Influence of Doping Concentrations in White Organic Light-emitting Diodes based on Phosphorescent Iridium Complexes

AbstractPhosphorescent white organic light-emitting diodes (PhWOLEDs) based on blue (Firpic) and yellow [(t-bt)2Ir(acac)] phosphorescent emitters with various doping concentration were reported. A PhWOLED with high performance characteristics has been obtained when the doping concentration for Firpic and (t-bt) 2Ir (acac) is 8 wt% and at 6 wt%, respectively. The Commission Internationale del’Eclairage (CIE) coordinates of the optimal PhWOLED is (0.333, 0.416) at 10V. The high performance of the optimized PhWOLED is attributed to effective host-guest energy transfer and efficient exciton recombination combining with suppressed exciton-quenching process in the emitting layers

Online Partial Discharge Detection and Location System Using Wireless Sensor Network

AbstractPartial discharge (PD) is an important indicator of insulation condition in a power transformer. In this paper, an online monitoring system for detecting and locating the PDs using Wireless Sensor Network (WSN) was proposed and realized. The system could detect the PDs and locate them with good accuracy. This system had the advantages of easy deployment and low cost. The chip CC2430 was used as a control unit and also used for RF communication in the sensing node. SimpliciTI protocol was adopted for WSN to get good accuracy for time synchronization. Experiments were conducted in a simulated environment and result showed the system was able to measure the location coordinate within a certain error range. The causes of the error and methods of improvement were discussed in this paper

To Enhance Light Extraction for Organic Light-Emitting Diodes by Body Modification of Substrate

A facile approach of body modification on substrate is introduced to enhance the light extraction for organic devices. The lateral metal reflective film (LMRF) was coated on side of substrate and microlens array (MLA) was fabricated on forward surface of substrate. The two methods of improving light output are simulated and optimized to form body modification. The metal thin film was evaporated on the side of reversal trapezoid shape substrate to form LMRF layer and the MLA with semicircle shape was fabricated on the substrate using normal photolithography process. The external quantum efficiency of fabricated organic device with body modification is ~1.8 times higher than the device with normal substrate

Large-Gap Quantum Anomalous Hall Insulators in AATiXX Class

We theoretically propose that the monolayer $A$Ti$X$ family (KTiSb, KTiBi, RbTiSb, SrTiSn) are potential candidates for large-gap quantum anomalous Hall insulators with high Chern number $\mathcal{C}=2$. Both of the topology and magnetism in these materials are from $3d$-orbitals of Ti. We construct the tight-binding model with symmetry analysis to reveal the origin of topology. Remarkably, quite different from the conventional $s$-$d$ band inversion, here the topological band inversion within $3d$ orbitals is due to the crystal field and electron hopping, while spin-orbit coupling only trivially gaps out the Dirac cone at Fermi level. The general physics from the $3d$ orbitals here applies to a large class of transition metal compounds with the space group $P4/nmm$ or $P$-$42m$ and their subgroups.Comment: 6 pages, 4 figure

A Monitoring System Design in Transmission Lines based on Wireless Sensor Networks

AbstractA smart grid application in monitoring the condition of transmission line with wireless sensor networks was described in this paper. ZigBee and GPRS (General Packet Radio Service) technology were adopted in this system to ensure normal transmission of signals, even in remote areas where there is no telecommunication service, and data could be transmitted over a long distance. In addition, the system provided warnings before the damage caused by meteorological disasters to ensure the line security

Giant anisotropic band flattening in twisted Γ\Gamma valley semiconductor bilayers

We propose a theory of anisotropic band flattening in moir\'e systems at the $\Gamma$ valley. We find that in twisted anisotropic two-dimensional crystals with a rectangular unit cell of $C_{2z}$ or mirror symmetries, a larger effective mass anisotropy $\eta=m_y/m_x$ has a stronger tendency to be further enhanced compared to that of monolayer, which leads to correlated physics in one dimension effectively. We predict twisted bilayer black phosphorus (tBBP) has giant anisotropic flattened moir\'e bands ($\eta\sim10^4$) from ab initio calculations and continuum model, where the low energy physics is described by the weakly coupled array of one-dimensional wires. We further calculate the phase diagram based on sliding Luttinger liquid by including the screened Coulomb interactions in tBBP, and find a large parameter space may host the non-Fermi liquid phase. We thus establish tBBP as a promising and experimentally accessible platform for exploring correlated physics in low dimensions.Comment: 5 pages, 4 figure

Discovering two-dimensional magnetic topological insulators by machine learning

Topological materials with unconventional electronic properties have been investigated intensively for both fundamental and practical interests. Thousands of topological materials have been identified by symmetry-based analysis and ab initio calculations. However, the predicted magnetic topological insulators with genuine full band gaps are rare. Here we employ this database and supervisedly train neural networks to develop a heuristic chemical rule for electronic topology diagnosis. The learned rule is interpretable and diagnoses with a high accuracy whether a material is topological using only its chemical formula and Hubbard $U$ parameter. We next evaluate the model performance in several different regimes of materials. Finally, we integrate machine-learned rule with ab initio calculations to high-throughput screen for magnetic topological insulators in 2D material database. We discover 6 new classes (15 materials) of Chern insulators, among which 4 classes (7 materials) have full band gaps and may motivate for experimental observation. We anticipate the machine-learned rule here can be used as a guiding principle for inverse design and discovery of new topological materials.Comment: 7 pages, 4 figure

Intrinsic antiferromagnetic topological insulator and axion state in V2WS4

Intrinsic magnetic topological insulators offers an ideal platform to explore exotic topological phenomena, such as axion electrodynamics, quantum anomalous Hall (QAH) effect and Majorana edge modes. However, these emerging new physical effects have rarely been experimentally observed due to the limited choice of suitable materials. Here, we predict the van der Waals layered V$_2$WS$_4$ and its related materials show intralayer ferromagnetic and interlayer antiferromagnetic exchange interactions. We find extremely rich magnetic topological states in V$_2$WS$_4$, including an antiferromagnetic topological insulator, the axion state with the long-sought quantized topological magnetoelectric effect, three-dimensional QAH state, as well as a collection of QAH insulators and intrinsic axion insulators in odd- and even-layer films, respectively. Remarkably, the N\'eel temperature of V$_2$WS$_4$ is predicted to be much higher than that of MnBi$_2$Te$_4$. These interesting predictions, if realized experimentally, could greatly promote the topological quantum physics research and application.Comment: 7 pages, 4 figure