UV Peak Research Articles

Structural, morphological, and optical properties of tin(IV) oxide nanoparticles synthesized using Camellia sinensis extract: a green approach

Tin oxide (SnO2) nanoparticles were cost-effectively synthesized using nontoxic chemicals and green tea (Camellia sinensis) extract via a green synthesis method. The structural properties of the obtained nanoparticles were studied using X-ray diffraction, which indicated that the crystallite size was less than 20 nm. The particle size and morphology of the nanoparticles were analyzed using scanning electron microscopy and transmission electron microscopy. The morphological analysis revealed agglomerated spherical nanoparticles with sizes varying from 5 to 30 nm. The optical properties of the nanoparticles’ band gap were characterized using diffuse reflectance spectroscopy. The band gap was found to decrease with increasing annealing temperature. The O vacancy defects were analyzed using photoluminescence spectroscopy. The increase in the crystallite size, decreasing band gap, and the increasing intensities of the UV and visible emission peaks indicated that the green-synthesized SnO2 may play future important roles in catalysis and optoelectronic devices.

Effect of disorder on the optical response of NiPt and Ni3Pt alloys

In this communication we present a detailed study of the effect of chemical disorder on the optical response of Ni1−xPtx (0.1⩽x⩽0.75) and Ni3(1−x)/3Ptx (0.1⩽x⩽0.3). We shall propose a formalism which will combine a Kubo-Greenwood approach with a DFT based tight-binding linear muffin-tin orbitals (TB-LMTO) basis and augmented space recursion (ASR) technique to explicitly incorporate the effect of disorder. We show that chemical disorder has a large impact on optical response of Ni-Pt systems. In ordered Ni-Pt alloys, the optical conductivity peaks are sharp. But as we switch on chemical disorder, the UV peak becomes broadened and its position as a function of composition and disorder carries the signature of a phase transition from NiPt to Ni3Pt with decreasing Pt concentration. Quantitatively this agrees well with Massalski’s Ni-Pt phase diagram (Massalski, 1990). Both ordered NiPt and Ni3Pt have an optical conductivity transition at 4.12eV. But disordered NiPt has an optical conductivity transition at 3.93eV. If we decrease the Pt content, it results a chemical phase transition from NiPt to Ni3Pt and shifts the peak position by 1.67eV to the ultraviolet range at 5.6eV. There is a significant broadening of UV peak with increasing Pt content due to enhancement of 3d(Ni)-5d(Pt) bonding. Chemical disorder enhances the optical response of NiPt alloys nearly one order of magnitude. Our study also shows the fragile magnetic effect on optical response of disordered Ni1−xPtx (0.4<x<0.6) binary alloys. Our theoretical predictions agree reasonably well with both previous experimental findings as well as theoretical investigations.

New trends in ZnO nanoparticles/n-Si heterojunction photodetector preparation by pulsed laser ablation in ethanol

In this paper, ZnO nanoparticles/n-Si heterojunction photodetectors were fabricated by laser ablation of zinc oxide nanoparticles NPs in ethanol solution. The effect of laser fluence on the structural, optical and electrical properties of synthesized ZnO nanoparticles was demonstrated. The optical properties showed that the ZnO has direct energy gap ranging from 3.1 to 3.35eV depending on laser flunce. X-ray diffraction XRD results confirmed that the ZnO NPs are crystalline in nature with hexagonal wurtzite structure. Scanning electron microscope SEM investigation confirmed that synthesised ZnO particles have average size of 70–85nm and nanoparticles agglomeration was noticed. Photoluminescence measurements show exciton UV and visible peaks emission. The dependence of electrical properties of ZnO NPs/n-Si heterojunction photodetectors on laser fluence has been studied and analyzed. All the heterojunctions exhibited good rectifying nature and ideality factor was in the range of 2.4–3.7. The spectral responsivity results showed that all photodetectors have two peaks of response located at 650nm and 800nm with maximum responsivity of 0.32 and 0.63A/W, respectively without using post deposition annealing.

The effect of seed layer on optical and structural characteristics of ZnO nanorod arrays deposited by CBD method

ZnO nanorods were grown on p-type silicon by chemical bath deposition technique (CBD). ZnO nanorod arrays exhibited antireflective properties on silicon substrates. The ZnO nanorods structure, roughness characteristics of the film and phase were studied using field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) while the optical properties were investigated by photoluminescence (PL) and reflectance spectrometery. XRD pattern indicated a sharp peak from (002) planes of ZnO. FESEM images indicated that the average diameter and length of the ZnO nanorods were 61.27 nm and 1.22 µm, respectively. Photoluminescence spectra exhibited a strong UV peak due to near-band-edge (NBE) emission. ZnO layer can reduce the reflection of incident light from silicon surface, thus it can be assumed an antireflective layer on Si substrates. Low running cost, cheap materials and compatibility of industrial process make this structures attractive for industrial optoelectronic devices.

Optimization of pectinase-assisted and tri-solvent-mediated extraction and recovery of lycopene from waste tomato peels.

In the present work, optimization of pectinase-assisted and tri-solvent-mediated extraction of lycopene from waste tomato peels was carried out. The optimized parameters for enzymatic pre-treatment were 2% pectinase concentration, pH 5.5, 4-h incubation, 45°C and 150rpm. Maximum recovery of lycopene from tomato peels using optimized tri-solvent extraction was achieved at 45°C, 120-min incubation and 200rpm. The extracted lycopene was confirmed through functional and characteristic peaks in UV-Vis and FTIR spectra and with retention time in HPLC. The radical scavenging activity was 72.30±2.70 and 43.40±2.01µg ascorbic acid equivalents (AAE)/ml for 1,1-diphenyl-2-picrylhydrzyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radicals, respectively. The optimized method resulted in 7.38, 4.65 and 1.59 times enhancement in lycopene extraction and recovery in correlation with single solvent, enzyme-treated and tri-solvent extraction methods, respectively.

An effective low-temperature solution synthesis of Co-doped [0001]-oriented ZnO nanorods

We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 °C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g ∼ 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zni+) as CDs and oxygen vacancy (VO) or oxygen interstitial (Oi) as surface defects. As a result, Co was found to likely occupy the Zni+, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method.

Synthesis of ZnO nanorods by microwave-assisted chemical-bath deposition for highly sensitive self-powered UV detection application

High-quality vertically aligned zinc oxide (ZnO) nanorods were successfully grown on seeded silicon substrates p-Si(100) through microwave-assisted chemical bath deposition. Structural and morphological analyses revealed hexagonal wurtzite nanorods perpendicular to the substrate along the c-axis in the direction of the (002) plane. Optical measurements showed a high-intensity UV peak with a low broad visible peak. UV emission was compared with the visible emission having an IUV/Ivis ratio of 53. A metal–semiconductor–metal-based UV detector was then fabricated by depositing two metal contacts onto the ZnO nanorod surfaces. Current–voltage measurements revealed a highly sensitive device with a self-powered characteristic. At zero applied bias, the fabricated device showed a significant difference between the UV current and dark current. The device further showed a sensitivity of 304×104 to low-power (1.5mW/cm2) 365nm light pulses without an external bias. Photoresponse measurements demonstrated the highly reproducible characteristics of the fabricated UV detector with rapid response and baseline recovery times of 10ms. This work introduced a simple, low-cost method of fabricating rapid-response, highly photosensitive UV detectors with zero power consumption.

Preparation and characterization of electrodeposited SnS:In thin films: Effect of In dopant

SnS:In thin films were grown on fluorine doped tin oxide (FTO) substrate by cathodic electrodeposition technique. The solution was containing 2mM SnCl2 and 16mM Na2S2O3 and different amounts of 1mM InCl3 as In-dopant. The pH, bath temperature, deposition time, and deposition potential (E) were fixed at 2.1, 60°C, 30min, and −1V, respectively. The XRD results showed that the synthesized films were polycrystalline orthorhombic SnS. The XPS results demonstrated that the films were composed of Sn, S and In. According to the FESEM images, an increase in In-dopant concentration leads to a change in morphology from grain-like to sheet-like having a nanoscale thickness of 20–80nm and fiber-like. The PL spectra of undoped SnS exhibited four emission peaks including a UV peak, two blue emission peaks, and an IR emission peak. According to the UV–Vis spectra, the direct band gap of SnS:In thin films was estimated to be 1.40–1.66eV.

Effect of annealing on the structural, optical, electrical and photocatalytic activity of ZrO2–TiO2 nanocomposite thin films prepared by sol–gel dip coating technique

ZrO2–TiO2 nanocomposite thin films were deposited onto quartz substrate by sol–gel dip coating technique. The structural, morphological, optical, electrical and photocatalytic properties of the films were studied for different annealing temperatures (500, 800 and 1200 °C). X-ray diffraction pattern of films annealed at 500 °C showed amorphous nature. Increase in crystallinity was observed in the films annealed at higher temperature. Films annealed at higher temperature showed the formation of orthorhombic ZrTiO4 phase. Field emission scanning electron microscopy (FESEM) revealed crack free surface and surface roughness was found to increase with increase in annealing temperature. Energy dispersive X-ray analysis confirmed the presence of Zr, Ti and O in these films. Band gap of the films decreased from 3.93 to 3.50 eV with increase in annealing temperature. Photoluminescence spectra of the films exhibited emission peaks in both UV and visible region of the electromagnetic spectra. The conductivity of the films increased with increase in annealing temperature. Photocatalytic activity of these films evaluated by monitoring the degradation of methylene blue solution increased with increase in annealing temperature.

Low-temperature synthesis of hexagonal barium ferrite (BaFe12O19) nanoparticles by annealing at 450 °C followed by quenching

Citrate precursor method has been used to obtain nanosized particles of barium hexaferrite at low temperatures. Samples were annealed at 450 °C for 3 and 5 h. Quenching of the third sample was done by taking the crucible out from the muffle furnace after annealing it for 5 h and putting it abruptly into an ice bath. The saturation magnetization has been found to be 4.36 and 0.04 emu g−1 for the samples obtained upon annealing at 450 °C for 3 and 5 h, respectively, while that of the quenched sample has been found to be 4.61 emu g−1. In case of the sample obtained after 5-h annealing, the squareness value was found to be maximum indicating significance in memory and switching applications. For the quenched and the 3-h annealing products, the magnetic data values are similar. Creation of spin disorders on the surface upon prolonged annealing, due to disappearance of oxygen ions and subsequent breakage of superexchange interactions between cations, has been undone upon quenching. The XRD and TEM data indicate that the particle size (9–17 nm) gets lower in case of the quenched samples. Photoluminescence study of the quenched sample furnished prominent peaks in UV, visible and near-IR regions under 200-nm excitation. The TG–DSC data were analysed for the kinetic parameters, activation energy (E), pre-exponential factor (A) using the Kissinger isoconversion and the Ozawa–Flynn–Wall methods for the first-step decomposition of the quenched sample.

A safe, efficient and environment friendly biosynthesis of silver nanoparticles using Leucaena leucocephala seed extract and its antioxidant, antimicrobial, antifungal activities and potential in sensing

Abstract One step green synthesis of silver nanoparticles (AgNPs) from silver nitrate (AgNO3) using Leucaena leucocephala seeds extract as the reducing agent at room temperature was performed. The bioreduced NPs were characterized by UV-vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with energy dispersive spectrophotometry, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) techniques. Qualitative information of major components in the seed extract was obtained through its phytochemical screening. The phytochemical data of L. leucocephala revealed the presence of terpenes, flavonoids, coumarins and sterols. The reaction was optimized for AgNO3, extract concentration and time duration for the reaction. The obtained NPs showed a characteristic UV peak of AgNPs at 420 nm. TEM and SEM images showed the spherical shaped NPs over which the extract coating was very prominent. The binding of L. leucocephala seeds extract onto NPs was tested using FTIR and TGA. The antifungal activity of the as-synthesized NPs against two fungal species, namely Phlebiopsis gigantea and Echinodontium taxodii, was studied. The antimicrobial effect of the as-synthesized NPs was ascertained against Escherichia coli and Staphylococcus aureus. The antioxidant potential of the AgNPs was tested with 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. Also, the sensitivity of the NPs towards Fe3+ ions was tested in aqueous media.

Fabrication, Characterization and Dielectric Studies of NBR/Hydroxyapatite Nanocomposites

Nitrile rubber (NBR) based nanocomposite consists of different concentrations of hydroxyapatite nanoparticles (HA) were prepared and characterized by FTIR, UV and X-ray diffraction studies. The surface morphology of the nanocomposites were analyzed using SEM and optical microscopy. The glass transition temperature and thermal stability of NBR and its nanocomposites were done by DSC and TGA respectively. The electrical properties such as AC conductivity, dielectric constant and dielectric loss tangent were investigated in the frequency range of 102–106 Hz at room temperature. The FTIR spectra confirmed the interfacial interaction between NBR and the HA nanoparticles. The shift in the UV peak with broadness of composite indicates the formation of nanoparticles within the macromolecular chain of NBR. XRD pattern ascertained the ordered arrangement of nanoparticles with a decrease in the amorphous nature of parent polymer. Both the glass transition temperature and the thermal stability of the nanocomposites were higher than pure NBR and the glass transition temperature improved with the increase in concentration of nanoparticles in NBR composite indicating the strong interfacial adhesion between the polymer and nanoparticles. From DSC studies, thermodynamic parameters such as enthalpy and entropy change of the composites were also evaluated. AC conductivity of the nanocomposite was much greater than NBR and the magnitude of conductivity enhanced with the addition of nanoparticles. The observed enhancement in dielectric constant and dielectric loss tangent of composite with the increase in concentration of nanoparticle was attributed to the increase in number of interfacial interaction between the polymer and the nanoparticles.

Mycodecolorization of Reactive Red HE7B dye by Achaetomium strumarium and Aspergillus flavus and shelf life determination

AbstractThe decolorization of Reactive Red HE7B dye, a sulphonated reactive azo dye, was achieved under static condition with Achaetomium strumarium (KR262716) and Aspergillus flavus (KJ880096). The growth profile of isolated organisms and physicochemical parameters from the dye was fitted into a multiple linear regression model to predict the shelf life. The dye has an estimated shelf life of 36 months. The fungi showed complete decolorization of over 95% within 15 days. While A. flavus achieved maximum decolorization at a neutral pH, maximum decolorization was achieved by A. strumarium at pH of 6. The fungi optimally decolorized the dye at a temperature of 35°C. The UV–Visible and FTIR spectrometric analyses were used to study decolorization. The decrease, shifts and disappearance of peaks in UV and FTIR spectra of treated samples indicated myco-decolorization. The formation of aromatic amine was supported by Fourier Transform Infrared spectrometry (FTIR), which revealed the disappearance of certain pea...

Synthesis of Magnesium-Doped ZnO Rods via Hydrothermal Method: A Study of the Structural and Optical Properties

Magnesium (Mg) with a concentration range of 1 to 3 at% was successfully doped in zinc oxide (ZnO) and prepared via a hydrothermal process in powder form. X-ray diffraction patterns revealed a polycrystalline nature of the prepared powders. Images taken by a scanning electron microscope showed that the synthesized powders had clear solid hexagonal rod structures. Furthermore, the solid hexagonal structures were hollow because of the Mg ions introduced into the ZnO. The photoluminescence emission of the undoped and Mg-doped ZnO showed an enhancement of the ultraviolet emission with the Mg concentrations. Furthermore, the Gaussian fitting reveals that the UV band emission is consist of two emissions. The first peak was at 3.36 eV for the undoped ZnO that shifts to 3.4 eV, 3.43 eV for the 1 at% Mg and 2 at% Mg concentration, respectively. Thereafter the UV peak position reduced to 3.39 eV for the 3 at% Mg ions concentration. The results were studied, and the correlation of the results was attributed to the doping process.

Photoluminescence on cerium-doped ZnO nanorods produced under sequential atomic layer deposition–hydrothermal processes

Doped and undoped ZnO nanorod arrays were produced combining atomic layer deposition and hydrothermal processes. First, a ZnO layer with preferential orientation normal to the c-axis was grown on the substrate by means of the decomposition of diethylzinc; subsequently, the nanorod arrays were produced through solvothermal process using a solution of Zn(NO3)2 as precursor. Doped ZnO nanorods were produced using Ce(C2H3O2)3·H2O as dopant agent precursor. Undoped and Ce-doped ZnO nanorod arrays showed high-intensity photoluminescence. The doping concentration of x = 0.04 (Zn1−xCexO) displayed the highest photoluminescence. Undoped ZnO showed an intense UV peak centered at 382 nm with a narrow full wide half maximum of 33 nm. Ce-doped ZnO PL spectra contain three bands, one signal in the UV region centered at 382 nm, other centered at 467 nm in the near-green region and other one emission centered at 560 nm. The results herein exposed demonstrate the capability to produce high-quality ZnO and Zn1−xCexO films.

The unusual eyes of Xenos peckii (Strepsiptera: Xenidae) have green- and UV--sensitive photoreceptors.

The highly specialized evolution of Strepsiptera has produced one of the most unusual eyes among mature insects, perhaps in line with their extremely complex and challenging life cycle. This relatively rare insect order is one of the few for which it has been unclear what spectral classes of photoreceptors any of its members may possess, an even more apt question given the nocturnal evolution of the group. To address this question, we performed electroretinograms on adult male Xenos peckii: we measured spectral responses to equi-quantal monochromatic light flashes of different wavelengths, and established VlogI relationships to calculate spectral sensitivities. Based on opsin template fits, we found maximal spectral sensitivity (λmax) in the green domain at 539 nm. Application of a green light to 'bleach' green receptors revealed that a UV peak was contributed to by an independent UV opsin with a λmax of 346 nm. Transcriptomics and a phylogenetic analysis including 50 other opsin sequences further confirmed the presence of these two opsin classes. While these findings do not necessarily indicate that these unorthodox insects have color vision, they raise the possibility that UV vision plays an important role in the ability of X. peckii males to find the very cryptic strepsipteran females that are situated within their wasp hosts.

Efficient extraction and purification of flexibilane and tigliane diterpenoids from Stillingia lineata using sequential SFE-CO2 and SFC-CO2

Quite a number of methods of extraction and separation are currently used to isolate and purify secondary metabolites from complex mixtures, but "green" technologies are still far from being used routinely in public research laboratories. In recent years, supercritical fluid extraction (SFE) and chromatography (SFC) have gained increasing interest in production of high-value plant extracts for pharmaceutical, cosmetic and food industries. SFC enables fast and reliable separation of biomolecules from complex mixtures [1,2]. Supercritical carbon dioxide (SC-CO2) is an eco-friendly, chemically inert, nontoxic and noninflammable fluid. As a green material, SC-CO2 has low viscosity and high diffusivity that make it suitable as a solvent for SFE and as a mobile phase for SFC. Previous chemical investigation of Stillingia lineata ((Lam.) Müll. Arg. Euphorbiaceae) leaves led to the isolation of the rare C20-flexibilane tonantzitlolones (TZLs) (PKC activators and potent anti-tumor agents) [3] and tigliane derivatives (strong inhibitors of Chikungunya viral replication) [4 – 6]. This plant was selected to validate our green approach aiming to specifically extract, then isolate diterpenoids of interest. According to a pre-determined experimental plan, sequential SFE-CO2 was carried out by varying pressure, temperature, flow rate and step duration. For each experiment, an ethanol step gradient was performed, affording six fractions (Figure below). Identification of compounds was achieved by LC-UV-HRMS [2], then compared with standards and classified into different chemical classes (TZLs, diterpenes, chlorophylls and glycosylated flavonoids). Their relative proportions were subsequently determined by measurement of UV peak areas, allowing selecting optimal SFE conditions, and diterpene-enriched fraction for further SFC purifications. This approach not only has the benefit of using eco-friendly methodologies, but it also allows a concurrent prefractionation during the extraction step.

Photoluminescence properties of fully concentrated Terbium oxalate: A novel efficient green emitting phosphor

A novel green emitting phosphor, Terbium oxalate decahydrate, was synthesized in crystalline form employing the hydro silica gel method. The structure of the sample was confirmed by x-ray diffraction analysis. Photoluminescence excitation spectrum of the sample shows several peaks in the deep UV to Visible region, matching well with the commercially available LED sources. Emission spectrum, recorded with representative excitation wavelengths revealed efficient luminescence, particularly the green emission at 543nm. The decay time of the sample was measured to be 0.81ms. It exhibits a colour purity of 68% with chromaticity coordinates (0.31, 0.57) which is very close to that of the European Broadcasting Union illuminant green.

Fabrication and characterization of SiO2@SiC shell–core nanowire prepared by laser sintering

One-dimensional SiO2@SiC shell–core nanowire was fabricated on a SiC substrate without any catalyst using a laser sintering method. Based on a solid–liquid–vapor–solid (SLVS) in situ growth mechanism, the as-synthesized SiO2@SiC nanowires of about 60 nm diameter with a shell thickness of about 13 nm were grown. Varying the power density of laser sintering allowed the final SiC particle morphology to be controlled from grainy to whisker-like. High power density or high temperature benefited the nucleation probability of SiC whiskers. The isothermal oxidation test showed that the SiO2@SiC nanowires have good thermodynamic stability at high temperature. The photoluminescence (PL) property of SiO2@SiC nanowire was also investigated. The observed emission peaks were composed of an UV peak centered at 365 nm (3.40 eV) and a blue peak centered at 453 nm (2.74 eV). The theory behind the PL property and the growth mechanism of the SiO2@SiC nanowire were also discussed.

Temperature characterization of dielectric permittivity and AC conductivity of nano copper oxide-doped polyaniline composite

The polyaniline/copper oxide (PANI/CuO) nanocomposite was prepared by mixing solutions of polyaniline and copper oxide nanoparticles in dimethyl sulfoxide (DMSO). The synthesized polymer nanocomposites were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and UV–visible spectroscopy. The characteristic peaks in XRD and UV–visible spectra confirmed the presence of CuO in the polymer structure. SEM images indicated morphological changes in the composite matrix as compared to the pristine PANI. The DC conductivity measurements were performed using two-probe method for various temperatures. AC conductivity and dielectric response of the composites were investigated in the frequency range of [Formula: see text]–[Formula: see text][Formula: see text]Hz using LCR meter. Dielectric permittivity [Formula: see text] and dielectric loss factor [Formula: see text] were investigated. It was observed that [Formula: see text] and [Formula: see text] decrease with increase in frequency at all temperatures. At a particular frequency it is observed that both [Formula: see text] and [Formula: see text] increase with increase in temperature. It was also observed that AC conductivity increased with increase in frequency and temperature.