Ultraviolet-visible Region Research Articles

Sandwich-like GaN/MoSe2/GaN heterostructure nanosheet: A First-principle study of the structure, electronic, optical, and thermodynamical properties

Due to the wide range of applications of two-dimensional heterostructures in photocatalysis, electronics, and optoelectronics, research on these materials has received considerable interest. This paper provides a systematic understanding of the sandwich-like GaN/MoSe2/GaN heterostructure nanosheet to explore geometrical structures and electronic, optical, and thermodynamical properties using a density functional theory. As per the band structure analysis, the heterostructure is a type-II semiconductor with a direct band-gap of 1.36 eV. The optical properties of the nanosheet in different polarization directions were studied. The work function of the heterostructure shows 5.10 eV, which is smaller than the constituent nanosheets. The phonon dispersion curves do not show a negative acoustic band that shows the stability of the studied nanosheets. The alignment of the band structures, charge difference and generated electric field at the vdW heterostructure interface advantage constrain photogenerated electron-hole recombination, enabling improved optical characteristics in the ultraviolet-visible and near-infrared spectroscopy regions, indicating the studied heterostructure can be employed in photovoltaic, photocatalytic, and optical devices.

Ultra-Broadband Random Laser and White-Light Emissive Carbon Dots/Crystal In-Situ Hybrids.

The continuous white-light emission of carbon dots (CDs) can be applied to producing multicolor laser emissions by one single medium. Meanwhile, the solid-state emission greatly contributes to its practical application. In this work, a strategy to realize the in-situ hybridization of silane-functionalized CDs (SiCDs) and 1,3,5-benzenetricarboxylic acid trimethyl ester (Et3BTC) by a one-pot solvothermal method is reported. Significantly, the SiCDs/Et3BTC hybrid crystals exhibit ultra-broadband random laser emission over the near ultraviolet-visible region under 265nm nanosecond pulsed laser excitation. The wavelength region of laser emission is achieved from 315 to 600nm within an emission band of CDs-based materials. It is worth noting that the wavelength range of the laser is wider than the previously reported works. It is proposed that the continuous white-light emission of SiCDs caused by multiple fluorescence centers mainly gives rise to the broadband random laser emission. Moreover, the crystals are conducive to forming resonance and realizing solid-state laser emission. This in-situ method is expected to enable a more convenient, cheaper, and greener approach to prepare luminescent hybrids for application in multicolor laser displays, multi-level laser anti-counterfeiting, supercontinuum light sources, and so on.

A novel two-dimensional transition metal dichalcogenide as water splitting photocatalyst with excellent performances.

With the rising demand for renewable energy, photocatalysts are considered the most promising solution to harness solar energy, and the search for photocatalysts with excellent performances remains an urgent task. Here, based on density functional theory (DFT), the photocatalytic properties of MoWS4 are systematically investigated. The MoWS4 monolayer and bilayer are demonstrated as semiconductors with indirect band gaps of 2.01 and 1.48 eV. Moreover, they exhibit high and anisotropic light absorption coefficients of up to ∼105 cm−1 in the visible-ultraviolet region. The intrinsic band edge positions could fully satisfy the redox potentials of water without any external adjustment. The electron mobility of MoWS4 monolayer is 557 cm2 V−1s−1, which is seven times higher than MoS2 monolayer. Hence, MoWS4 can be regarded as a promising 2D photocatalyst candidate for water splitting.

Near infrared optically responsive Ag-Cu bimetallic 2D nanocrystals with controllable spatial structures

The optical properties of cost-effective Ag-Cu bimetallic nanocrystals, with synergistically enhanced catalytic and biological activities, are limited within ultraviolet–visible region due to lack of morphology control. In order to overcome this constraint, two-dimensional (2D) Ag-Cu bimetallic heterostructures were designed and synthesized by a seed-mediated colloidal growth method. The conformal Cu domain was epitaxially deposited on Ag nanoplates with different spatial configuration under retention of their 2D shape. Both of the 2D Ag-Cu core@shell and Janus structures display tunable localized surface plasmon resonance from visible to near infrared regions. The results of catalytic reduction of 4-nitrophenol show that the 2D Ag-Cu core@shell structure has better synergistic catalytic performance than Janus structure and Ag plates. In addition to surface-related synergistically enhanced bactericidal performance, their antibacterial effect can also be significantly enhanced by near infrared light irradiation. These results indicate that 2D Ag-Cu heterostructures can benefit from both synergistically improved surface activity and great optical responsive characteristics.

Emerging exotic properties of two-dimensional ternary tetrahexagonal BCN: Tunable anisotropic transport properties with huge excitonic effects for nanoelectronics and optoelectronics

A two-dimensional ternary tetrahexagonal BCN monolayer (th-BCN) is designed by applying Stone-Wales transformation to its pentagonal counterpart (p-BCN). Using first-principles calculations, we examine the dynamical, mechanical, thermal, and environment stability of th-BCN. The monolayer exhibits superior anisotropic electronic and optical properties compared to its counterparts (the domains of C and BN in the tetrahexagonal network and p-BCN). Direct band gap of 3.05 eV and excellent band edge alignment with the oxidation and reduction reactions of water heralds the use of th-BCN in photocatalytic water splitting. The band gap energy and band edge positions can be further adjusted by strain. The anisotropic high carrier mobility of th-BCN improves fast carrier separation and low recombination rate. The electronic transport direction can be easily controlled by strain engineering. For instance, one can rotate the preferred transport direction of hole by 90° with a very small uniaxial strain. Many-body effects beyond DFT reveal that the monolayer has strong light-harvesting capability (105cm−1) in the visible-ultraviolet region and exhibits strong excitonic effects with large excitonic binding energy of 0.98 eV. All these appealing properties make th-BCN a promising and tunable anisotropic 2D material for nanoelectronic and optoelectronic applications.

Characterization of WO3 thin films deposited by spray pyrolysis technique and its role in gas sensing

The work investigated in this paper focused on the fabrication of WO3 films by the spray pyrolysis technique, and different analyses were made to find optimized samples for studying properties suitable for the application of gas sensing. The substrate temperature is the most important parameter among other spray parameters for the synthesis of thin films hence WO3 thin films were deposited on glass substrates by maintaining the substrate temperature at 350 ºC, 450 ºC, 550 ºC, and 650 °C using compressed air as a carrier gas. The influence of the substrate temperature on the structural, morphological, compositional, and optical properties of the WO3 thin films has been justified using XRD data. Good and enhanced crystallinity is observed for the film deposited at a substrate temperature of 550 ºC. The nonconventional properties were studied by different investigations and confirmed by past research work. The manipulation of surface morphology with the different deposition temperatures is monitored. Only the characteristic peaks of W and O are present in the fabricated WO3 thin films. The optical activity of about 70 to 80 % of the selected sample in the visible region (300 to 1200 nm) is found. The selective absorption activity of light in the ultraviolet region and visible region is checked. The obtained IR bands confirmed the inter bridge stretching and bending modes of W-O and O-W-O. A high response towards ammonia compared to other test gases is exhibited. The repeatability of WO3 towards NH3 over three periodic sensing cycles, response, and recovery time has also been discussed. From all the characteristic studies, it has been suggested that the fabricated WO3 thin films have been used in the health care field to detect the toxic NH3 gas

Study of the structural, electronic, mechanical, electro-thermal and optical properties of double perovskite structures Cs2SbAgX6, (X = I, Br, or Cl)

In the double perovskites structures, Cs2SbAgX6, X is I, Br, or Cl, the structural, electronic, thermodynamic, thermoelectric and optical, properties have been investigated by using the density functional theory (DFT) correction method. The XRD structural study exhibits that the double perovskite structures are stable in the cubic phase structures. Elastic parameters reveal all structures to be very hard and ductile in nature. The energy band profiles display indirect band-gap of semiconductor behavior for the structures Cs2SbAgX6; X is Cl or Br, while exhibiting metallic behavior of the structure Cs2SbAgI6. The thermoelectric transport properties were verified in the temperature range (5–1000) K, which includes electrical conductivity, thermal conductivity, Seebeck coefficients, and the figure of merit, ZT, for Cs2SbAgX6 structures. These structures exhibit high thermal conductivity with good Seebeck coefficients at room temperature. The semiconducting structure, Cs2SbAgBr6, has appropriate band gaps and best Seebeck coefficients; therefore, it has the best values of ZT reached 0.000 16 at 1000 K, which means the suitable structure for employment in thermoelectric and spintronic devices applications. The optical properties of these structures exhibit that the absorption effective region at the Visible-Ultraviolet region, therefore these materials are suitable in the applications of solar cells and optoelectronic devices.

Two-Dimensional Perovskite-Gated AlGaN/GaN High-Electron-Mobility-Transistor for Neuromorphic Vision Sensor.

The extraordinary optoelectronic properties and continued commercialization of GaN enable it a promising component for neuromorphic visual system (NVS). However, typical GaN‐based optoelectronic devices demonstrated to data only show temporary and unidirectional photoresponse in ultraviolet region, which is an insurmountable obstacle for construction of NVS in practical applications. Herein, an ultrasensitive visual sensor with phototransistor architecture consisting of AlGaN/GaN high‐electron‐mobility‐transistor (HEMT) and two‐dimensional Ruddlesden–Popper organic–inorganic halide perovskite (2D OIHP) is reported. Utilizing the significant variation in activation energy for ion transport in 2D OIHP (from 1.3 eV under dark to 0.4 eV under illumination), the sensor can efficiently perceive and storage optical information in ultraviolet–visible region. Meanwhile, the photo‐enhanced field‐effect mechanism in the depletion‐mode HEMT enables gate‐tunable negative and positive photoresponse, where some typical optoelectronic synaptic functions including inhibitory and excitatory postsynaptic current as well as paired‐pulse facilitation are demonstrated. More importantly, a NVS based on the proposed visual sensor array is constructed for achieving neuromorphic visual preprocessing with an improved color image recognition rate of 100%.

The Created Excellent Thermal, Mechanical and Fluorescent Properties by Doping Eu3+-Complex-Anchored Carbon Nanotubes in Polycyanate Resins.

In the blending process of the composites, the clustering of MWCNTs under high concentration leads to poor dispersion and difficult complexing with luminescent elements. Cyanate ester resins (CERs) have a brittle network structure when cured caused by a conjugation effect that forms a strong emission peak in the ultraviolet-visible region and quenches the luminescent elements of the fluorescent nanofillers. In this paper, by anchoring of the Eu complex (Eu(TTA)3Phen, ETP) on a surface of longitudinal split unzipped carbon nanotubes (uMWCNTs); fluorescent nanoparticles were prepared as ETP anchor unzipper carbon nanotubes (ETP-uCNTs). Dicyanate ester of bisphenol E (CER-E monomer) is cured to polycyanurate at a lower temperature to achieve a high conversion, promoting a uniform blend with ETP-uCNTs, providing the fluorescence environment with high color purity. Studies show the ETP-uCNTs solve the agglomeration of MWCNTs and improve the interface binding ability. Compared with the pure CER-E, the tensile strength, bending strength and impact strength of CER-E/0.8 wt.% ETP-uCNT hybrid nanocomposites are increased by 94.6%, 92.8% and 101.1%, respectively. The carbon residue rate of CER-E/ETP-uCNTs is up to 47.14% at 800 °C, the temperature of the maximum reaction rate decreases by 67.81 °C, and the partial absorption of ultraviolet light is realized between 200 and 400 nm.

Wavelength-Tunable Multispectral Photodetector With Both Ultraviolet and Near-Infrared Narrowband Detection Capability

The development of high-performance multispectral photodetector with narrowband and tunable spectral sensitivity is of importance but remains highly challenging to date. Here, we have reported on the fabrication of a Si Au/n-type Si/Au photodetector with tunable narrowband sensitivity not only in ultraviolet but also in near-infrared region, which is related to the controlled charge collection narrowing (CCN) mechanism. What is more, the negative response peak of the device can be readily tuned from 365 to 605 nm, and the positive response peak can be modulated from 938 to 970 nm when the bias varies from 0.1 to −0.1 V. In particular, the full-width at half-maximum is as small as 92 and 117 nm when the negative and positive response peaks approach the ultraviolet short wavelength end and near-infrared long wavelength end, respectively. The opposite polarity of the device responses in ultraviolet-visible and near-infrared regions renders the present Si photodetector potentially important in future multiple band optoelectronic systems.

Synthetic strategies for highly transparent and colorless polyimide film

AbstractPolyimide (PI) is one of the best engineering plastics with excellent thermal, mechanical, dielectric performance and chemical stability. Among various PI products, film is one of the most dominant types. If PI films are to be applied to optical devices and display equipment, it is necessary to improve their optical transparency in the ultraviolet–visible region. However, improving the optical transparency of PI films would affect their thermal performance including thermal and dimensional stability. Therefore, how to balance optical and thermal performance to obtain highly transparent PI films with the best overall performance becomes a focus of current research field. In this review, we categorize transparent PI films into highly transparent PI, transparent PI with high glass transition temperature (Tg) and transparent PI with low coefficient of thermal expansion (CTE) based on their optical and thermal properties. Then, we review research progress in the field of polymer molecular design including synthesis strategies and properties in recent 5 years, to inspire research ideas and elaborate on the possible ways to develop high‐performance, colorless and transparent PI materials.

Green synthesis of CuNb2O6 thin film using allium cepa as catalyst

ABSTRACT The objective of this study was to synthesize and characterize a novel green synthesis of copper niobate (CuNb2O6) thin film using copper (II) sulfate pentahydrate (CuSO4 · 5H2O), an organometallic precursor of bis(cyclopentadienyl) niobium (IV) dichloride (C10H10Cl2Nb), using Allium cepa as a catalyst. The synthesized thin film was characterized using the XRD, EDX, SEM FTIR, UVvis, and 4-point probe measurement. The XRD patterns of the thin film affirmed the formation of a pure monoclinic CuNb2O6 phase. Similarly, the SEM images illustrated the formation of the film and the different film microstructures. The EDX revealed that the thin film consisted of copper (Cu), niobium (Nb), and oxygen (O) elements. The thin film, however, possessed broad absorption in the Ultraviolet-Visible (UV–Vis) region with an absorption edge at 340 nm and an optical bandgap evaluated to be 3.18 eV. Also, the fabricated film’s transmittance ranged between 40% and 55%. A Raman shift of 690 cm−1 was identified at the CuNb2O6 film. The results obtained from the FTIR analysis demonstrated characteristic IR bands at 608 cm−1 and 940 cm−1 which indicated the formation of the Cu-O and Nb-O-Nb bonds. With the rising temperature, an increase in conductivity and a decrease in resistivity were noticed from the plots. This indicated that the synthesized CuNb2O6 thin film exhibited good semiconducting qualities. The prepared CuNb2O6 thin film thus possesses improved electrical properties and can therefore be effectively utilized in photovoltaic solar cells.

Solution-Processed Ternary Perovskite-Organic Broadband Photodetectors with Ultrahigh Detectivity.

Room temperature operated, solution-processed ultrasensitive broadband photodetectors are widely used in various industrial companies in the scientific and medical sectors. Herein, we report solution-processed ultrahigh detectivity broadband photodetectors based on the ternary perovskite-organic composites. To ensure the photodetector based on perovskites has a photoresponse from the ultraviolet-visible to the near-infrared (NIR) region, low optical gap n-type conjugated organic molecules are incorporated with the three-dimensional (3D) perovskites mixed with the two-dimensional (2D) perovskites to form the ternary perovskite-organic composites, which possess an extended spectral response up to the NIR region and superior film characteristics compared to the 2D-3D mixed perovskite composites. Moreover, the photodetectors based on the ternary perovskite-organic composites exhibit enhanced photocurrent and suppressed dark current compared to those based on the 2D/3D mixed perovskite composites. As a result, at room temperature, the photodetectors based on the ternary perovskite-organic composites exhibit a spectral response from 375 to 1000 nm, whereas the photodetectors based on the 2D-3D mixed perovskite composites exhibit a spectral response from 375 to 800 nm. Furthermore, the photodetectors based on the ternary perovskite-organic composites have a photodetectivity over 1015 cm Hz1/2 W-1 (Jones) in the ultraviolet-visible region and over 1013 Jones in the NIR region, a linear dynamic range over 110 dB, and a fast response time. All these results demonstrate that we developed a facile way to realize uncooled solution-processed ultrahigh detectivity broadband photodetectors based on the ternary perovskite-organic composites.

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Selective hydroboration of terminal alkynes catalyzed by heterometallic clusters with uranium–metal triple bonds

Photoelectrocatalytic hydrolysis of ammonia borane by electrochemical deposited cuprous oxide on titanium dioxide nanotube arrays

Photoelectrocatalytic hydrolysis of ammonia borane (AB) is a promising technique for producing hydrogen gas (H 2 ) in the presence of an appropriate photocatalyst under light irradiation and bias. The application of cuprous oxide on titanium dioxide nanotube arrays (Cu 2 O/TNA) for the photoelectrocatalytic hydrolysis of AB was studied. Cu 2 O/TNA exhibited a spectral response in the ultraviolet–visible region and an onset wavelength of 600 nm. With AB in an electrolyte, Cu 2 O/TNA exhibited a significant increase in its photocurrent spectral response at a bias of 0.1 V versus Ag/AgCl. The H 2 generation rate by photoelectrocatalysis (under 5-mW cm −2 irradiation at 455 nm; bias of 0.1 V vs . Ag/AgCl) was 0.018 μmol s −1 cm −2 , which was twice that by photocatalysis and four times those by catalysis and electrocatalysis; a Faradaic efficiency of 77% (corresponding to the oxidation reaction of AB) was also observed. Hence, Cu 2 O/TNA is an efficient photoanode for photoelectrocatalytic hydrolysis of AB. • Cu 2 O/TNA is a promising photoanode for photoelectrocatalytic hydrolysis of AB. • Cu 2 O/TNA performed a significant spectral response at 0.1 V versus Ag/AgCl. • H 2 generation rate by PEC was twice that by PC and four times those by C and EC. • The reaction at 0.1 V versus Ag/AgCl corresponded to the oxidation reaction of AB.

Substituent effects on the UV-visible spectrum and excited electronic states of dithiocarboxylates.

The absorption spectra of a series of dithiocarboxylates were investigated in the ultraviolet-visible region. Two questions that this study aimed to address were as follows: (1) What transitions give rise to the features in the electronic spectra? And (2) what are the long- and short-range substituent effects on the absorption spectra? A series of 11 dithiocarboxylates were prepared as organic soluble salts. Time-dependent density functional theory (TDDFT) was used to calculate excited state energies and oscillator strengths of electronic transitions. TDDFT at the CAM-B3LYP/def2-TZVPD level of theory predicts two low-energy n → π* transitions and two π → π* transitions at higher energy, consistent with the experimental spectra. This state ordering and density is in contrast to the better studied thiocarbonyls for which only two transitions within the singlet manifold appear in the UV-visible region. For derivatives of dithiobenzoate, the energy of the three lowest energy states are insensitive to changes to substituents para to the dithiocarboxylate group. In contrast, the energy of the highest ππ* state varies by 0.78eV. This work shows that the results of TDDFT calculations can be used to predict the electronic absorption spectra of dithiocarboxylates, providing a useful tool for designing dithiocarboxylate light absorbers.

Synthesis, Application and Antimicrobial Activity of New Acid Dyes Based on 3-Amino-2-thioxo-4-thiazolidinone Nucleus on Wool and Silk Fabrics.

This paper aims to synthesize and apply dye and antimicrobial to four new acid dyes based on derivatives of N-Amino rhodanine as a chromophoric group. Then, these dyes are used in dyeing silk and wool which have good lightfastness, and are also excellent for washing, rubbing and sweating fastness. Also, we measure antimicrobial susceptivity of silk and wool fabrics to Gram-negative and Gram-positive bacteria. The new synthetic acid dyes, which have antimicrobial susceptivity to gram-negative and gram-positive bacteria, are mostly used on silk and wool fabrics which are excellent for lightfastness, washing, rubbing and sweating fastness. The present studies aimed at synthesis, characterization and antimicrobial susceptivity to gramnegative and gram-positive bacteria. The infra-red spectrum was recorded using an Infra-red spectrometer, Perkin Elmer/1650 FTIR. The 1H-NMR spectra were recorded using a Varian 400MHz spectrometer. The absorbance of the dyes was measured in the ultraviolet-visible region between 300 and 700 nm by a UNICAM UV spectrophotometer. The dye uptake by wool and silk fabrics was measured using a Shimadzu UV-2401PC (UV/V is spectrophotometer at λmax) before and after dyeing. The produced dyes were found to have a good antimicrobial susceptivity to a variety of bacteria. The compounds a1, b1, a2 &b2 show good antimicrobial activity toward gramnegative (E. coli), gram-positive (S. aurous) bacteria. The data showed that exhaustion and fastness activities of silk and wool dyed fabrics were both very high. In this work, we prepared newly synthesized acid dyes based on 3-Amino-2-thioxo-4- thiazolidinone derivatives and used them for dyeing wool and silk fabrics. Both synthetic dyes have shown good lightfastness and fastness properties. Also, all dyes have shown a good antimicrobial effect.

A possible explanation for the blue spectral slope observed on B-type asteroids

In an effort to better understand the role dark material plays in the reflectance spectra of carbonaceous asteroids, we performed laboratory studies focusing on quantifying how the addition of relevant dark material (graphite, magnetite and troilite) can alter the ultraviolet-visible and near-infrared spectrum of a neutral silicate mineral. We find that addition of graphite, magnetite and troilite all darken the reflectance spectrum of forsterite and cause the spectral slope to decrease (become blue). These spectral changes can be caused by both nm- and μm-sized grains. In the ultraviolet-visible region, we find that graphite is most efficient at altering the spectral slope, while in the near-infrared, magnetite is the most efficient. At all wavelengths studied, graphite is the most efficient at darkening our sample spectrum. However, the observation that troilite also alters the slope and albedo of our samples suggests that the spectral changes caused by magnetite and graphite may not be unique. In addition, we find that the spectral slopes in our mixtures compare generally well to what has been observed on Bennu suggesting that a significant portion of fine-grained dark material, including sulfides, present in the regolith can cause the observed negative (blue) slope found on B-type asteroids.

Ultrasensitive Near-Infrared Circularly Polarized Light Detection Using 3D Perovskite Embedded with Chiral Plasmonic Nanoparticles.

Chiral organic ligand‐incorporated low‐dimensional metal‐halide perovskites have received increasing attention for next‐generation photodetectors because of the direct detection capability of circularly polarized light (CPL), which overcomes the requirement for subsidiary optical components in conventional CPL photodetectors. However, most chiral perovskites have been based on low‐dimensional structures that confine chiroptical responses to the ultraviolet (UV) or short‐wavelength visible region and limit photocurrent due to their wide bandgap and poor charge transport. Here, chiroptical properties of 3D Cs0.05FA0.5MA0.45Pb0.5Sn0.5I3 polycrystalline films are achieved by incorporating chiral plasmonic gold nanoparticles (AuNPs) into the mixed Pb—Sn perovskite, without sacrificing its original optoelectronic properties. CPL detectors fabricated using chiral AuNP‐embedded perovskite films can operate without external power input; they exhibit remarkable chirality in the near‐infrared (NIR) region with a high anisotropy factor of responsivity (g res) of 0.55, via giant plasmon resonance shift of chiral plasmonic AuNPs. In addition, a CPL detector array fabricated on a plastic substrate demonstrates highly sensitive self‐powered NIR detection with superior flexibility and durability.

A New Fluorescent Chemosensor for Selective and Sensitive Detection of Mn<sup>2+</sup> in Acidic Medium

Recently, fluorescent sensors have attracted considerable attention in their sensitive and selective determination of heavy metal ions in the aqueous acidic medium due to their advantages such as low cost and easy handling. In this study, the bathocuproine (BCP) compound was used as a fluorescent chemosensor. The selectivity and sensitivity of BCP have been investigated against some metal ions of biological and environmental importance. The results obtained from the ultraviolet-visible region (UV-vis.) and the fluorescence spectroscopy experiments revealed that the BCP sensor showed selectivity and sensitivity only to Manganese (II) ions in the experimental conditions studied. In addition, the binding stoichiometry of BCP and Mn2+ was determined to be 1:1 by the Benesi-Hildebrand method.