RESUMO
Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation lighting and displays. Considering the optimization design of both the QD and device structure is expected to improve the QLED's performance significantly but has rarely been reported. Here, we use the thick-shell QDs combined with a dual-hole transport layer device structure to construct a high-efficiency QLED. The optimized thick-shell QDs with CdS/CdSe/CdS/ZnS seed/spherical quantum well/shell/shell geometry exhibit a high photoluminescence quantum yield of 96% at a shell thickness of 5.9â nm. The intermediate emissive CdSe layer with coherent strain ensures defect-free growth of the thick CdS and ZnS outer shells. Based on the orthogonal solvents assisted Poly-TPD&PVK dual-hole transport layer device architecture, the champion QLED achieved a maximum external quantum efficiency of 22.5% and a maximum luminance of 259955 cd m-2, which are 1.6 and 3.7 times that of thin-shell QDs based devices with single hole transport layer, respectively. Our study provides a feasible idea for further improving the performance of QLED devices.
RESUMO
Climate warming and thawing of permafrost in the Qinghai-Tibet Plateau have resulted in soil erosion and the decline of soil quality. Determining the decadal variation of soil quality in the Qinghai-Tibet Plateau is the basis for scientific understanding of soil resources and the key to vegetation restoration and ecological reconstruction. In this study, we used eight indicators (including soil organic matter, total nitrogen, and total phosphorus) to eva-luate soil quality of montane coniferous forest zone (Tibet's natural geographical division zone â ¡) and montane shrubby steppe zone (zone â £) by calculating soil quality index (SQI) in the southern Qinghai-Tibet Plateau in the 1980s and 2020s. Variation partitioning (VPA) was used to examine the drivers for the heterogeneity of the spatial-temporal distribution of soil quality. The results showed that soil quality in each natural zone showed a downward trend in the past 40 years, with SQI of zone â ¡ decreasing from 0.505 to 0.484 and that of zone â £ decreasing from 0.458 to 0.425. The spatial distribution of soil nutrients and quality was heterogeneous, while soil nutrient conditions and quality in zone â ¡ were better than those in zone â £ in different periods. The VPA results indicated that the interaction of climate change, land degradation, and vegetation differences was the major cause of temporal variation in soil quality. Differences in climate and vegetation could better explain the spatial variation of SQI.
Assuntos
Pergelissolo , Solo , Tibet , Florestas , Fósforo/análiseRESUMO
The performance of the blue perovskite light-emitting diodes (PeLEDs) is limited by the low photoluminescence quantum yields (PLQYs) and the unstable emission centers. In this work, we incorporate sodium bromide and acesulfame potassium into a quasi-2D perovskite to control the dimension distribution and promote the PLQYs. Benefiting from the efficient energy cascade channel and passivation, the sky-blue PeLED has an external quantum efficiency of 9.7% and no shift of the electroluminescence center under operation voltages from 4 to 8 V. Moreover, the half lifetime of the devices reaches 325 s, 3.3 times that of control devices without additives. This work provides new insights into enhancing the performance of blue PeLEDs.
RESUMO
An ultracompact fiber inclinometer based on a bubble controlled by Marangoni force is proposed in this Letter. By coupling a 980-nm laser, the bubble can suspend in a quantum dots (QDs) liquid-core waveguide (LCW) due to the Marangoni effect. Under the excitation of a 405-nm laser, QDs LCW exhibit green emissions centered at 523â nm. When the tilt angle changes, the position of the bubble changes as well, which causes the variation of the 523-nm fluorescence intensity. The experimental results show that the sensitivity based on the peak intensity ratio (PIR) reaches 0.22/° with a linearity of 0.979 from 0° to 35°. Furthermore, the sensor has excellent stability and repeatability.
RESUMO
The emission linewidth of quantum dots (QDs) is one of the important optical properties, which is essential for the applications of QD lasers, high-quality displays, and biological imaging. However, we know less about controlling emission linewidth and its underlying mechanisms. Here we introduce a wurtzite ZnSe shell onto a wurtzite CdSe core to produce asymmetric strain due to their large, anisotropic lattice mismatch. Such asymmetric pressure induces significant splitting (ΔAB) between heavy-hole (hh) and light-hole (lh) in valence band (VB). We show that the emission intensity from the lh state (Elh) is significantly suppressed with the increasing ΔAB caused by the strong asymmetric strain. We demonstrate that the exciton-phonon coupling (EPC) is greatly inhibited under the anisotropic lattice strain. The alloying process between the core and shell occurs under the strong lattice strain and raises the longitudinal-optical (LO) phonon energy (ELO). Higher LO phonon energy declines LO phonon occupation numbers (NLO) and synergistically reduces the EPC. The asymmetrically strained alloy QDs ensemble exhibits highly bright emission with ultra-narrow linewidths of 13.8 nm (â¼520 nm) and 15.8 nm (â¼620 nm). This concept of band structure regulation via asymmetric strain can provide a new platform for high-quality QDs beyond the currently achieved.
Assuntos
Pontos Quânticos , Ligas , Pontos Quânticos/químicaRESUMO
The development of blue quantum dot light-emitting diodes (QLEDs) lags far behind that of the red and green ones, which hinders the practical commercialization of QLEDs. Balancing the charge transfer still remains a challenging task, because blue QD emitters have a deeper valence band (VB) that creates a great injection barrier impeding the hole transfer. Herein, we demonstrate that the charge transfer balance can be improved by using a tert-butyldimethylsilyl chloride-modified poly(p-phenylene benzobisoxazole) (TBS-PBO) blocking layer. The TBS-PBO acts well in blocking excess electron injection and preserving the emission efficiency of the QD emitter. Compared to the insulating blocking layers, TBS-PBO has good conductivity, thus keeping the current density at a high level. Our device delivers a notable luminance of 4635 cd m-2 at an external quantum efficiency (EQE) maximum of 17.4%. To the best of our knowledge, the luminance with EQE > 17% is the highest one to be reported for blue QLEDs.
RESUMO
We present here the successful fabrication of core-shell constructed CdZnSe@ZnSe colloidal alloy quantum dots with tunable optical properties using a hot-injection method, demonstrating great potential in photovoltaic devices. Upon employment as charge extraction materials in all-inorganic perovskite solar cells, an enhanced power conversion efficiency up to 8.65% has been achieved arising from the boosted charge transfer dynamics.