ABSTRACT
In recent years, we found that Hishimonus lamellatus Cai et Kuoh is a potential vector of jujube witches'-broom phytoplasma. However, little is known about the anatomy and histology of this leafhopper. Here, we examined histology and ultrastructure of the digestive system of H. lamellatus, both by dissecting and by semi- and ultrathin sectioning techniques. We found that the H. lamellatus digestive tract consists of an esophagus, a filter chamber, a conical midgut and midgut loop, Malpighian tubules, an ileum, and a rectum. Furthermore, both the basal region of the filter chamber epithelium and the apical surface of the midgut epithelium have developed microvilli. We also identify the perimicrovillar membrane, which ensheaths the microvilli of midgut loop enterocyte, and the flame-like luminal membrane, which covers the microvilli of the conical midgut epithelium. In addition, H. lamellatus has the principal and accessory salivary glands. Our observations also showed that the endoplasmic reticulum, mitochondria, and secretory granules were all highly abundant in the secretory cells of the principal salivary glands, while the accessory glands consist of only one ovate or elbow-like acinus. We also briefly contrast the structure of the gut of H. lamellatus with those of other leafhopper species. These results intend to offer help for the future study on the histological and subcellular levels of phytopathogen-leafhopper relationships, including transmission barriers and the binding sites of pathogens and other microorganisms within their leafhopper vectors.
Subject(s)
Hemiptera/ultrastructure , Malpighian Tubules/ultrastructure , Animals , Gastrointestinal Tract/ultrastructure , Microscopy, Electron, Transmission , Salivary Glands/ultrastructureABSTRACT
Cesium lead halide perovskite nanocrystals (NCs) possess excellent optical properties at visible wavelengths with great promise for applications in luminous display fields. We demonstrate a method to modify the surface ligand passivation of perovskite NCs for enhanced colloidal stability and emitting properties by incorporating didodecyl dimethyl ammonium bromide (DDAB). The photoluminescence quantum yield of the NC solution was improved to 96% from 70% and the perovskite film showed fewer trapped sites and enhanced carrier transport ability. The thus fabricated electroluminescent perovskite NC-LEDs exhibited a bright luminance of 11 990 cd m-2, corresponding to 4-times improved external quantum efficiency (EQE), compared to the control device using regular NCs without DDAB.
ABSTRACT
The high photoluminescence quantum yield, wide color tunability and narrow bandwidth of perovskite nanocrystals make them favorable for light source and display applications. Here, highly transparent green-light-emitting devices (LEDs) using inorganic cesium lead halide perovskite nanocrystal films as the emissive layer are reported. The effect of multilayered nanostructured transparent electrode on optical properties and performance within the LEDs is investigated by fine tuning layer thickness. The results show that the light transmission in visible region can be enhanced with this nanostructured film. These LEDs exhibited a high transmittance (average 73% over 400-700 nm) and high brightness of 2640 and 1572 cd m-2 for indium-doped tin oxide (ITO) cathode and MoO x /Au/MoO x anode sides, respectively.
ABSTRACT
Recently, near-infrared light-emitting diodes (NIR LEDs) based on PbSe quantum dots (QDs) have attracted considerable attention due to their facilely tunable emission wavelength, as well as high quantum yield. However, the low external quantum efficiency (EQE) of these LEDs has restricted their actual applications because of the non-radiative recombination caused by the aggregation in the solid-state QD films. Therefore, we proposed in this work to employ the liquid-type structure in NIR LEDs base on PbSe QDs, which exhibited the main advantages relying on the fact that the liquid structure could prevent the active layer from self-aggregation and improve the device stability. The emission intensity of these NIR LEDs was optimized by tuning the concentration of PbSe QDs. Besides, the radiation power of PbSe QD-based devices with different emission wavelengths was analyzed under different biases, and the maximum EQE of NIR LEDs was confirmed to be 5.3%. This result represents the highest record among the reported NIR QD-LEDs, indicating this kind of liquid-type NIR LEDs is promising for commercial applications.
ABSTRACT
With good electrical conductivity, optical transparency, and mechanical compliance, graphene films have shown great potential in application for photovoltaic devices as electrodes. However, photovoltaic devices employing graphene anodes usually suffer from poor hole collection efficiency because of the mismatch of energy levels between the anode and light-harvesting layers. Here, a simple solution treatment and a low-cost solution-processed molybdenum oxide (MoOx) film were used to modify the work function of graphene and the interfacial morphology, respectively, yielding highly efficient hole transfer. As a result, the graphene/MoOx anodes demonstrated low surface roughness and high electrical conductivity. Using the graphene/MoOx anodes in PbSe nanocrystal solar cells, we achieved 1 sun power conversion efficiency of 3.56%. Compared to the control devices with indium tin oxide anodes, the graphene/MoOx-based devices show excellent performance, demonstrating the great potential of the graphene/MoOx anodes for use in optoelectronics.
ABSTRACT
Colloidal PbSe QDs were prepared with the particle size of 3. 6, 5. 1 and 6. 0 nm, and the temperature-dependent optical properties of colloidal PbSe QDs were investigated. At the room temperature, the experiment showed that there is red shift with increasing temperature; photoluminescence spectra of large size colloidal PbSe QDs is blue shifted with increasing temperature. Proposed a temperature detection method of integrated circuit was proposed based on photoluminescence spectra of colloidal PbSe QDs. The method for temperature detection includes colloidal PbSe quantum dots deposited on the surface of the printed circuit board, colloidal PbSe quantum dots of the surface are excited by the laser and infrared spectrometer receives photoluminescence spectra. Image acquisition system used for micron scale areas of temperature detection collects a tiny and specific areas imaging in the surface of chip. Experiments showed that the measurement accuracy is ±3 °C and the relative error is less than 5%.
ABSTRACT
We realized white light-emitting diodes with high color rendering index (85-96) and widely variable color temperatures (2805-7786 K) by combining three phosphors based on carbon dots and polymer dots, whose solid-state photoluminescence self-quenching was efficiently suppressed within a polyvinyl pyrrolidone matrix. All three phosphors exhibited dominant absorption in the UV spectral region, which ensured the weak reabsorption and no energy transfer crosstalk. The WLEDs showed excellent color stability against the increasing current because of the similar response of the tricolor phosphors to the UV light variation.
ABSTRACT
Single layer graphene was employed as the electrode in quantum dot-light emitting diodes (QD-LEDs) to replace indium tin oxide (ITO). The graphene layer demonstrated low surface roughness, good hole injection ability, and proper work function matching with the poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) layer. Together with the hole transport layer and electron transport layer, the fabricated QD-LED showed good current efficiency and power efficiency, which were even higher than an ITO-based similar device under low current density. The result indicates that graphene can be used as anodes to replace ITO in QD-LEDs.
ABSTRACT
Multigas sensing is highly demanded in the fields of environmental monitoring, industrial production, and coal mine security. Three near-infrared emission wavelengths from PbSe quantum dots (QDs) were used to analyze the concentration of three gases simultaneously through direct absorption spectroscopy, including acetylene (C2H2), methane (CH4), and ammonia (NH3). The corresponding lower detection limits for the three gases were 20, 100, and 20 ppm, respectively, with an accuracy of 2%. This study demonstrates that QDs with tunable emissions have great potential for simultaneous and uninterfered multiplex gas analysis and detection due to the advantages of the easy tunability of multiplex emitting wavelengths from QDs.
ABSTRACT
This work describes a micrometer resolution and plane-array temperature-sensing method using the photoluminescence (PL) of ZnCuInS/ZnSe/ZnS quantum dots (QDs). Heavy-metal-free QDs were directly deposited on a printed circuit board to analyze the surface temperature of the devices on the board. An optical fiber monochromator and a high-powered microscope were employed to fabricate a system which could collect temperature-dependent QD emissions from the micrometer area for the temperature measurements. This system realizes the imaging of the surface temperature distribution in the planar micrometer area. Temperature sensitivity of the PL intensity reached 0.66% °C(-1), and the relative error was less than 2%.
ABSTRACT
ZnCuInS/ZnSe/ZnS quantum dots were non-toxic and heavy-metal free semiconductor nanocrystals. In the present paper, ZnCuInS/ZnSe/ZnS core/shell/shell quantum dots were prepared with the particle size of 3.3, 2.7 and 2.3 nm. The photoluminescence of ZnCuInS/ZnSe/ZnS quantum dots with different size were measured, and the wavelength of peak was blue-shifted with decreasing the diameter. The wavelength of absorption peaks and photoluminescence peaks were 510 nm, 611 nm (3.3 nm), 483 nm, 583 nm (2.7 nm) and 447 nm and 545 nm(2.3 nm). The obvious size-dependence of ZnCuInS/ZnSe/ZnS quantum dots was shown. The Stokes shifts of ZnCuInS/ZnSe/ZnS quantum dots were 398 meV (3.3 nm), 436 meV (2.7 nm) and 498 meV (2.3 nm). Such large Stokes shifts indicate that the emission should be ascribed to the defect-related recombination. The temperature-dependent photoluminescence of ZnCuInS/ZnSe/ZnS quantum dots with the particle size of 3.3 nm were measured. The wavelength of peaks was red-shifted with increasing temperature and the intensity of photoluminescence spectra was decreased with increasing temperature. Therefore, the emission was concluded to be the transition from the conduction band to defect state.
ABSTRACT
We have studied the optical properties of PbSe colloidal quantum dot-solution filled hollow core multimode silica waveguides as a function of quantum dot-solution concentration, waveguide length, optical pump power and choice of organic solvent in order to establish the conditions to maximize near infrared spontaneous emission intensities. The optical performance was compared and showed good agreement with a simple three level system model for the quantum dots confined in an optical waveguide. Near infrared absorption-free solvent of tetrachlorethylene was confirmed to be a good candidate for the waveguide medium due to the enhancement of output intensity from the liquid-core fiber compared to the performance in toluene-based fiber. This approach demonstrates a useful method for early characterization of quantum dot materials in a waveguide test-bed with minimal material processing on the colloidal nanoparticles.
ABSTRACT
Carbon-dot based light-emitting diodes (LEDs) with driving current controlled color change are reported. These devices consist of a carbon-dot emissive layer sandwiched between an organic hole transport layer and an organic or inorganic electron transport layer fabricated by a solution-based process. By tuning the device structure and the injecting current density (by changing the applied voltage), we can obtain multicolor emission of blue, cyan, magenta, and white from the same carbon dots. Such a switchable EL behavior with white emission has not been observed thus far in single emitting layer structured nanomaterial LEDs. This interesting current density-dependent emission is useful for the development of colorful LEDs. The pure blue and white emissions are obtained by tuning the electron transport layer materials and the thickness of electrode.
ABSTRACT
PbSe quantum dots (QDs) were employed as real-time and on-chip temperature sensors to monitor the surface temperature of GaN LED chips. The temperature-dependent photoluminescence spectra were achieved and confirmed to be a good method for surface temperature sensing in a micro- to nano-region. The nanosized QD sensors did not influence the LED emission spectrum due to their infrared emission and little absorption. The surface temperature of GaN LED chips was analyzed at different working times and voltages. The temperature sensitivity characterized by the photoluminescence peak position of PbSe QDs was found to be 0.15 nm °C(-1) in a range of 30-120 °C and the precision was determined to be ± 3 °C. The QD surface temperature sensors were confirmed to have good reversibility and repeatability.
ABSTRACT
In the present paper colloidal PbSe nanocrystals were prepared with the particle size of 3.8 and 5.8 nm, and the temperature- dependent optical properties of colloidal PbSe nanocrystals were investigated. The experimental data show that the band gap, photoluminescence peak wavelength, photoluminescence intensity and full width at half-maximum of colloidal PbSe nanocrystals will change with variations in temperature and size at room temperature. The band gap of colloidal PbSe nanocrystals with the particle size of 3.8 nm shifts towards red when the temperature increases. However, the blue shift occurs when the particle size is 5.8 nm. The photoluminescence intensity of colloidal PbSe nanocrystals drops and the full width at half-maximum will increases with the increase in temperature.
ABSTRACT
A new method is proposed to calculate the Stark shift induced by surface dielectric effect in colloidal nanocrystals. The effective mass approximation model is revised according to quantum confined dielectric effect. LUMO (the lowest unoccupied molecular orbital), HOMO (the highest occupied molecular orbital), band gap and Stark shift are calculated in CdSe and PbSe nanocrystals that bear significantly different physical properties. The calculated results fit well with the experimental data. The calculation of dielectric effect-induced Stark shift indicates that the quantum confined dielectric effect in PbSe and CdSe nanocrystals is size- and temperature-dependent, which is more notable in PbSe nanocrystals with a narrower band gap and results in the gentle variation of quantum confinement energy with particle size.
ABSTRACT
In the present paper ZnCuInS/ZnS core/shell quantum dots were prepared with the particle size of 3.2 nm. Its radiation is based on the donoracceptor pair transitions, not the band edge emission. According to the measurement of photoluminescence spectrum emitted by ZnCuInS/ZnS core/shell quantum dots, the emitting peak of 620 nm and the full width at half-maximum of 95 nm were achieved as red emitter; meanwhile, organic poly(N, N'-bis(4-butylphenyl)-N, N'-bis(phenyl) benzidine) (Poly-TPD) film was deposited and used as cyan-emitter with the peak of 480 nm. Two structures of Poly-TPD were analyzed and discussed according to the photoluminescence spectrum. Two wavelengths are complementary color. Therefore, two films were deposited one by one as bilayer emitter to obtain the complementary emission. After the suitable bias was applied on the films, the white emission was achieved with the Commission Internationale de l' Eclairage (CIE) chromaticity coordinates of (0.336, 0.339) and color rendering index of 92. Therefore, the bilayer-structure is a promising candidate for white light emitting diodes fabrication.
ABSTRACT
A method of recognizing the visible spectrum of micro-areas on the biological surface with cascade-connection artificial neural nets is presented in the present paper. The visible spectra of spots on apples' pericarp, ranging from 500 to 730 nm, were obtained with a fiber-probe spectrometer, and a new spectrum recognition system consisting of three-level cascade-connection neural nets was set up. The experiments show that the spectra of rotten, scar and bumped spot on an apple's pericarp can be recognized by the spectrum recognition system, and the recognition accuracy is higher than 85% even when noise level is 15%. The new recognition system overcomes the disadvantages of poor accuracy and poor anti-noise with the traditional system based on single cascade neural nets. Finally, a new method of expression of recognition results was proved. The method is based on the conception of degree of membership in fuzzing mathematics, and through it the recognition results can be expressed exactly and objectively.
Subject(s)
Neural Networks, Computer , Pattern Recognition, Automated/methods , Spectrum Analysis/methodsABSTRACT
By using community structural characteristic indices and principal component analysis, this paper studied the community structure and its dynamics of predatory arthropod in the jujube orchards intercropped with Astrugalus complanatus, Trifolium repen, Lotus comiculotus, and Medicago sativa. The results showed that in all test jujube orchards, spider and predatory insects were the predominant components of the predatory arthropod community, and their relative abundances were 48.3% - 52.7% and 38.8% - 44.4% , respectively. There were significant differences (P < 0.05) in the mean density, diversity, and evenness of the most common predatory arthropod groups in the jujube orchards intercropped with different herbage species, with the sequence of intercropped with Lotus comiculotus > Medicago sativa > Astrugalus complanatu > Trifolium repens, but for dominant concentration index, the sequence was intercropped with Trifolium repens > Astrugalus complanatu > Medicago sativa > Lotus comiculotus. The average density of predatory spiders was significant higher (P < 0.05) than that of predatory insects in all test jujube orchards. The individuals of Coccinellidae, Pentatomidae, inoccllidae, Chrysopidae, Thomisidae, Araneidae and Phytoseiidae played the dominant role in the community.
Subject(s)
Agriculture/methods , Arthropods/physiology , Poaceae/growth & development , Predatory Behavior/physiology , Ziziphus/parasitology , Animals , Arthropods/growth & development , Ecosystem , Population Dynamics , Ziziphus/growth & developmentABSTRACT
We measured NIR spectrum of VC yinqiao tablets with spectral instrument, analyzed the contents of acetaminophen and vitamin C in the VC yinqiao tablets with principal component analysis (PCA) and Linear Neural Network, and discussed the choice of principal component number and ANN's parameters affecting the network. To compare arithmetic performance, the authors also processed the spectral data with partial least squares and PCA-BP neural network. Compared with other two data process methods, the experiment and the result of data process showed that the PCA-linear neural network possess the best forecasting precision.
