Single-Photon-Camera-Based Time and Spatially Resolved Electroluminescence Spectroscopy for Micro-LED Analysis

To investigate the operational mechanisms of micrometer-sized light-emitting diodes (micro-LEDs), we here demonstrate a transient methodology of time and spatially resolved electroluminescence spectroscopy (TSR-EL) to measure the spatial distribution of light emission from LED devices. By combining a single-photon camera (SPC) with the time-gated sampling method, we derived the time and spatially resolved electroluminescence intensity with increasing time. Benefiting from the high sensitivity of the SPC, this methodology can detect ultralow electroluminescence (EL) at the delay stage from the device operated around the turn-on voltage. Furthermore, we investigated the spatial light distribution of a typical quantum dots light-emitting diode (QLED) under different applied voltages and varied temperatures. It was found that the EL emission of the QLED device became more uniform with increasing temperature and applied voltage. Moreover, the methodology of TSR-EL is versatile to investigate other LEDs such as organic light-emitting diodes (OLEDs), micro-LEDs, etc

Three-Dimensional Dual-Site Catalysts for Industrial Ammonia Synthesis at Dramatically Decreased Temperatures and Pressures

Industrial ammonia (NH3) production via the Haber–Bosch (H–B) process is a great achievement of the 20th century, but its energy-intensive character renders NH3 production costly. Despite considerable efforts, progress in developing an efficient H–B catalyst that operates under near-ambient conditions has been slow. In this study, we leverage the confinement concept to facilitate low-temperature and low-pressure NH3 synthesis by constructing three-dimensional (3D) dual-site environments. Through first-principles calculations and microkinetic modeling, we demonstrate that the 3D confined dual site on diporphyrins can surpass the limitations imposed by energy-scaling relations, resulting in a significantly increased turnover frequency (TOF) for NH3 production. Notably, the calculated TOF is 2–3 orders of magnitude higher than that of the commercial ruthenium catalyst at the same working conditions, thus enabling a much-milder H–B process, e.g., at a dramatically decreased working pressure of 10 bar at 590 K. We believe that the strategy will pave the way for the development of economically viable alternatives to current industrial processes

Influence of Shell Thickness on the Performance of NiO-Based All-Inorganic Quantum Dot Light-Emitting Diodes

The effect of shell thickness on the performance of all-inorganic quantum dot light-emitting diodes (QLEDs) is explored by employing a series of green quantum dots (QDs) (Zn_<i>x</i>Cd_1–<i>x</i>Se/ZnS core/shell QDs with different ZnS shell thicknesses) as the emitters. ZnO nanoparticles and sol–gel NiO are employed as the electron and hole transport materials, respectively. Time-resolved and steady-state photoluminescence results indicate that positive charging processes might occur for the QDs deposited on NiO, which results in emission quenching of QDs and poor device performance. The thick shell outside the core in QDs not only largely suppresses the QD emission quenching but also effectively preserves the excitons in QDs from dissociation of electron–hole pairs when they are subjected to an electric field. The peak efficiency of 4.2 cd/A and maximum luminance of 4205 cd/m² are achieved for the device based on QDs with the thickest shells (∼4.2 nm). We anticipate that these results will spur progress toward the design and realization of efficient all-inorganic QLEDs as a platform for the QD-based full-colored displays