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Organic phototransistors (OPTs) based on polymers have attracted substantial attention due to their excellent signal amplification, significant noise reduction, and solution process. Recently, the near-infrared (NIR) detection becomes urgent for OPTs with the increased demand for biomedicine, medical diagnostics, and health monitoring. To achieve this goal, a low working voltage of the OPTs is highly desirable. Therefore, the traditional dielectric gate can be replaced by an electrolyte gate to form electrolyte-gated organic phototransistors (EGOPTs), which are not only able to work at voltages below 1.0 V but also are biocompatible. PCDTPT, one of the most popular narrow band gap donor-acceptor copolymer, has been rarely studied in EGOPTs. In this work, an organic NIR-sensitive EGOPT based on PCDTPT is demonstrated with the detectivity of 7.08 × 10

The instability of organic–inorganic perovskites in humid air is a serious bottleneck that restricts their practical applications in optoelectronics, although tremendous achievements have been made in organic–inorganic perovskite devices. Materials engineering is believed to be one of the most direct strategies to address this issue. Mixed-dimensional organic–inorganic perovskite microcrystals, which exhibit relatively good charge carrier transport owing to the limited grain boundaries and low defect densities compared to perovskite thin films, integrate the good humidity stability of two-dimensional (2D) and single-phase quasi-2D perovskites and the high photoresponse of 3D perovskites in an individual crystal, rendering them as excellent candidates for the development of high-performance photodetectors. Herein, the (C6H5CH2CH2NH3, PEA)2(CH3NH3, MA)n−1PbnBr3n+1 (n = 1, 3, 5, ∞) perovskite microcrystals were synthesized using an anti-solvent vapor-assisted method, and the optoelectronic properties of these microcrystals were investigated by fabricating photodetectors in a lateral configuration. The (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4Pb5Br16 perovskites proved to be mixed-dimensional microcrystals, respectively, which consist of the single phases of 2D (PEA)2PbBr4, quasi-2D perovskite, and 3D MAPbBr3. The photodetectors based on the individual (PEA)2(MA)2Pb3Br10 and (PEA)2(MA)4Pb5Br16 perovskite microcrystals perform better than the (PEA)2PbBr4 microcrystal photodetector and exhibit higher humidity resistance than the MAPbBr3 device. The best performances are achieved in the (PEA)2(MA)4Pb5Br16 microcrystal photodetector with a high responsivity of 182.63 A W−1, detectivity of 2.51 × 1014 Jones, and gain of 5.58 × 102, which can detect an optical signal with an extremely low light power density of 2.47 nW cm−2. Our results demonstrate that developing mixed-dimensional perovskite microcrystals is a promising way to construct highly efficient and stable photodetectors.

Chiral light-matter interaction between photonic nanostructures with quantum emitters shows great potential to implement spin-photon interfaces for quantum information processing. Position-dependent spin momentum locking of the quantum emitter is important for these chiral coupled nanostructures. Here, we report the position-dependent chiral coupling between quantum dots (QDs) and cross waveguides both numerically and experimentally. Four quantum dots distributed at different positions in the cross section are selected to characterize the chiral properties of the device. Directional emission is achieved in a single waveguide as well as in both two waveguides simultaneously. In addition, the QD position can be determined with the chiral contrasts from four outputs. Therefore, the cross waveguide can function as a one-way unidirectional waveguide and a circularly polarized beam splitter by placing the QD in a rational position, which has potential applications in spin-to-path encoding for complex quantum optical networks at the single-photon level., 13 pages, 4 figures

Slow light in topological valley photonic crystal structures offers new possibilities to enhance light-matter interaction. We report a topological cavity based on slow light topological edge mode for broadband Purcell enhancement. The topological edge modes with large group indices over 100 can be realized with a bearded interface between two topologically distinct valley photonic crystals, featuring the greatly enhanced Purcell factor because of the increased local density of states. In the slow light regime, the topological cavity supports much more cavity modes with higher quality factor than that in the fast light regime, which is both demonstrated theoretically and experimentally. We demonstrate the cavity enables the broadband Purcell enhancement together with substantial Purcell factor, benefiting from dense cavity modes with high quality factor in a wide spectral range. It has great benefit to the realization of high-efficiency quantum-dot-based single-photon sources and entangled-photon sources with less restriction on spectral match. Such topological cavity could serve as a significant building block toward the development of photonic integrated circuits with embedded quantum emitters., Comment: 16 pages, 4 figures

Two-dimensional (2D) layered hybrid perovskites provide an ideal platform for studying the properties of excitons. Here, we report on a strong triplet-exciton and longitudinal-optical (LO) phonon coupling in 2D (C6H5CH2CH2NH3, PEA)2PbBr4 perovskites. The triplet excitons exhibit strong photoluminescence (PL) in thick perovskite microflakes, and the PL is not detectable for monolayer microflakes. The coupling strength of the triplet exciton-LO phonon is approximately two to three times greater than that of the singlet exciton-LO phonon with a LO phonon energy of about 21 meV. This difference might due to the different locations of singlet excitons located in the well and triplet excitons located in the barrier in the 2D layered perovskite. Revealing the strong coupling of triplet exciton-LO phonon provides a fundamental understanding of many-body interaction in hybrid perovskites, which is useful to develop and optimize the optoelectronic devices based on 2D perovskites in the future., Comment: 22 pages, 5 figures

Monolayer transition metal dichalcogenides have recently attracted great interests because the quantum dots embedded in monolayer can serve as optically active single photon emitters. Here, we provide an interpretation of the recombination mechanisms of these quantum emitters through polarization-resolved and magneto-optical spectroscopy at low temperature. Three types of defect-related quantum emitters in monolayer tungsten diselenide (WSe$_2$) are observed, with different exciton g factors of 2.02, 9.36 and unobservable Zeeman shift, respectively. The various magnetic response of the spatially localized excitons strongly indicate that the radiative recombination stems from the different transitions between defect-induced energy levels, valance and conduction bands. Furthermore, the different g factors and zero-field splittings of the three types of emitters strongly show that quantum dots embedded in monolayer have various types of confining potentials for localized excitons, resulting in electron-hole exchange interaction with a range of values in the presence of anisotropy. Our work further sheds light on the recombination mechanisms of defect-related quantum emitters and paves a way toward understanding the role of defects in single photon emitters in atomically thin semiconductors., Comment: 14 pages, 4 Figures

We report an out-of-plane magnetic field induced large photoluminescence enhancement in WS${}_2$ flakes at $4$ K, in contrast to the photoluminescence enhancement provided by in-plane field in general. Two mechanisms for the enhancement are proposed. One is a larger overlap of electron and hole caused by the magnetic field induced confinement. The other is that the energy difference between $\Lambda$ and K valleys is reduced by magnetic field, and thus enhancing the corresponding indirect-transition trions. Meanwhile, the Land\'e g factor of the trion is measured as $-0.8$, whose absolute value is much smaller than normal exciton, which is around $|-4|$. A model for the trion g factor is presented, confirming that the smaller absolute value of Land\'e g factor is a behavior of this $\Lambda$-K trion. By extending the valley space, we believe this work provides a further understanding of the valleytronics in monolayer transition metal dichalcogenides., Comment: 15 pages, 4 figures

Blood is not only the traces of the murder scene but also the evidence, has a very important role in the acquisition of criminal evidence and forensic identification. However, the conventional testing methodology being currently deployed in bloodstain identification may destruct the human DNA. Some investigators used the method is undeserved, often regret in the exploration of the scene. From this point of view, efficient non-destructive technology for quickly identifying bloodstain is an emerging issue in this field. In this article, a method is proposed for nondestructive testing of identifying blood stains, and design a blood model named blood band inequality model to extract blood from eight kinds of suspected blood. The validity of the model was verified by the theory and experiment. Extraction efficiency of blood is as high as 94.71%, and the omission rate is only 5.29%. Experiments proved hyperspectral imaging can be used for the non-contact detection, identification of blood stains and the new model is effective in the extraction of blood.

Quasi-two-dimensional Ruddlesden–Popper perovskites driving carrier self-separation have rapidly advanced the development of high-performance optoelectronic devices. However, insightful understanding of carrier dynamics in the perovskites is still inadequate. The distribution of multiple perovskite phases, crucial for carrier separation, is controversial. Here we report a systematic study on carrier dynamics of spin-coated (C6H5CH2CH2NH3)2(CH3NH3)n−1PbnI3n+1 (n = 3 and 5) perovskite thin films. Efficient electrons transfer from small-n to large-n perovskite phases, and holes transfer reversely with time scales from ∼0.3 to 30.0 ps. The multiple perovskite phases are arranged perpendicularly to substrate from small to large n and also coexist randomly in the same horizontal planes. Further, the carrier separation dynamics is tailored by engineering the crystalline structure of the perovskite film, which leads to controllable emission properties. These results have important significance for the design of o...

The quasi-one-dimensional (quasi-1D) TaSe3 attracts considerable attention for its intriguing superconductivity and possible interplay with nontrivial topology and charge density wave (CDW) state. However, unlike the isostructural analogues, CDW has not been observed for TaSe3 despite its quasi-1D character that is supposed to promote Peierls instabilities and CDW. Here we synthesize TaSe3 mesowires (MWs) using a one-step approach. For the MW of ~300 nm thick, a distinct CDW transition occurs at 65 K in the resistivity measurement, which has not been reported before and is further evidenced by the Raman characterization and susceptibility measurement. For comparison, we have also prepared bulk single crystal TaSe3. Although no anomaly appears in the resistivity and magnetoresistance measurements, the carrier type detected by Hall effect varies from n-type to p-type below 50 K, suggesting a reconstruction of Fermi surface that could be associated with CDW. The enhancement of CDW in the MWs is attributed to the reduced dimensionality. TaSe3 is demonstrated to be a promising platform to study the correlation and competition of CDW and superconductivity in the quasi-1D systems., 21 pages, 5 figures, Applied Physics Letters

Transition metal dichalcogenide monolayers provide an emerging material system to implement quantum photonics with intrinsic two-dimensional excitons or embedded zero-dimensional localized states. Here we demonstrate the mesoscopic localized states between two- and zero- dimensions, which is a many-body system with electron-electron Coulomb interactions. A fine structure splitting is observed, which is similar to quantum dots. Meanwhile the polarization is changed by the magnetic field, due to the nature of two-dimensional monolayers. Furthermore, a large quadratic diamagnetism with a coefficient of around $100\ \mathrm{\mu eV/T^2}$ is observed, as a unique consequence of the mesoscopic scale. The many-body effect also results in the emission energy variation and linewidth narrowing in the spectrum, which corresponds well to the theoretical analysis. These unique properties indicate the great potential of mesoscopic localized states in many-body physics and quantum photonics., Comment: 14 pages, 4 figures

The identification of bloodstain is one of the most important approaches in obtaining evidence in criminalistics. A threshold method based on spectral co-efficient and interclass variance is proposed in this paper, it is a non-contact, non-destructive method for quickly identifying bloodstains. The spectra of bloodstains and other suspected substances were all extracted from their hyper-spectral image. Then calculate the correlation coefficients of these spectral and interclass variances, analyze the differences between substances. The best blood recognition threshold was determined as 0.9. After preprocessing for eliminating systematic errors, experiments with the threshold 0.9 are carried out to identify bloodstains on the calico and red T-shirt. The method can remarkably identify the bloodstain from other non-blood substances both quickly and efficiently. The blood extraction rate can reach to 93.35% and 89.19%, respectively. It is an important step toward the implementation of bloodstain non-contact and non-destructive identification in forensic casework.

We report on controllable cavity modes through controlling the backscattering by two identical scatterers. Periodic changes of the backscattering coupling between two degenerate cavity modes are observed with the angle between two scatterers and elucidated by a theoretical model using two-mode approximation and numerical simulations. The periodically appearing single-peak cavity modes indicate mode degeneracy at diabolical points. Then interactions between single quantum dots and cavity modes are investigated. Enhanced emission of a quantum dot with a six-fold intensity increase is obtained in a microdisk at a diabolical point. This method to control cavity modes allows large-scale integration, high reproducibility and fexible design of the size, location, quantity and shape for scatterers, which can be applied for integrated photonic structures with scatterer-modified light-matter interaction., 23 pages, 5 figures

Scene-based wavefront sensing currently uses the periodic-correlation algorithm based on fast Fourier transforms. However, when the object scene contains features at the field edges, the performance of the algorithm is poor due to the periodicity of fast Fourier transforms, called wraparound effect. In this paper, we propose an algorithm based on the gradient cross-correlation. Both simulation and experiment results show its dramatic effectiveness against the wraparound effect, and a considerable improvement is obtained in image resolution with closed loop adaptive optics correction.

High-purity InAs 1 −x Sb x films with x =0.06 were successfully grown on InAs (100) substrates by liquid phase epitaxy (LPE). Procedures were applied to purify InAs 1- x Sb x precursor material, which included prolonging baking time in hydrogen and adding rare-earth element gadolinium (Gd) to the growth melt. Electrical transport properties of InAs 1- x Sb x film were investigated by Hall measurements in the condition of the conductive InAs substrate being removed completely by chemical mechanical polishing (CMP) to eliminate its influence on the measurements. Hall measurement results show carrier concentration and mobility of our InAs 1- x Sb x samples are superior to the other reported values when a combinational purification procedure is applied.

A series of InAs1−xNx films have been successfully grown on (100) oriented InAs substrates by liquid phase epitaxy technique. Samples with different nitrogen contents have been analyzed by high-resolution x-ray diffraction measurement, which confirms the incorporation of N in the epilayers. N-related modes are detected in the Raman spectra of InAs1−xNx epilayers. The fundamental absorption edges of InAs1−xNx films obtained by Fourier transform infrared transmission spectroscopy exhibit a red-shift compared with that of InAs homoepilayer.

Hybrid Perovskites have shown a great potential for applications in photovoltaics and light-emitting devices with high efficiency. Interaction between defect-induced trapped excitons and phonons plays an important role in understanding the emerging phenomena for such an excellent figure-of-merit. Here we demonstrate hot polarons with narrow linewidth in $\mathrm{CH_{3}NH_{3}PbBr_{3}}$ nanowires, which originate from the interaction between trapped excitons and octahedra-twist phonons. The observation of hot polarons in photoluminescence without gain methods indicates the large interaction strength between excitons and phonons. The multiple hot polarons are further confirmed by magneto-optical spectra with a Zeeman splitting of the trapped excitons and a phonon energy increase with diamagnetic effect. Furthermore, the phonons participating in the interaction are demonstrated to be the octahedra-twist vibrations which are transverse optical phonons, while the interaction between trapped excitons and longitudinal optical phonons is weak. Our work demonstrates that trapped excitons in perovskites prefer to interact with transverse rather than longitudinal optical phonons. Since bulk materials usually interact with longitudinal optical phonons, this result provides a physical explanation of the high tolerance of defects in perovskites., Comment: 16 pages, 4 figures

The fast and on-site measurement of the real-time of seeds is of great importance for the farmers and scientists, but is difficult to achieve. At present, there are very few researches reported for this issue. Therefore, it is top urgent to develop an effective method of the determination of real-time of seeds. This study develops the spectral indices using the hyperspectral imaging technique for rapid detection of real-time of seeds. The hyperspectral reflectance images are acquired from five year of wheat seeds over the spectral region between 400 and 1000 nm. Mean and variance of the wheat seeds each year are extracted utilizing the software of the environment for visualizing images (ENVI). The two spectral indices (NDVI and EVI) are built according to the mean and variance of different years. The excellent determination results for real-time of wheat seeds are yielded employing the NDVI and EVI spectral index (with coefficient of determination R2 = 0.9398 and R2=0.6339). This work demonstrates that the hyperspectral imaging technique, which is non-destructive and has the advantages of fast speed and nice effect, can be used for the measurement of real-time of seeds.

GaAs nanowires growth on GaAs(1 1 1)B substrates by Au-assisted MBE with solid As4 source were investigated as function of group III and V flux, growth time and growth temperature. It was found that the axial, radial growth and crystal structure of NWs could be controlled through tuning growth parameters. The optimal strategies for one dimensional nano-scale devices fabrications were also suggested.

Nanocrystalline thin films of copper nitride were grown on Si (1 0 0) wafers at a low substrate temperature by reactive magnetron sputtering of Cu target with the mixture of nitrogen and argon. The influence of nitrogen deficiency upon the structural, optical and electrical properties of as-deposited films was investigated. X-ray diffraction confirms the presence of cubic Cu3N and Cu biphases irrespective of carefully optimized processing parameters. With a Cu content approaching the stoichiometry for Cu3N, the films assume a smooth morphology with densely-packed nanocrystallites of about 40–60 nm in size. Those deposits containing more than 79% Cu are metallic conductors with excellent electrical conductivity via a percolation mechanism, whereas the slightly substoichiometric Cu3N films show a typical behavior of deficit semiconductor, with an optical gap of about 1.85 eV as revealed by photoreflectance measurement. All the observations are discussed in terms of nitrogen reemission from the growing film.

Negative water balance in soil can lead to soil desiccation and subsequent the formation of a dried soil layer (DSL). Essential progress on DSL temporal change has been hampered by difficulty in collecting deep soil water samples (i.e. > 1000 cm), which are necessary to quantify the real extent of DSL. We collected soil samples up to a depth of 1800 cm and investigated the evolution of soil water content (SWC) and DSL under three vegetation types (C. korshinskii, R. pseudoacacia, apple) in three zones (Ansai, Luochuan, and Changwu) of the Chinese Loess Plateau. As plant growth age increased, SWC, available soil water (ASW), SWC within DSL (DSL-SWC), and quantity of water deficit for DSL (DSL-QWD) showed similar change trends of decreasing at first and then increasing, whereas DSL thickness (DSLT) showed an increasing trend over time. A turning point in soil water change was found for the three vegetation types. In Changwu zone, the turning point, both in and out of DSL, was corresponded to the 17-year-old apple orchard. The period from 9 to 17 yr was vital to maintain the buffering function of deep soil water pool and to avoid the deterioration of soil desiccation because the highest mean decline velocity of ASW and the maximum mean forming velocity of DSLT were 165 mm yr−1 and 168 cm yr−1, respectively. Significant correlations were found between DSLT and growth age and root depth, and between DSL-QWD and root depth, whereas mean DSL-SWC had no significant correlation with either growth year or root depth. Soil water condition was highly dependent on the growth year of the plants. This information provides pertinent reference for water resource management in the Chinese Loess Plateau and possibly in other water-limited regions in the world.

Zn1−xCdxO films (0⩽x⩽0.179) were grown on Si (001) substrates at 750°C with a radio-frequency reactive magnetron sputtering method. Difference between the photoluminescence (PL) spectra taken at room temperature (RT) and at 12K is reported and is deduced to be the result of PL emission from the ZnCdO phases with wurtzite and zinc blende structures. It is also found that the RT PL intensity is in inverse proportion to the carrier concentration in the films. Cd incorporation results in the transform of conductivity from p type to n type and a decrease of carrier mobility.

Bright blue-violet photoluminescence centered at 428nm was obtained in amorphous Si-in-SiNx thin films prepared in a cyclic growth mode on cool substrates by plasma-enhanced chemical vapor deposition, in which the typical size of the silicon particles has been brought down to ∼1.80nm and the number density amounts to 1.07×1013cm2. A maximum external quantum efficiency over 3.0% was measured in the as-deposited samples. Time-resolved photoluminescence spectra revealed decay times within nanosecond even at room temperature, disclosing a fast recombination dynamics in this amorphous system. The excellent efficiency can be attributed to a better passivation of the silicon particles—hence, the conventional rapid thermal annealing has a negligible effect on the photoluminescence intensity—and also to an improved transparency of the film by cyclic growth. The high-efficiency, tunable wavelength and nanosecond decay time at room temperature, achieved via a low-temperature process without invoking any posttreatmen...