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Two novel bipolar deep‐blue fluorescent emitters, IP‐PPI and IP‐DPPI, featuring different lengths of the phenyl bridge, were designed and synthesized, in which imidazo[1,2‐a]pyridine (IP) and phenanthroimidazole (PI) were proposed as an electron acceptor and an electron donor, respectively. Both of them exhibit outstanding thermal stability and high emission quantum yields. All the devices based on these two materials showed negligible efficiency roll‐off with increasing current density. Impressively, non‐doped organic light‐emitting diodes (OLEDs) based on IP‐PPI and IP‐DPPI exhibited external quantum efficiencies (EQEs) of 4.85 % and 4.74 % with CIE coordinates of (0.153, 0.097) and (0.154, 0.114) at 10000 cd m−2, respectively. In addition, the 40 wt % IP‐PPI doped device maintained a high EQE of 5.23 % with CIE coordinates of (0.154, 0.077) at 10000 cd m−2. The doped device based on 20 wt % IP‐DPPI exhibited a higher deep‐blue electroluminescence (EL) performance with a maximum EQE of up to 6.13 % at CIE of (0.153, 0.078) and maintained an EQE of 5.07 % at 10000 cd m−2. To the best of our knowledge, these performances are among the state‐of‐the art devices with CIEy≤0.08 at a high brightness of 10000 cd m−2. Furthermore, by doping a red phosphorescent dye Ir(MDQ)2 (MDQ=2‐methyldibenzo[f,h]quinoxaline) into the IP‐PPI and IP‐DPPI hosts, high‐performance red phosphorescent OLEDs with EQEs of 20.8 % and 19.1 % were achieved, respectively. This work may provide a new approach for designing highly efficient deep‐blue emitters with negligible roll‐off for OLED applications. [ABSTRACT FROM AUTHOR]

The influence of evaporation conditions of organic semiconductor material tris(8-hydroxyquinoline)aluminium (Alq3) on the performance of organic light emitting diodes (OLEDs) is reported. In the process of organic material thermal evaporation, the chamber was dark or had white light from a 100?W filament lamp. The devices prepared in the dark show higher emission intensity and efficiency compared with the ones prepared in white light under the same driving voltage. Atomic force microscopy measurements show that surface morphology and phase of Alq3thin films are quite different for the previous cases. The different evaporation conditions are found to have direct effects on the electrical and luminance performance. The Alq3thin films prepared in the dark as active emission layers of OLEDs show higher intensity and efficiency. [ABSTRACT FROM AUTHOR]

Mg-doped AlxGa1-xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor deposition (MOCVD) using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Al0.43Ga0.57N epilayer grown under indium (In) ambient is of the order of 104 O-cm, while the resistivity of Mg-doped Al 0.43Ga0.57N grown without In assistance is of the order of 106 O-cm. The ultraviolet light-emitting diodes (UV-LEDs) using the In-assisted Mg-doped Al0.43Ga0.57N as the p-type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57N layers grown under In-ambient. [ABSTRACT FROM AUTHOR]

High‐performance deep‐blue emitters with external quantum efficiencies (EQEs) exceeding 5 % are still scarce in organic light‐emitting diodes (OLEDs). In this work, by introducing a [1,2,4]triazolo[1,5‐a] pyridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescent materials, PTPTPA and PTPTPA, were obtained. Systematic photophysical analysis showed that the TP block is suitable for constructing hybridized local and charge‐transfer (HLCT) emitters. Its moderate electron‐withdrawing ability and rigid planar structure can enhance the CT component while ensuring color purity. In addition, compared with PTPTPA, the additional phenyl ring of PTPBPTA not only increased the oscillator strength, but also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high‐lying triplet states to the singlet excited state. A nondoped device based on PTPTPA as emitter showed impressive performance with EQEmax of 7.11 % and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA, a white OLED with a high EQE of 23.85 % was achieved. The successful design of PTPTPA not only provided an optimization choice for OLED emitters, but also demonstrated the empirical rules for the design of multifunctional deep‐blue emitters. [ABSTRACT FROM AUTHOR]

Copper(I) complexes are attractive photo-functional materials due to their rich photochemical and photophysical properties. It has been proved that these new materials have potential application in many fields, such as organic light-emitting diodes, optical sensor, nonlinear optics and dye sensitized solar cells. The goal of this review is to outline the progress in this field. Many aspects, including new ligands, stereochemical control arid the construction of supramolecules design of the excited states, the high-energy emission and low-energy emission, the Cu-Cu bonding interactions and applications, are discussed. [ABSTRACT FROM AUTHOR]

We present a systematic analysis of the exciton-recombination zone within all-quantum-dot (QD) multilayer films using sensing QD layers in QD-based light-emitting diodes (QLEDs), and demonstrate the all-QD multilayer films with different sequences of layers prepared by inserting a sensing blue QD layer denoted as B at various positions within four red QD multilayers denoted as R. We also use different hole transporting layers (PVK, CBP as well as poly-TPD) to prevent the formation of leakage current and to improve the luminance. The results show that the total EL emission is mostly at the fourth (60%) and fifth (40%) QD monolayers, adjacent to ITO. This presents both decreasing current density and increasing brightness with different hole transporting layers, thus resulting in more efficient performance. [ABSTRACT FROM AUTHOR]

An optical analytical instrument based on light emitting diode (LED) incoherent broadband cavity enhanced absorption spectroscopy (LED-IBBCEAS) was developed for simultaneous measurements of HONO and NO2 in ambient air. Detection limits (for signal-to-noise ratio, SNR = 2) of 0.6 ppbv for HONO and 2 ppbv for NO2 were achieved with an optimum acquisition time of 120 s. Field intercomparison campaign at a suburban site of Tung Chung in Hong Kong was carried out. Daytime and nighttime concentrations of HONO and NO2 were recorded and compared with data from a long path absorption photometer (LOPAP) and a NOx analyzer equipped with a blue light converter. The test of such a LED-IBBCEAS setup by the measurement intercomparison with the well established HONO and NO2 measurement instruments, for the first time, in a real atmospheric environment, demonstrated the feasibility of the proposed technique for the measurement of environmental HONO and NO2 concentrations in a manner that is free of chemical and spectral interference. During the measurement period from 12:32 on May 12th to 12:32 on May 14th, 2012, the quantitative assessments from these techniques showed well agreed data. High temporal correlations of HONO with NOx and CO were observed, and possible formation sources of HONO are discussed. Occasional inconsistencies in the quantitative assessment of HONO were observed during the in-field campaign. The problems encountered by the IBBCEAS technique applied to field observation and the further improvements are discussed. [ABSTRACT FROM AUTHOR]

Fluorescence, HLCT emitters, intersystem crossing, light-emitting diodes, nitrogen heterocycles Keywords: fluorescence; HLCT emitters; intersystem crossing; light-emitting diodes; nitrogen heterocycles EN fluorescence HLCT emitters intersystem crossing light-emitting diodes nitrogen heterocycles 7187 7187 1 05/05/21 20210503 NES 210503 B The material PTPBTPA b is reported in this work, which is shown in blue in the cover picture. Combining the blue fluorescence and yellow or red phosphorescence produced high-performance WOLED, which emits white light as the color of the external circle. [Extracted from the article]

In this study, an InGaN lighting-emitting diode (LED) containing GaN/AlGaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and radiative recombination rate indicate that the proposed LED has a higher output power and an internal quantum efficiency, and a lower efficiency droop than the LED containing conventional GaN or AlGaN barriers. These improvements mainly arise from the modified energy bands, which is evidenced by analyzing the LED energy band diagram and electrostatic field near the active region. The modified energy bands effectively improve carrier injection and confinement, which significantly reduces electron leakage and increases the rate of radiative recombination in the quantum wells. [ABSTRACT FROM AUTHOR]

We report on the growth and fabrication of deep ultraviolet (DUV) light emitting diodes (LEDs) on an AlN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317 nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved. [ABSTRACT FROM AUTHOR]