Search

In order to investigate the energy evolution and failure characteristics of carbonaceous shale containing single fissure under drying−wetting cycles, the intact carbonaceous shale samples and the carbonaceous shale samples with fissure angles of 30°, 45° and 60° were prepared. MTS815 rock mechanics test system was used to conduct triaxial compression tests under different drying−wetting cycles. The influence of drying−wetting cycles on the strength, failure mode and energy evolution of single fissure carbonaceous shale were studied. The results show that the elastic energy and dissipated energy at crack initiation stress, damage stress and peak stress present exponential relationships with drying-wetting cycles. The elastic energy and dissipated energy at crack initiation stress and dissipated energy at damage stress are less sensitive to drying−wetting cycle, while the sensitivities of elastic energy at damage stress, and elastic energy and dissipated energy at peak stress are relatively high. The failure mode of carbonaceous shale is dominated by drying−wetting cycle and fissure angle, in which the drying-wetting cycle is the main controlling factor, and the fissure angle is the secondary controlling factor. It is found that tensile shear failure occurs in dry rock sample with fissure angle of 30°, while the dry rock sample with fissure angle of 45°and 60° are subjected to shear failure. With the increase of the number of drying−wetting cycles, the macroscopic length of the main crack increases, the density of secondary cracks increases, and the failure mode transforms to shear-tension composite failure. With the increase of the number of drying−wetting cycles, the energy storage level at crack initiation stress Kci and the energy storage level at damage stress Kcd increase gradually. The higher the energy storage level at crack initiation and damage stress, the more likely the crack initiation and rock damage occur. Kcd can be used as a warning indicator of rock failure. A larger Kcd indicates that the rock is more vulnerable to failure.

Perovskite light‐emitting diodes (LEDs) emitting in the pure‐red range of 630–640 nm show promise in meeting the requirement of the Rec.2100 standard for high‐resolution displays. However, the high‐performing LEDs (external quantum efficiency, EQE >20%) in the pure‐red range suffer from half‐life time (luminance drop to 50% of the initial luminance) of <1.6 h, resulting from the injection/transportation barrier and surface‐defects–induced charge carrier quenching. Herein, a bi‐ligand synergy strategy is developed to address the T50 issue: the introduction of iodide‐rich ligands with different chain length increases the vacancy formation energy of halogen ions and enhances the exciton binding energy, resulting in a high photoluminescence quantum yield of over 92%. The treated CsPbBrx/I3−x films exhibit 34‐fold improved material stability related to the control at continuous aging at 100 °C. As a result, pure‐red LEDs with CIE coordinates of (0.698, 0.301) approaching the Rec.2100 standard are reported. These pure‐red LEDs exhibit a low turn‐on voltage of 1.8 V, which is the lowest among reported pure‐red perovskite LEDs, and even 0.15 V lower than the optical bandgap energy (1.95 eV); and a maximum EQE of ≈21% with fourfold enhanced T50 relative to the best previous pure‐red perovskite LEDs. [ABSTRACT FROM AUTHOR]

Bulk gallium nitride (GaN) has shown great success in light‐emitting diodes (LEDs), but the use of its counterpart GaN quantum dots (QDs) to obtain electroluminescence has not yet been reported. In this work, the first GaN‐based QLED is demonstrated using Zn‐doped GaN (GaN: Zn) QDs, which is achieved through the combination of trap passivation, energy level adjustment, and morphology engineering. Pure GaN QDs and GaN: Zn QDs are synthesized, and it is found that Zn doping shifts the GaN QD emission from 321 to 377 nm and tunes the highest occupied molecular orbital energy level from 8.6 eV (of original GaN QDs) to 6.9 eV. Multiple washing posttreatment is further developed to improve QD film morphology and size distribution. The optimized GaN: Zn QDs are employed to fabricate solution‐processed LEDs, and the first GaN‐based QLEDs are reported with a maximum quantum efficiency of 0.004%. [ABSTRACT FROM AUTHOR]

Lanthanide ions (Yb3+ or Er3+) alloying of CsPb(Cl1‐xBrx)3 quantum dots (QDs) to emit approaching 1000 nm show promise in near‐infrared light‐emitting diodes (NIR‐LEDs). High Yb3+ alloying ratio increases the electroluminance efficiency of emission at 990 nm and enables high external quantum efficiency (EQE) of NIR‐LEDs, however, the high alloying ratio also results in inferior material stability and PLQY drop because of Yb3+‐induced nanocrystal precipitation. This study finds that the heavy alloying of Yb3+ ions causes lattice distortion and coherent energy reduction of Yb3+: CsPb(Cl1‐xBrx)3 QDs, induced by two Yb3+ ions replacing three Pb2+, which leads to the collapse of the octahedral structure in ambient conditions. It posits that spontaneous monovalent ion (Na+) alloying can address the trade‐off between material stability and emission intensity. The Na+ occupies the vacancy of Pb2+ ions, relaxing the distortion in the lattice and improving the phase stability of octahedral structure, and this optimized structure in turn allows a higher Yb3+ alloying ratio. Stability measurements show that the Na+/Yb3+ co‐alloyed films show ten‐fold higher material stability and 2.0‐fold emission efficiency related to controls. It reports that as a result Na+/Yb3+ co‐alloyed NIR‐LEDs have an EQE of 6.4% at 990 nm, which is among the highest perovskite NIR‐LEDs beyond 950 nm. [ABSTRACT FROM AUTHOR]