feed lines integrated with stepped‐impedance slotline resonators are adopted at the input and output ports, which make the differential‐mode (DM) responses independent of the common‐mode (CM) ones. Meanwhile, superior DM transmission and CM suppression are achieved intrinsically, thereby simplifying the design procedure significantly. By changing the distances between the coupled three slotlines, the PDR between the output ports is controllable. In order to verify the feasibility of the proposed design method, several prototype circuits of the proposed PDs with different PDRs are simulated and a prototype circuit with the 2:1 PDR is fabricated and measured. A good agreement between the simulation and measurement results is observed.     

Electronic structure and electrical conductivity of MgO protecting layer in plasma‐display panels: A tight‐binding quantum chemical study

Abstract— The tight‐binding quantum chemical molecular dynamics code, Colors, has been successfully applied to the electronic‐structure calculations of the MgO‐protecting‐layer model in plasma‐display panels (PDPs). The code succeeded in reproducing the band‐gap energy of the MgO crystal structure. The energy gap between the bottom of the conduction band (CB) and the top of valence band (VB) was 7.45 eV, which is in quantitative agreement with the experimental and previous theoretical results. The electronic structure of the undoped MgO model and Si‐doped MgO model was also calculated. The impurity level was 2.15 eV lower than that for the bottom of the CB. This result was in qualitative agreement with recent cathodoluminescence measurements. In addition, we have already succeeded in developing a novel electrical conductivity simulator using the spatial distribution of the probability density of wave functions obtained from the tight‐binding quantum chemical molecular dynamics code, Colors. The electrical conductivity of the MgO‐protecting‐layer model was estimated with and without an oxygen defect and a significant change in the electrical conductivity of the MgO‐protecting‐layer materials was observed with the introduction of oxygen defects.     

Wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure

In this article, a wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure is presented. By means of the differential microstrip‐slot‐line‐microstrip transition, the proposed filter has a wideband bandpass filtering response. Simultaneously, the utilization of the strip‐loaded slot‐line extends its upper stop‐band. The proposed bandpass filter has wider upper‐stopband, wideband bandpass response, and intrinsic high common‐mode (CM) suppression. To verify the design concept, one filter example has been designed, fabricated, and measured. It has a differential‐mode (DM) 3‐dB fractional bandwidth of 157% with a low 0.82 dB minimum insertion loss. What's more, it shows a very wide 20 dB DM stop‐band bandwidth of 6.5 f_0d. The experienced results are in good agreement with the theoretical and simulated results.