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In the near future, technological advances driven by the Fourth Industrial Revolution will boost the demand for integrated, power-efficient miniature lasers, which are important for optical data communications and advanced sensing applications. Although top-down fabricated III-V semiconductor micro-disk and micro-ring lasers have been shown to be efficient light sources, challenges such as etching-induced sidewall roughness and poor fabrication scalability have been limiting the potential for high-density on-chip integration. Here, we demonstrate InP micro-ring lasers fabricated with a highly scalable epitaxial growth technique. With an optimized cavity design, the optically pumped micro-ring lasers show efficient room-temperature lasing with a lasing threshold of around 50 μJ cm-2 per pulse. Remarkably, through comprehensive modeling of the micro-ring laser, we demonstrate lasing mode engineering experimentally by tuning the vertical ring height. Our work is a major step toward realizing the high-density monolithic integration of III-V miniature lasers on submicrometer-scale optoelectronic devices.

Random lasers are promising, easy-to-fabricate light sources that rely on scattering instead of well-defined optical cavities. We demonstrate random lasing in GaAs nanowires using both randomly oriented and vertically aligned arrays. These configurations are shown to lase in both resonant and nonresonant modes, where aligned nanowires support predominantly resonant lasing and randomly oriented favors nonresonant lasing. On the basis of numerical simulations, aligning the nanowires increases the system's scattering efficiency leading to higher quality factor modes and thus favoring the resonant modes. We further demonstrate two methods to optically suppress resonant mode lasing by increasing the number of excited modes. The light output-light input curves show a pronounced kink for the resonant lasing mode while the nonresonant mode is kink-free. The resonant lasing modes may be used as tunable lasers, and the nonresonant modes exhibit near-thresholdless amplification. Switching between lasing modes opens up new opportunities to use lasers in broader applications.

The purpose of this study was to find the coding RNA [messenger RNA (mRNA)] and long noncoding RNA (lncRNA) expressed in keloid through the analysis of Gene Expression Omnibus microarray chip of keloid fibroblasts.Gene Expression Omnibus database GSE7890 database was downloaded with selection of keloids and normal scar group data. The data were analyzed by R language combined with online database. The log2FC1, P value0.01 was chosen as screening criteria, and the differentially expressed mRNAs were screened for GO and KEGG function analysis.One hundred fifty-five mRNA expression in the keloid group was significantly different from that in the normal group, including 31 groups with upregulated mRNA expression and 124 groups with down-regulated mRNA expression. Meanwhile, 8 lncRNAs were changed in the keloid group, including 3 upregulated (Rp11-420a23.1, Rp11-522b15.3, and Rp11-706j10.1) and 5 down-regulated (LINC00511, LINC00327, Hoxb-as3, Rp11-385n17.1, and Rp3-428l16.2). Quantitative polymerase chain reaction analysis of DElncRNAs in keloid fibroblasts showed that the expression of all DElncRNAs except for RP11-385N17.1 was increased in the keloid group compared with the control group. Moreover, the differences in LINC00511 and RP11-706J10.1 were statistically significant.The noncoding RNA information of Gene Expression Omnibus chip data can be deeply mined through bioinformatics, and the potential epigenomic mechanism affecting keloid formation can be found from the existing database.

In the past decade, the structural and electronic properties of monolayer-protected metal clusters, which can be produced size-selected in macroscopic amounts, have received a lot of attention. Their great potential for optical applications has been identified. In the high intensity regime, monolayer-protected metal clusters show pronounced nonlinear absorption and refraction. Naturally, these phenomena are wavelength-dependent, however, such dependence is largely unexplored. Here, we quantify the wavelength-dependent non-linear optical absorption and refraction cross sections of atomically precise Au

Quantifying historical extreme drought is crucial to better understand and contextualize historical extreme droughts and prepare for extreme drought events that may occur in the future. However, the potential impacts of extreme droughts such as those in historical records considering modern day drought resistance and mitigation capacities remain unclear. In order to present the methods of reconstructing historical drought recurrence and conduct a historical drought recurrence scenario analysis under the current defense conditions, a modern day recurrence of the Guangxu drought during the Qing Dynasty from 1875 to 1879 was proposed using the Qing Palace Archives. In which, the historical annual precipitation in core drought areas was quantitatively reconstructed based on snow-rain records derived from the Qing Dynasty archives. And the extreme Guangxu drought was analyzed by establishing the corresponding relationship between precipitation anomaly percentage and the historical drought catalog. This allowed for the characterization of possible impacts of severe drought on water resources, water supply, food production, and economy under current defense conditions. The results showed that if the Guangxu drought occurred today under the current natural geographical conditions, core drought areas like Beijing, Tianjin, Hebei, Shanxi, Shaanxi, Henan, and Shandong would experience water shortages greater than 50% of their multi-year average water resources. In addition, we found that water transfer projects and large-medium-sized reservoirs will play central roles in drought mitigation in the event of an historical extreme drought.

Miniaturized light sources are important component for the development of on-chip optical networks. In this work, InGaAs/InP single quantum well (QW) nanowire array light emitting diodes (LEDs) with high uniformity have been demonstrated at telecommunication wavelength with high-speed modulation towards GHz-level operation.

In the near future, technological advances driven by the Fourth Industrial Revolution will boost the demand for integrated, power-efficient miniature lasers, which are important for optical data communications and advanced sensing applications. Although top-down fabricated III-V semiconductor micro-disk and micro-ring lasers have been shown to be efficient light sources, challenges such as etching-induced sidewall roughness and poor fabrication scalability have been limiting the potential for high-density on-chip integration. Here, we demonstrate InP micro-ring lasers fabricated with a highly scalable epitaxial growth technique. With an optimized cavity design, the optically pumped micro-ring lasers show efficient room-temperature lasing with a lasing threshold of around 50 μJ cm-2 per pulse. Remarkably, through comprehensive modeling of the micro-ring laser, we demonstrate lasing mode engineering experimentally by tuning the vertical ring height. Our work is a major step toward realizing the high-density monolithic integration of III-V miniature lasers on submicrometer-scale optoelectronic devices.

Random lasers lase in two types of modes: resonant and nonresonant modes. The resonant modes could be used in tunable lasers while the nonresonant modes could lase at low thresholds. Here, methods to manage modes in nanowires based random lasers are shown and discussed.

In order to further improve the output power of W-band traveling wave tube (TWT), a low gain TWT was proposed as a secondary amplifier. It uses a double staggered grating slow wave structure (DSG-S...

A novel helical groove rectangular waveguide slow wave structure (HGRW-SWS) which evolves from the double staggered grating waveguide (DSGW) SWS is put forward to develop the high-gain and high electron efficiency terahertz (THz) traveling wave tube (TWT). The major advantages of the HGRW SWS are the higher interaction impedance, lower ohmic loss, and lower phase velocity especially in higher frequency band compared with the DSGW SWS. The gain and electron efficiency of TWT using HGRW-SWS have been significantly improved, respectively, compared with the TWT using DSGW-SWS.

GaInP alloy could be the most trusted key material for fabricating super-high-efficiency single- and multi-junction solar cells, especially for space applications. The storage and transfer of optical excitation energy in this key alloy is thus a key subject of the energy conversion from optical to electrical. In this article we present a study of the subject through investigating photoluminescence (PL) degradation in the GaInP epilayer at 4 K under the continuous optical excitations of ultraviolet (UV) 325 nm, visible 488.0 and 514.5 nm lasers. It is found that the decline of PL intensity with the irradiation time may be represented by I ( t ) / I 0 = 1 + t τ − 1 − 1 + C , where I 0 is the luminescence intensity at the beginning of irradiation, τ a time constant, and C a background. Moreover, the PL degradation degree reduces with increasing the excitation wavelength. In addition, some red shift of the PL peak is observed accompanying with the intensity decline under the UV laser excitation. These PL signatures indicate that the localized carriers within the local atomic ordering domains play a major role in the storage and transfer of the excitation energy via photon recycling processes.

A generalized model for temperature-dependent time-resolved photocurrent of minority charge carriers in doped semiconductors is developed. The model is then applied to quantitatively interpret the time-resolved photocurrent data of a GaInP solar cell at different temperatures. Moreover, an analytical relationship between photocurrent and photoluminescence lifetimes is derived for the minority carriers. Under the conditions of zero external electric field, mobility and hence diffusion coefficient of minority carriers can be obtained from the measured photocurrent and photoluminescence lifetimes. This study thus may provide a deeper insight into the effective lifetimes of functional carriers in doped semiconductors and even in solar cells.

The role of exciton–phonon coupling in light emission in cesium lead bromide (CsPbBr3) nanosheets is investigated with combined photoluminescence spectroscopy and the multimode Brownian oscillator ...

Among the known color centers of diamond, the nitrogen-vacancy (NV) center composed of a substitutional nitrogen and its nearest carbon vacancy could be the most promising photon emitter. In this work, we present the micro-photoluminescence (μ-PL) landscapes of two quasi-localized vibrational resonances (∼45 and ∼63 meV) associated with the neutral (NV0) and negative (NV−) NV centers, respectively. A symmetric electron–phonon coupling theoretical model was used to simulate the μ-PL spectra with vibronic structures, so that the effective phonon densities of states and Huang–Rhys factors could be obtained for the two charge states of the NV centers. Our study also reveals that the perfect lattice optical phonon mode plays a more significant role in the luminescence of the NV0 state, whereas the quasi-localized vibrational resonance plays the dominant role in the case of NV−. These new results may deepen the existing understanding of the luminescence properties of the NV centers in diamond.

All-inorganic lead halide perovskite quantum dots (PQDs) of CsPbBr3 were synthesized at room temperature via a facile solution-based procedure. The cubic phase structure of the synthesized PQDs was judiciously identified through examining high-resolution transmission electron microscopy (TEM) images, selected area electronic diffraction (SAED) patterns and scanning TEM images of the PQDs. Variable-temperature photoluminescence (PL) spectra of the CsPbBr3 PQDs randomly embedded into a frozen solid of methylbenzene were measured in the temperature range of 5-180 K. It is found that both the linewidth and peak position of the measured PL spectra are abnormally almost temperature independent in the temperature range of interest. Some competing mechanisms, such as a competition between the bandgap blue shift induced by thermal lattice expansion and red shift induced by thermal escaping of localized excitons, and a competition between lineshape broadening by phonon scattering and narrowing by thermal escaping of localized excitons, are proposed to interpret the phenomena. Good agreement between the theoretical fitting and the experimental data leads to a state-of-the-art understanding of the temperature-dependent luminescence of the CsPbBr3 PQDs in a solid matrix.

Droughts are one of the costliest natural disasters. Reliable drought monitoring and prediction are valuable for drought relief management. This study monitors and predicts droughts in Xinjiang, an arid area in China, based on the three drought indicators, i.e., the Standardized Precipitation Index (SPI), the Standardized Soil Moisture Index (SSMI) and the Multivariate Standardized Drought Index (MSDI). Results indicate that although these three indicators could capture severe historical drought events in the study area, the spatial coverage, persistence and severity of the droughts would vary regarding different indicators. The MSDI could best describe the overall drought conditions by incorporating the characteristics of the SPI and SSMI. For the drought prediction, the predictive skill of all indicators gradually decayed with the increasing lead time. Specifically, the SPI only showed the predictive skill at a 1-month lead time, the MSDI performed best in capturing droughts at 1- to 2-month lead times and the SSMI was accurate up to a 3-month lead time owing to its high persistence. These findings might provide scientific support for the local drought management.

Drought risk assessment is a vital part of drought risk management, which plays an important role in drought mitigation. Due to its complexity, drought risk is difficult to define and challenging to quantitatively assess, as the drought impacts associate with many social sectors. This contribution method the issue by quantitatively evaluating the yield loss due to drought as a function of the drought severity indicator in Liaoning province, China for spring maize using logarithmic regression. As crop water deficit is essence to identify agricultural drought, it developed a drought severity indicator using the crop water stress coefficient and duration. The Agricultural Production Systems sIMulator (APSIM) crop model was employed to simulate the spring maize growth to obtain daily water deficit during the growth period (May to September) and yield. The relationship between drought severity frequency and yield loss rate due to drought was established to assess the drought risk of spring maize when drought severity frequency is equal to 20%, 10%, 5% and 2%. The results show that Chaoyang and Fuxin have the highest drought risk in four levels of drought severity frequency whilst the lowest drought risk was identified in Tieling. The central Liaoning province has a moderate drought risk. For a specific drought severity frequency, drought risk increases from east to west in Liaoning province whilst it varies in each city at different drought severities. This method can predict yield loss due to drought for drought early warning. Drought risk maps presents spatial characteristics that can help to agricultural drought mitigation and the development of drought preparedness plan in Liaoning province.

Drought is always triggered by long-term deficit of precipitation and extreme temperature, which had led to huge losses of the economy in China. But to what extent have we defined the drought scale in contrast to farmland, river basin, grassland, forests and other types of the underlying surface? It is a vital issue for improving the accuracy of drought monitoring model/system. This study focused on developing an integrated drought assessment model which can reveal the relatively reasonable true drought circumstances and improve the monitoring ability of professional drought monitoring operation system. The object-oriented method was merged into the drought monitoring model. In order to verify the accuracy of the integrated drought assessment model, the model was applied in the professional operated drought monitoring system of Anhui Province. The monitoring system can automatically serve the daily drought monitoring map which directly shows the spatial distribution and intruded area within 4 diverse drought levels. The monitoring results indicated Anhui Province has suffered a persistent drought since the second half of 2019. And the severe drought was released by effective precipitation during August 10-13, which was caused by Typhoon Lekima. Then the drought-prone region and drought severity were consistently increasing until the extensive precipitation process in the whole province during November 26-27. The real drought development and changing phases were accurately detected by the integrated drought assessment model. And the drought impact areas from the model were coincidence with the reported data from local government. Beside that, monitoring results were approved by the local professional personnel and experts for drought monitoring.

Existing gauging networks are sparse and not readily available in real-time over the transboundary Lancang−Mekong River (LMR) basin, making it difficult to accurately identify drought. In this study, we aimed to build an operational real-time Lancang−Mekong drought monitor (LMDM), through combining satellite real-time data and the Variable Infiltration Capacity (VIC) hydrological model at a 0.25° spatial resolution. Toward this, three VIC runs were conducted: (1) a 60-year (1951−2010) historical simulation driven by Princeton’s global meteorological forcing (PGF) for yielding ‘normal’ conditions (PGF-VIC), wherein the VIC was calibrated with 20-year observed streamflow at six hydrological stations; (2) a short-period (2011−2014) simulation to bridge the gap between the historical and the real-time modeling; (3) the real-time (2015−present) simulation driven by bias-corrected satellite data, wherein the real-time soil moisture (SM) estimate was expressed as percentile (relative to the ‘normal’) for drought monitoring. Results show that VIC can successfully reproduce the observed hydrographs, with the Nash−Sutcliffe efficiency exceeding 0.70 and the relative bias mostly within 15%. Assessment on the performance of LMDM shows that the real-time SM estimates bear good spatial similarity to the reference, with the correlation coefficient beyond 0.80 across >70% of the domain. In terms of drought monitoring, the LMDM can reasonably reproduce the two recorded droughts, implying extreme droughts covering the Lower LMR during 2004/05 and widespread severe 2009/10 drought across the upper domain. The percentage drought area implied by the LMDM and the reference is close, corresponding to 66% and 60%, 43% and 40%, and 44% and 36% for each typical drought month. Since January 2015, the LMDM was running in an operational mode, from which the 2016 unprecedented drought was successfully identified in Mekong Delta. This study highlights the LMDM’s capability for reliable real-time drought monitoring, which can serve as a valuable drought early warning prototype for other data-poor regions.

By "seeing" the green two-photon luminescence, two separate focusing points are observed on the propagation axis of a converging femtosecond laser beam in a ZnO single crystal rod. It is found that the self-focusing effect makes a significant contribution to the formation of the first focusing point, while the second focusing point is caused by self-refocusing. The position of the first focusing point is in good agreement with the value predicted by a model developed by Chin and his co-workers. These experimental findings could be the unprecedented evidence for the self-focusing and refocusing effect of the femtosecond laser filament propagation in nonlinear media.

Currently, hunting for anti-temperature-degradation high-efficiency phosphors has become crucially significant for fabricating high-brightness phosphor-converted white light-emitting diodes (pc-WLEDs). Herein, we show that photoluminescence in a kind of full-solution-processed K2SiF6:Mn4+ red phosphor exhibits an extraordinarily large negative thermal quenching property. For instance, under the excitation of 477 nm laser light, the sample photoluminescence intensity amazingly increases by 347-fold when the temperature is increased from 4 to 477 K. The temperature-driven transition probability enhancement of the phonon-induced luminescence around Mn4+ ions in the phosphor is argued to be responsible for the large negative-thermal-quenching phenomenon. We also demonstrate a pc-WLED with Ra of 82 and correlated color temperature of 2701 K by using the K2SiF6:Mn4+ red phosphor + commercial yellow phosphor of YAG:Ce3+.

We present a study of recombination dynamics and lifetimes of minority carriers in a GaInP/GaAs heterostructure single-junction solar cell by using a variable-temperature time-resolved photoluminescence (TRPL) technique. It was found that the minority carriers, i.e., electrons, in the p-type GaInP base layer have super long lifetimes of ∼220 μs under the excitation of nanosecond laser pulses. On the basis of a newly developed model for time-resolved luminescence of a localized-state ensemble [e.g., Z. C. Su and S. J. Xu, Sci. Rep. 7, 13 (2017)], it is revealed that as much as 38% of photons emitted by localized carriers may be involved in the photon recycling in the GaInP base layer. The effective photon recycling is believed to be an important factor that causes the super long lifetime of the minority carriers, and can help reduce the radiative recombination loss of photogenerated carriers in heterostructure based solar cells.

Carbon nanodots (CDs), a new star in the carbon nanomaterials family, have been demonstrated to show strong luminescence, and can meet the needs of large-scale production for biological and medical applications due to their low toxicity and biocompatibility. However, their luminescence mechanisms, such as color tuning and strong excitation-dependent luminescence, are still unclear. Herein, we present a state-of-the-art understanding and manipulating luminescence in CDs by changing their environmental states and using multiple spectroscopic methods as well as the first-principles theoretical calculations. Our study reveals that the edge-carbon atoms and incorporated nitrogen atoms play critical roles in the luminescence mechanisms of CDs, and thus paves the way for manipulation of luminescence in CDs.

Human interventions (HI) are significantly affecting the land surface hydrological cycle, and thus altering the occurrence of hydrological drought. So far, however, how HI affect the propagation from meteorological to hydrological drought is still unclear. In this study, we proposed a quantitative diagnosis framework and assessed the impacts of HI on drought propagation across varying scales over the typical reservoir-dominant Daling River basin (DRB) in China, in which the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) were utilized to identify the meteorological drought (MD) and hydrological drought (HD), respectively. Our results show that the in-situ streamflow records were found with an evident turning point around 2003, coincident with the operation of the largest reservoir in DRB. Under the influence of reservoir operation, the HD frequency saw an obvious intensification and the correlations between MD and HD exhibited a decreasing tendency, especially during the wet season. The seasonality of drought propagation changed significantly for both up-downstream and MD-HD, as indicated by the advance of drought events from autumn to summer and the aggravation of autumn drought. The reservoir operation changed the HD events characteristics by increasing the drought duration and severity. Our results highlight the strong aggravating effect of reservoirs on drought propagation.

In this article, we present an in-depth optical study on luminescence spectral features and the thermal effect of the magnetic dipole (MD) transitions (e.g., the R lines of 2E → 4A2) and the associated electric dipole transitions (e.g., phonon-induced sidebands of the R lines) of Cr3+ ions in ytterbium–yttrium aluminum garnet polycrystalline transparent ceramic. The doubly split R lines predominately due to the doublet splitting of the 2E level of the Cr3+ ion in an octahedral crystal field are found to show a very large anisotropy in both emission intensity and thermal broadening. The large departure from the intensity equality between them could be interpreted in terms of large difference in coupling strength with phonons for the doubly split states of the 2E level. For the large anisotropy in thermal broadening, very different effective Debye temperatures for the two split states may be responsible for it. Besides the 2E excited state, the higher excited states, for example, 4T1 and 4T2 of the Cr3+ ion...