Efficient Quasi-2D Perovskite Based Blue Light-Emitting Diodes with Carbon Dots Modified Hole Transport Layer.

Quasi-2D perovskites based blue light-emitting diodes (LEDs) suffer from its poor electroluminescence performance, mainly caused by the nonradiative recombination in in defect-rich low-n phases and the unbalanced hole-electron injection in the device. Here, we developed a highly efficient quasi-2D perovskite based sky-blue LEDs behaving recorded external quantum efficiency (EQE) of 21.07% by employing carbon dots (CDs) as additives in the hole transport layer (HTL). We ascribe the high EQE to the effective engineering of CDs: (1) The CDs at the interface of HTLs can suppress the formation of low-efficient n = 1 phase, resulting a high luminescence quantum yield and energy transfer efficiency of the mixed n-phase quasi-2D perovskites. (2) The CDs additives can reduce the conductivity of HTL, partially blocking the hole injection, and thus making more balanced hole-electron injection. The CDs-treated devices have excellent Spectral stability and enhanced operational stability and could be a new alternative additive in the perovskite optoelectronic devices.

Efficient fiber coupling system for simultaneous beam shaping and wavelength combining based on misaligned stepped prism multiplexing.

Due to the substantial contrast in the output beam quality between the two directions of the semiconductor laser, efficiently coupling the beam directly into the fiber is difficult. In this study, an efficient shaping method based on step multiplexing of misaligned step prisms is proposed and investigated systematically. First, multiple laser stacks eliminate dark areas to improve the beam quality through the full utilization of the transmission and reflection surfaces of the misaligned stepped prisms, which also improves the efficiency of the stepped prisms. It also simultaneously realizes laser wavelength combining based on reflective surface multiplexing without affecting the quality of the beam on the premise of improving the output power. Finally, the whole beam shaping system is completed without using cut-transform-rearranging prisms. The method couples four groups of laser stacks into a single fiber with a fiber diameter of 400 µm and a numerical aperture of 0.22. It can be seen from the computer-simulated model outputs that the final fiber output power can reach 2255.4 W and that the system as a whole has a light-to-light translation rate of 88.1%.

Metasurface cutoff perfect absorber in a solar energy wavelength band.

We report a metasurface cutoff perfect absorber (MCPA) in the solar energy wavelength band based on the double Mie resonances generated from the silicon and gallium arsenide nanoring arrays grown on the Al layer in the solar energy wavelengths. A high average absorption of 0.910 in the absorption band and almost eliminated absorption in the nonabsorption band are realized within only 120 nm thick structures. The MCPA is of a sharp cutoff between the absorption and nonabsorption band, whose extinction ratio, extinction difference, and cutoff slope are 9.4 dB, 0.8, and 0.0019n m -1, respectively. The proposed MCPA suggests an efficient way to design a solar thermal absorber, which is of great importance in renewable energy, such as for solar thermal applications.

Precipitation and vegetation transpiration variations dominate the dynamics of agricultural drought characteristics in China.

Agricultural drought posing a significant threat to agricultural production is subject to the complex influence of ocean, terrestrial and meteorological multi-factors. Nevertheless, which factor dominating the dynamics of agricultural drought characteristics and their dynamic impact remain equivocal. To address this knowledge gap, we used ERA5 soil moisture to calculate the standardized soil moisture index (SSI) to characterize agricultural drought. The extreme gradient boosting model was then adopted to fully examine the influence of ocean, terrestrial and meteorological multi-factors on agricultural drought characteristics and their dynamics in China. Meanwhile, the Shapley additive explanation values were introduced to quantify the contribution of multiple drivers to drought characteristics. Our analysis reveals that the drought frequency, severity and duration in China ranged from 5-70, 2.15-35.02 and 1.76-31.20, respectively. Drought duration is increasing and drought intensity is intensifying in southeast, north and northwest China. In addition, potential evapotranspiration is the most significant driver of drought characteristics at the basin scale. Regarding the dynamic evolution of drought characteristics, the percentages of raster points for drought duration and severity with evapotranspiration as the dominant factor are 30.7 % and 32.7 %, and the percentages with precipitation are 35.3 % and 35.0 %, respectively. Precipitation in northern regions has a positive effect on decreasing drought characteristics, while in southern regions, evapotranspiration dominates the dynamics in drought characteristics due to increasing vegetation transpiration. Moreover, the drought severity is exacerbated by the Atlantic Multidecadal Oscillation in the Yangtze and Pearl River basins, while the contribution of the North Atlantic Oscillation to the drought duration evolution is increasing in the Yangtze River basin. Generally, this study sheds new insights into agricultural drought evolution and driving mechanism, which are beneficial for agricultural drought early warning and mitigation.

Centralized Excited States and Fast Radiation Transitions Reduce Laser Threshold in Carbon Dots.

As a new type of solution-processed nano-laser material, carbon dots (CDs) have shown considerable potential in optical communication, laser displays, micro/nano processing, and biomedicine. Reducing the laser threshold of the gain material is of considerable significance for further development of CDs' applications in the field of micro/nano lasers. A series of blue-emissive CDs (B-CDs) are synthesized by changing the molar ratios of the precursors (citric acid (CA): L-Cysteine (L-Cys)). B-CDs have a structure of carbon nanoparticles with their surface being modified with 5-oxo-3,5-dihydro-2Hthiazolo [3,2-a]pyridine-7-carboxylic acid (TPCA). The laser can only be generated when the molar ratio of the precursors is between 1:1 and 2:1. With an increase in this ratio, the laser threshold decreases from 341.6 to 165.5 mJ cm-2 . The decrease in the laser threshold is attributed to the increase in the radiation transition rate and centralized sp3 -related excited state levels, which are favorable for light amplification and population inversion. These results will be instructional for the reasonably design of CDs-based laser materials and prompt their potential use in practical photonics.

Simultaneously improving the quality factor and outcoupling efficiency of organic light-emitting field-effect transistors with planar microcavity.

Organic light-emitting field-effect transistors (OLEFETs) are regarded as an ideal device platform to achieve electrically pumped organic semiconductor lasers (OSLs). However, the incorporation of a high-quality resonator into OLEFETs is still challenging since the process usually induces irreparable deterioration to the electric-related emission performance of the device. We here propose a dual distributed Bragg reflector (DBR)-based planar microcavity, which is verified to be highly compatible with the OLEFETs. The dual DBR planar microcavity shows the great advantage of simultaneously promoting the quality (Q) factor and outcoupling efficiency of the device due to the reduced optical loss. As a result, a moderately high Q factor of ∼160, corresponding to EL spectrum linewidth as narrow as 3.2 nm, concomitantly with high outcoupling efficiency (∼7.1%) has been successfully obtained. Our results manifest that the dual DBR-based planar microcavity is a promising type of resonator, which might find potential applications in improving the spectra and efficiency performance of OLEFETs as well as in OLEFET-based electrically pumped OSLs.

A broadband and polarization-independent metasurface perfect absorber for hot-electron photoconversion.

We report an ultra-broadband metasurface perfect absorber from the UV to NIR region based on TiN nanostructures. A polarization-independent experimental average absorption of 0.900 (0.921 in simulation) at the wavelength band from 300 nm to 1500 nm is realized with only an 82 nm-thick TiN layer with TiO2 and MgF2 on top, which is efficiently fabricated by utilizing double-beam UV interference lithography followed by sputter coating deposition. A TiN-TiO2 hot-electron photoelectric conversion system is also simulated. An IPCE of 4% is realized at the wavelength of 710 nm and the average IPCE is 2.86% in the wavelength range of 400 nm to 1500 nm. The demonstrated device suggests an efficient way of designing and fabricating broadband perfect absorbers, which has great application potential in efficient hot-electron optoelectronic and photocatalytic systems.

Compact beam shaping design based on polarization plane multiplexing of semiconductor lasers.

Fiber coupling is difficult due to the uneven beam parameter product between the vertical and horizontal axes of semiconductor lasers. A beam shaping technique based on the combination of the internal total reflection and polarization surface of a stepped prism is proposed to achieve filling the dark area of the beam and polarization merging, as well as enabling the polarization plane to be multiplexed and the utilization rate of the polarization plane to be increased. The proposed technology can couple three groups of stacked array semiconductor lasers into a single fiber, in which the center diameter is 200 µm, and the numerical aperture is 0.22. The simulation results indicated that the output power of 1099 W and optical-optical conversion productivity of 85.8% were achieved.

Advantages of InGaN-GaN-InGaN Delta Barriers for InGaN-Based Laser Diodes.

An InGaN laser diode with InGaN-GaN-InGaN delta barriers was designed and investigated numerically. The laser power-current-voltage performance curves, carrier concentrations, current distributions, energy band structures, and non-radiative and stimulated recombination rates in the quantum wells were characterized. The simulations indicate that an InGaN laser diode with InGaN-GaN-InGaN delta barriers has a lower turn-on current, a higher laser power, and a higher slope efficiency than those with InGaN or conventional GaN barriers. These improvements originate from modified energy bands of the laser diodes with InGaN-GaN-InGaN delta barriers, which can suppress electron leakage out of, and enhance hole injection into, the active region.

A study of the reliability and validity of the Chinese version of the Nociception Coma Scale-Revised.

OBJECTIVE: The aim of the study was to check on the reliability and validity of the translated version of Nociception Coma Scale-Revised. DESIGN: Prospective psychometric study. SETTING: Rehabilitation and neurology unit in hospital. SUBJECTS: Patients with prolonged disorders of consciousness. INTERVENTIONS: None. MAIN MEASURES: The original English version of the Nociception Coma Scale-Revised was translated into Chinese. The reliability and validity were undertaken by trained raters. Intraclass correlation coefficients were used to assess inter-rater reliability and test-retest reliability. Cronbach's alpha test was used to investigate internal consistency. Spearman's correlation was used to calculate concurrent validity. The Coma Recovery Scale-revised was used to assess the consciousness of patients. RESULTS: Eighty-four patients were enrolled in the study. Inter-rater reliability of the Chinese version of Nociception Coma Scale-Revised was high for total scores and motor and verbal subscores and good for facial subscores. Test-retest reliability was high for total score and for all subscores. Analysis revealed a moderate internal consistency for subscores. For the concurrent validity, a strong correlation was found between the Nociception Coma Scale-Revised and the Face, Legs, Activity, Cry, and Consolability behavioral scale for all patients. A moderate correlation was found between the Nociception Coma Scale-Revised and the Coma Recovery Scale-revised scores for all patients. CONCLUSION: The Chinese version of Nociception Coma Scale-Revised has good reliability and validity data for assessing responses to pain in patients with prolonged disorders of consciousness.

Mechanism for doping induced p type C60 using thermally evaporated molybdenum trioxide (MoO3) as a dopant.

Thermally evaporated molybdenum trioxide (MoO3) doped C60 films, which could change n type features of pristine C60 to form a p type mixed C60 layer, are investigated by x-ray and ultraviolet photoelectron spectroscopy. It is found that C60 HOMO progressively shifts closer to the Fermi level after increased MoO3 doping concentration, and final onset of C60 HOMO is pinned at binding energy of 0.20 eV, indicating the formation of p type C60 films. It is proposed that in charge transfer induced p type C60 formation, due to large electron affinity of MoO3 (6.37 eV), electrons from HOMO of C60 could easily transfer to MoO3 to form cations and therefore increase hole concentration, which could gradually push C60 HOMO to the Fermi level and finally form p type C60 films. Moreover, clear different types of C60 species have been confirmed from UPS spectra in highly doped films.

Indium segregation measured in InGaN quantum well layer.

The indium segregation in InGaN well layer is confirmed by a nondestructive combined method of experiment and numerical simulation, which is beyond the traditional method. The pre-deposited indium atoms before InGaN well layer growth are first carried out to prevent indium atoms exchange between the subsurface layer and the surface layer, which results from the indium segregation. The uniform spatial distribution of indium content is achieved in each InGaN well layer, as long as indium pre-deposition is sufficient. According to the consistency of the experiment and numerical simulation, the indium content increases from 16% along the growth direction and saturates at 19% in the upper interface, which cannot be determined precisely by the traditional method.

First passage time distribution in stochastic processes with moving and static absorbing boundaries with application to biological rupture experiments.

We develop and investigate an integral equation connecting the first passage time distribution of a stochastic process in the presence of an absorbing boundary condition and the corresponding Green's function in the absence of the absorbing boundary. Analytical solutions to the integral equations are obtained for three diffusion processes in time-independent potentials which have been previously investigated by other methods. The integral equation provides an alternative way to analytically solve the three diffusion-controlled reactive processes. In order to help analyze biological rupture experiments, we further investigate the numerical solutions of the integral equation for a diffusion process in a time-dependent potential. Our numerical procedure, based on the exact integral equation, avoids the adiabatic approximation used in previous analytical theories and is useful for fitting the rupture force distribution data from single-molecule pulling experiments or molecular dynamics simulation data, especially at larger pulling speeds, larger cantilever spring constants, and smaller reaction rates. Stochastic simulation results confirm the validity of our numerical procedure. We suggest combining a previous analytical theory with our integral equation approach to analyze the kinetics of force induced rupture of biomacromolecules.

A Systematic Comparison of Pairwise and Many-Body Silica Potentials.

The role of many-body effects in modeling silica was investigated using self-consistent force matching. Both pairwise and polarizable classical force fields were developed systematically from ab initio density functional theory force calculations, allowing for a direct comparison of the role of polarization in silica. It was observed that the pairwise potential performed remarkably well at reproducing the basic silica tetrahedral structure. However, the Si-O-Si angle that links the silica tetrahedra showed small but distinct differences with the polarizable potential, a result of the inability of the pairwise potential to properly account for variations in the polarization of the oxygens. Furthermore, the transferability of the polarizable potential was investigated and suggests that additional forces may be necessary to more completely describe silica annealing.