Short Wavelength Region Research Articles

THE INFLUENCE OF ACID PROTEIN PRECIPITANTS ON THE SPECIFICITY OF THE REACTION OF NINHYDRIN WITH AMINO ACIDS

Aim. The purpose of the work was to determine the effect of trichloroacetic (TCA) and perchloric (HClO4) acids on the result of ninhydrin reaction with various amino acids. Methods. A standard method of amino acid detection using a ninhydrin reagent was applied. Optical spectra and density of reaction products were determined spectrophotometrically. Results and conclusions. As a result, it was found that the studied acids change the spectral characteristics of the products of the ninhydrin reaction with amino acids. TCA significantly reduced the optical density of chromophores, and HClO4 also led to a significant shift of the spectra of the reaction products into the short-wavelength region. An exception was the reaction with proline, as a result of which a well-defined maximum appeared in the product spectrum: λ= 620 nm in the presence of TCA and λ=515 nm with HClO4. At the same time, in the presence of HClO4, the reaction became highly specific for proline. Conditions. The ninhydrin reaction with proline upon addition of HClO4 were analyzed in detail. As a result, a new method of highly specific determination of proline in the presence of other amino acids was proposed.

Influence of the environment on the morphology, optical and electrical characteristics of the PEDOT:PSS polymer

The paper presents the results of studying the influence of the environment on the surface structure, optical and electrical characteristics of the PEDOT:PSS film. The studies have been carried out in three different types of atmosphere under the same conditions of thermal annealing of the films. It has been established that the modification of the surface of a polymer film with ethanol and isopropanol in vacuum, in a nitrogen atmosphere, and in the air atmosphere leads to a change in the surface morphology and the optical electric transport properties of the polymer. Depending on the environment, when the PEDOT:PSS film is modified with a certain concentration of ethyl and isopropyl alcohols, the absorption spectra show a shift in the absorption maximum responsible for PEDOT to the short-wavelength region of the spectrum, as well as a decrease in the absorption peak of the part of the spectrum responsible for the absorption of the aromatic fragment PSS. It is identified that the structural features of the PEDOT:PSS surface morphology affect the electrical transport parameters of the films: Rh is the resistance of the PEDOT:PSS polymer film, Rext is the charge carrier transfer resistance at the PEDOT:PSS/electrode interface, keff is the effective charge carrier extraction rate and τeff is the effective transit time of charge carriers. The optimal technological parameters for film production have been determined, at which the electrical transport properties of PEDOT:PSS polymer film are increased.

Influence of the environment on the morphology, optical and electrical characteristics of the PEDOT:PSS polymer

The paper presents the results of studying the influence of the environment on the surface structure, optical and electrical characteristics of the PEDOT:PSS film. The studies have been carried out in three different types of atmosphere under the same conditions of thermal annealing of the films. It has been established that the modification of the surface of a polymer film with ethanol and isopropanol in vacuum, in a nitrogen atmosphere, and in the air atmosphere leads to a change in the surface morphology and the optical electric transport properties of the polymer. Depending on the environment, when the PEDOT:PSS film is modified with a certain concentration of ethyl and isopropyl alcohols, the absorption spectra show a shift in the absorption maximum responsible for PEDOT to the short-wavelength region of the spectrum, as well as a decrease in the absorption peak of the part of the spectrum responsible for the absorption of the aromatic fragment PSS. It is identified that the structural features of the PEDOT:PSS surface morphology affect the electrical transport parameters of the films: Rh is the resistance of the PEDOT:PSS polymer film, Rext is the charge carrier transfer resistance at the PEDOT:PSS/electrode interface, keff is the effective charge carrier extraction rate and τeff is the effective transit time of charge carriers. The optimal technological parameters for film production have been determined, at which the electrical transport properties of PEDOT:PSS polymer films are increased.

ZnS, CdSe and ZnSe magneto-optical and thermo-optical characteristics

In the presented work, the prospects for using pure ZnS and CdSe semiconductors for the development of Faraday isolators are investigated. Both materials have advantages over conventional magnetoactive materials. Their use can make it possible to expand the spectral range, in which isolators for high-power laser radiation can be implemented, both in the long-wavelength and short-wavelength regions. Measurements of the Verdet constant of crystals and the dependence of thermally induced depolarization caused by stress-induced birefringence on laser power were carried out. Based on the obtained experimental data, the parameters of the magneto-optical figure of merit were determined. The studied samples showed promising results, while the potential for increasing the magneto-optical figure of merit by optimizing the parameters of the production process is assessed as high. This possibility is illustrated by the example of ZnSe crystal samples obtained in various technological processes.

Bipolar dual-broadband photodetectors based on perovskite heterojunctions

The development of efficient photodetectors for color recognition is of great importance for many applications. In this paper, we report a novel bipolar dual-broadband photodetector equipped with a perovskite heterojunction, with bidirectional broadband responses in the short-wavelength and long-wavelength regions at zero bias voltage, enabled by a charge separation reversion mechanism. The unique aerosol–liquid–solid technique allowed the perovskite heterojunction to be fabricated by successively depositing wide-bandgap perovskite (WBP) and narrow-bandgap perovskite (NBP) layers directly on the transparent substrate. For photodetectors based on the perovskite heterojunctions, the short-wavelength photons were depleted by the bottom WBP layer and generated negative responses, while the long-wavelength photons were absorbed by the top NBP layer and generated positive responses. Moreover, the demarcation wavelength between the bipolar responses and the cut-off wavelength can be easily tuned by adjusting the bandgaps (or compositions) of the bottom and top perovskite layers.

Importance of optical homogeneity for high-quality transparent ceramics

Two types of transparent Y2O3 ceramics without including large scattering sources such as residual pores, one with very high optical homogeneity (type A) and another one with slightly insufficient optical homogeneity (type B), are purposely prepared, and their optical properties are investigated and compared qualitatively and quantitatively. Type A ceramic exhibits transmittance characteristics with very low internal loss in the visible to infrared wavelength region, while type B ceramic is inferior in various optical performances especially in the short (visible) wavelength region. In type B ceramic, birefringence occurs due to optical inhomogeneity in the visible region, resulting in a decrease in the extinction ratio. Non-uniform refractive index distribution is also observed in the Schlieren image of type B ceramic, hence the laser beam quality through that material is degraded. This study proved the importance of optical homogeneity of transparent ceramics and clarified the problems in actual applications.

Generation of 8–20 μm Mid-Infrared Ultrashort Femtosecond Laser Pulses via Difference Frequency Generation

Mid-infrared (MIR) ultrashort laser pulses have a wide range of applications in the fields of environmental monitoring, laser medicine, food quality control, strong-field physics, attosecond science, and some other aspects. Recent years have seen great developments in MIR laser technologies. Traditional solid-state and fiber lasers focus on the research of the short-wavelength MIR region. However, due to the limitation of the gain medium, they still cannot cover the long-wavelength region from 8 to 20 µm. This paper summarizes the developments of 8–20 μm MIR ultrafast laser generation via difference frequency generation (DFG) and reviews related theoretical models. Finally, the feasibility of MIR power scaling by nonlinear-amplification DFG and methods for measuring the power of DFG-based MIR are analyzed from the author’s perspective.

Interdisk spacing effect on resonant properties of Ge disk lattices on Si substrates

The light reflection properties of Ge disk lattices on Si substrates are studied as a function of the disk height and the gap width between disks. The interdisk spacing effect is observed even at such large gap widths as 500 nm. The gap width decrease leads to the appearance of the reflection minimum in the short wavelength region relative to one originated from the magnetic and electric dipole resonances in individual Ge disks, thereby essentially widening the antireflection properties. This minimum becomes significantly deeper at small gap widths. The observed behavior is associated with the features of the resonant fields around closely spaced disks according to numerical simulation data. The result shows the importance of using structures with geometrical parameters providing the short-wavelength minimum. This can essentially enhance their other resonant properties, which are widely used for applications, in particular, based on collective lattice resonances.

Stimulus responsive luminescence and application of rotor type 1,1′-([2,2′-bithiophene]-3,3′-diyl)bis(ethan-1-one) and 3′-acetyl-[2,2′-bithiophene]-3-carbaldehyde as molecular rotors

Two dithiophene aldehyde/ketone derivatives are designed as luminescence molecular rotors, i.e., 1,1′-([2,2′-bithiophene]-3,3′-diyl)bis(ethan-1-one) (BTBE) and 3′-acetyl-[2,2′-bithiophene]-3-carbaldehyde (BTAC). Their absorption and luminescence properties, as well as the stimulus responsive luminescence characteristics of water spikes are studied in detail. In order to further explore relationship of luminescence and molecular structure, three reference compounds are also synthesized, named 1-(2-methylthiophen-3-yl)ethanone (MTE), 2-methylthiophene-3-carbaldehyde (MTC) and 4H-cyclohepta[1,2-b:7,6-b’]dithiophen-4-one (CDTO). BTBE and BTAC have two obvious absorption bands in the short wavelength region with peak wavelengths of about 212 nm and 260 nm, respectively, while there is a weak trailing type absorption band in the range of about 300–400 nm. Their fluorescence spectra show two luminescence bands in the range of 280–350 nm and 400–600 nm, respectively, and the latter is stronger. Compared with the absorption and luminescence spectra of the reference compounds, it is determined that two absorption bands of BTBE and BTAC in shorter wavelength region are derived from the single thiophene ring carbonyl planar unit, while the absorption band in longer region are derived from the integrated structure of dithiophene carbonyl. The fluorescence bands with peaks of about 300 nm and 470 nm originate respectively from the localized F-C vertical excited states (LE), i.e., the excited state from single planar thienyl-carbonyl unit, and integrated excited state (IE), i.e., the excited state from integrated di-thienyl-carbonyl rings linked covalently with less dihedral angle and greater degree of conjugation at excited state. The crystal structure data show that two thiophene rings possess larger dihedral angles in crystal states, 86.9° for BTBE and 60.8° for BTAC, respectively. However, theoretical calculation results prove the conformational stabilization energy changes little, less than 1.5 kcal/mol, as dihedral angle changes from 50° to 100°. Hydrogen bonding is sufficient to overcome the energy required for this conformational change. Therefore, both BTBE and BTAC can produce water stimulation response luminescence behavior. This stimulating response behavior of BTBE and BTAC can be applied to the preparation of water writable film materials.

Numerical simulation of quantum dots as a buffer layer in CIGS solar cells: a comparative study

Quantum bandgap buffer layers can improve sunlight absorption in the short wavelength region, hence improving the performance of CIGS solar cells. In this study, we use numerical modelling to determine the impact of various buffer layers' electrical characteristics on the performance of CIGS thin film photovoltaic devices, particularly, carrier concentration and the quantum effect. As well Ag2S buffer layer has been experimentally examined to fulfilment its effect in term of bulk and quantum bandgap. Experimental results depicted that, Ag2S QDs has polycrystalline nature of films, with smooth surface roughness, and average diameter 4 nm. Meanwhile, a simulation revealed that the Fermi level of the (n-buffer layer) material shifts closer to the conduction band with an increase in carrier concentration. The findings indicate that, a buffer layer with a wider bandgap and carrier concentration is an essential demand for achieving a device with a higher conversion efficiency and a broader bandgap-CBO window. It was attributed to beneficial synergistic effects of high carrier concentration and narrower depletion region, which enable carriers to overcome high CBO barrier. Most importantly, modelling results indicate that the optic-electrical characteristics of the buffer layer are critical in determining the progress of a CIGS solar cell.

Enhancement of Birefringence in Borophosphate Pushing Phase-Matching into the Short-Wavelength Region.

Borophosphates are very known for the short ultraviolet (UV) cutoff edge and have become the promising UV and deep-UV functional crystals candidates; however, tetrahedral [PO4] and [BO4] groups own weak anisotropy of polarizability and are not conducive to large birefringence, which hinders their application in the short-wavelength region. Improving their birefringence without compromising the band gap is the main research objective. By introducing the excellent birefringent functional groups, such as [B2O5], [BO2]∞ chain, [B2Ox(OH)5-x], and so forth into borophosphates, seven borophosphates with improved birefringence were successfully synthesized (Δn > 0.05@532 nm). Remarkably, among them, the centimeter-sized crystal of Rb3B8PO16 with a short deep-UV cutoff edge (175 nm) and large birefringence (Δn(exp.) ∼ 0.072@589.3 nm) exhibits the shortest phase-matching wavelength (222 nm), which makes Rb3B8PO16 a promising UV NLO crystal, while KB6PO10(OH)4 with deep-UV cutoff edge features the largest birefringence (Δn(exp.) ∼ 0.103@546 nm) in the reported borophosphate system, making KB6PO10(OH)4 a promising deep-UV birefringent crystal. This study not only provides feasible strategies for increasing the birefringence of borophosphates but also pushes phase-matching into the short-wavelength region.

Variations in the Physical Properties of RF-Sputtered CdS Thin Films Observed at Substrate Temperatures Ranging from 25 °C to 500 °C.

CdS films with a wide range of substrate temperatures as deposition parameters were fabricated on Corning Eagle 2000 glass substrates using RF magnetron sputtering. The crystallographic structure, microscopic surface texture, and stoichiometric and optical properties of each CdS film deposited at various substrate temperatures were observed to be highly temperature-dependent. The grown CdS thin films revealed a polycrystalline structure in which a cubic phase was mixed based on a hexagonal wurtzite phase. The relative intensity of the H(002)/C(111) peak, which represents the direction of the preferential growth plane, enhanced as the temperatures climbed from 25 °C to 350 °C. On the contrary, the intensity of the main growth peak at the higher temperatures of 450 °C and 500 °C was significantly reduced and exhibited amorphous-like behavior. The sharp absorption edge revealed in the transmission spectrum shifted from the long wavelength to the short wavelength region with the rise in the substrate temperature. The bandgap showed a tendency to widen from 2.38 eV to 2.97 eV when the temperatures increased from 25 °C to 350 °C. The CdS films grown at the temperatures of 450 °C and 500 °C exhibited glass-like transmittance with almost no interference fringes of light, which resulted in wide bandgap values of 3.09 eV and 4.19 eV, respectively.

Amplification of laser radiation at the edge of the KrF (B–X) spectral line

We report the results of experimental and numerical studies of the KrF electric discharge amplifier operating on a mixture of He – Kr – F2 gases. The possibility of expanding the short-wavelength spectral region of the induced radiation tuning at the B – X transition of the KrF molecule by removing the inverse population from the upper vibrational states of the electronic B level is shown. It is demonstrated that at the boundary of the active medium gain contour, the measured gain at a wavelength of 246.8 nm is 0.053 cm−1. Using the developed 1D model of the KrF electric discharge amplifier, it is shown that when the active medium is excited by a pump pulse with a specific peak power of ∼10 MW cm−3, the gain in this spectral region is due to a longer relaxation time of the population of excimer molecules from the upper vibrational levels compared with the characteristic time of their production.

Variation of the sign of nonlinear refraction of carbon disulfide in the short-wavelength region

We report the spectral dependence of the nonlinear refractive index (γ) of carbon disulfide (CS2) in the range of 400–1100 nm in the case of the femtosecond laser pulses. The positive sign of γ dominated in the region between 600 and 1100 nm. At a shorter wavelength (500 nm), we observed the intensity-dependent competition between the fifth-order related self-defocusing and third-order related self-focusing. Further decrease of the wavelength of the probe pulses (400 nm) resulted in domination of the negative nonlinear refraction. The fifth-order nonlinear refractive index of CS2 at λ = 400 nm (η = −4×10−22 cm4 W−2) is determined.

Broadband Enhancement of Anti-reflectivity for a High Angle of Incidence Using Nanocone Geometry.

The broadband antireflective (AR) effect for wide incident angles has a significant effect on the photoconversion efficiency of photovoltaics and visibility of large-format display panels. The fabrication of surface nanostructures has continued to attract research interest as an effective way to provide such optical performance. However, the effects of different nanostructure geometries are not fully understood, especially for wide-angle AR effects. In this work, we conduct a systematic analysis of the effect of periodic nanostructures such as nanocones (NCs) and inverted nanocones (INCs) on anti-reflectivity at high angles of incidence (AOIs) in terms of light scattering, guided-mode resonance (GMR), and internal reflections. NCs provide good coupling of light scattering and GMR because of their protruding geometry; hence, reduced reflectance can be obtained in the short wavelength region. Further, NCs exhibit relatively weaker GMR intensities and internal reflections, resulting in low reflectance in the long wavelength region. Therefore, NCs offer a superior broadband AR effect for high AOIs compared with INCs. Based on this analysis, we demonstrate an extremely low average reflectance (5.4%) compared to that of the bare substrate (34.7%) for the entire visible range at an AOI of 75° by fabricating NCs on both sides of the substrate.

Noncentrosymmetric Rare-Earth Borate Fluoride La2B5O9F3: A New Ultraviolet Nonlinear Optical Crystal with Enhanced Linear and Nonlinear Performance.

In crystal engineering, it is an effective and controllable approach to modify the electronic band structure and optimize crystal performances using rational chemical cosubstitution in a classic structure model. Herein, the noncentrosymmetric (NCS) rare-earth borate fluoride La2B5O9F3 was designed and synthesized successfully based on the extraordinarily stable M2B5O9X (M = Ca, Sr, Ba, Sn, Pb, and Eu; X = Cl, Br, and I) template. Moreover, all 70 rare-earth borate halides were discussed, and the ratio of crystallization in NCS group is only 17.1%, much lower than 34.9% in all anhydrous borates. Benefiting from the substitution of [MOX] by [LaOF] polyhedra with improved hyperpolarizability and anisotropy of polarizability, compared with the M2B5O9X family, La2B5O9F3 with optimized band structure exhibits the suitable SHG response (1.2 × KH2PO4 (KDP) @ 1064 nm), large band gap (6.58 eV), and moderate birefringence, which well achieves the optimal balance among the three critical parameters mentioned above for nonlinear optical (NLO) applications in the short-wavelength region. This work expands the research field of NLO materials to rare-earth borate fluorides and can lead to a better understanding of the role of rare-earth metal cations.

Structural, optical and photoelectric properties of Tb doped ZnO thin films for device applications

In this work we have investigated the effect of thermal annealing of thin ZnO:Tb3+ films obtained by the combined method of electrochemical deposition of Tb ions onto silicon substrates and subsequent reactive magnetron sputtering of a zinc target on the substrates on the structural properties, optical and photoelectric properties. ZnO:Tb3+ films with annealing temperature up to 700 °C are close-packed structures without porosity, with an almost smooth surface and dense packing of crystallites. The crystallite size and film thickness increase insignificantly with increasing annealing temperature. The films under investigation exhibit strong green luminescence with three bands in the spectral region of ∼1.9–2.6 eV, caused by intracenter 4f transitions on Tb3+ ions without changing the redistribution in the relative intensity of three bands with an increase in the annealing temperature. The study of the photoelectric properties showed that with an increase in the bias voltage, the maximum of the spectral sensitivity in absolute value increases and shifts to the short-wavelength region, while with an increase in the annealing temperature, the photosensitivity decreases, and upon annealing at 1100 °C it is practically absent.

Identification of Stingless Bee Honey Adulteration Using Visible-Near Infrared Spectroscopy Combined with Aquaphotomics.

Honey is a natural product that is considered globally one of the most widely important foods. Various studies on authenticity detection of honey have been fulfilled using visible and near-infrared (Vis-NIR) spectroscopy techniques. However, there are limited studies on stingless bee honey (SBH) despite the increase of market demand for this food product. The objective of this work was to present the potential of Vis-NIR absorbance spectroscopy for profiling, classifying, and quantifying the adulterated SBH. The SBH sample was mixed with various percentages (10–90%) of adulterants, including distilled water, apple cider vinegar, and high fructose syrup. The results showed that the region at 400–1100 nm that is related to the color and water properties of the samples was effective to discriminate and quantify the adulterated SBH. By applying the principal component analysis (PCA) on adulterants and honey samples, the PCA score plot revealed the classification of the adulterants and adulterated SBHs. A partial least squares regression (PLSR) model was developed to quantify the contamination level in the SBH samples. The general PLSR model with the highest coefficient of determination and lowest root means square error of cross-validation ( and ) was acquired. The aquaphotomics analysis of adulteration in SBH with the three adulterants utilizing the short-wavelength NIR region (800–1100 nm) was presented. The structural changes of SBH due to adulteration were described in terms of the changes in the water molecular matrix, and the aquagrams were used to visualize the results. It was revealed that the integration of NIR spectroscopy with aquaphotomics could be used to detect the water molecular structures in the adulterated SBH.

Is Ge an Excellent Material for Mid-IR Kerr Frequency Combs Around 3-μm Wavelengths?

Mid-infrared (Mid-IR) Kerr frequency combs, which emit board, discrete, and evenly spaced laser frequencies in the spectral region of 2–20 μm, are expected to bring us tremendous applications from molecular spectroscopy to astronomy science. To develop mid-IR Kerr frequency combs, Ge has attracted significant attention due to its unique merits of a wide transparency window (2–14 μm), high refractive index (∼4), giant third-order nonlinear refractive index (∼10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−16</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /W), and fully CMOS-compatible device fabrication. However, it is still debatable whether Ge is an excellent material for developing Kerr frequency combs in the short-wavelength mid-IR region due to the harmful multiphoton and free-carrier absorption effects. Here, we seek to provide physical insights into the feasibility of developing mid-infrared Ge-based Kerr frequency combs around 3-μm wavelengths. Our method is based on a comprehensive model developing from a modified Lugiato-Lefever equation via taking into account high-order dispersion, multiphoton absorption, free-carrier absorption, free-carrier dispersion, and thermal-optical phase shift effect. The results show that, only with the pump wavelength of above 3.5 μm, a frequency comb could be generated by adjusting the carrier lifetime and pump power appropriately. The study is expected to provide useful guidance for developing mid-IR Kerr frequency combs by using the CMOS technology.

Synthesis of PVA-Fe2O3-TiO2 hybrid structure for biomedical application

This work investigates the structure, morphology, and optical properties of TiO2 nanoparticles embedded in a Fe2O3–PVA composite matrix. The samples were examined using a variety of techniques, including field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), absorption and transmission spectra, and Fourier transformation infrared (FTIR). Crystallography information revealed the presence of TiO2 doesn’t effect in the crystal structure of PVA-Fe2O3. The manufactured composites demonstration strong absorption in the range of 440–570 nm. It is important that the highest absorption of these composites gradually shifted to the shorter wavelength region with presence of TiO2. PVA-Fe2O3 is highly transparent with transmittance of around 85 % in range 600-800 nm. After addition of 2.5 % by weight of TiO2 nanoparticles, the transmittance of nanocomposite drops to 75% in the same range of wavelength . Further addition of nanoparticles reduced the percentage transmittance to 68%. The results specify that as the TiO2 ratio increases, the band gap be wider.