ZnS nanosheets: Egg albumin and microwave-assisted synthesis and optical properties

ZnS nanosheets were prepared via egg albumin and microwave-assisted method. The phases, crystalline lattice structures, morphologies, chemical and optical properties were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscope(FE-SEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy and fluorescence(FL) spectrometer and growth mechanism of ZnS nanosheets was investigated. The results showed that all samples were pure cubic zinc blende with polycrystalline structure. The width of ZnS nanosheets with a rectangular nanostructure was in the range of 450–750 nm. The chemical interaction existed between egg albumin molecules and ZnS nanoparticles via the amide/carboxylate group. The band gap value calculated was 3.72 eV. The band at around 440 nm was attributed to the sulfur vacancies of the ZnS nanosheets. With increasing volumes of egg albumin, the photoluminescence (PL) intensity of ZnS samples firstly increased and then decreased, attributed to concentration quenching.     

Research on successive preparation of nano-FeNi alloy and its ethanol sol by pulsed laser ablation

Since Ogale et al.[1,2] firstly prepared metastable matter by pulsed laser ablation at the solid target sub-merged in liquid, there has been a great interest in it. Tokura et al.[3] prepared carbon films in the water by pulsed laser ablation. Zheng et al.[4—6] prepared nano and cluster matters with different shapes through pulsed laser ablation at interface of liquid and solid target. Yang et al.[7,8] prepared cube nano-nitride boron crystalloid and nano-diamond crystalloid with the same meth…     

Preparation of cellulose-based fluorescent materials using Zinc sulphide quantum dot-decorated graphene by a one-step hydrothermal method

Cellulose-based fluorescent materials using Zinc sulphide (ZnS) quantum dot-decorated graphene were prepared by a one-step hydrothermal method. X-ray photoelectron spectroscopy analysis identified the chemical states of Zn, S, C, O, and N in the composite paper. Transmission electron microscopy showed that the graphite oxide was reduced to graphene sheets, and ZnS nanoparticles (<10 nm) were deposited on the surface of these sheets. Scanning electron microscopy indicated that graphene sheets were attached to the surface of paper fibers, and the paper structure and morphology of the fibers were not observably damaged during the hydrothermal reaction. The cellulose-based composite had strong ultraviolet absorption in the range of 200–340 nm, and its main absorption peak was at approximately 296 nm. The band edge emission of photoluminescence spectrum of the composite occurred at 466 nm with an excitation wavelength of 320 nm. The laser scanning confocal microscope image of the composite exhibited an intense blue fluorescence under UV light at 405 nm.     

An improved method for chemical bath deposition of ZnS thin films

ZnS thin films were prepared by an improved chemical bath deposition method, which the substrates were preheated before being mounted in the reaction solution. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) reveals that thin film ZnS has a cubic structure and the typical composition ratio of Zn/S is 52:48. Scanning electron microscopy (SEM) characterization shows that the surface of the sample is compact and uniform. The transmission spectrum indicates a good transmission characteristic with an average transmittance of 82.2% in the spectra range from 350 nm to 800 nm and the optical band gap is about 3.76 eV.     

Photocatalytic Activity of LaSr2AlO5:Eu Ceramic Powders

The photocatalytic activity, of undoped and Europium‐doped LaSr₂AlO₅ powders, has been investigated by degrading methylene blue dye in water solutions. Those powders were fabricated by a combustion method and an annealing treatment in air. All samples showed a tetragonal single phase according to by X‐ray diffraction measurements (XRD). Scanning electron microscopy (SEM) revealed irregular semi‐oval grains with sizes in the range of 3.5–4.27 μm. Photoluminescence spectrum showed sharp emission peaks at 588 nm and at 617 nm which are associated with ⁷F₁,⁷F₂→ ⁵D₀ Eu³⁺ ion forbidden transitions, respectively, under UV light excitation of 322 nm. The methylene blue (MB) degradation under UV light (254 nm) was studied by monitoring changes in the absorbance peak of MB at 665 nm. Finally, LaSr₂AlO₅:Eu powders were used three times and the efficiency for the degradation of MB decreased from 100 to 61% after the third cycle of use.     

Phase transformation and optical properties of Cu-doped ZnS nanorods

ZnS nanorods doped with 0-15 mol% of Cu have been prepared by simple solvothermal process. With gradual increase in the Cu concentration, phase transformation of the doped ZnS nanorods from wurtzite to cubic was observed. Twins and stacking faults were developed due to atomic rearrangement in the heavily doped ZnS nanorods during phase transformation. UV-vis-NIR absorbance spectroscopy ruled out the presence of any impure Cu-S phase. The doped ZnS nanorods showed luminescence over a wide range from UV to near IR with peaks at 370, 492-498, 565 and 730 nm. The UV region peak is due to the near-band-edge transition, whereas, the green peak can be related to emission from elementary sulfur species on the surfaces of the nanorods. The orange emission at 565 nm may be linked to the recombination of electrons at deep defect levels and the Cu(t₂) states present near the valence band of ZnS. The near IR emission possibly originated from transitions due to deep-level defects.     

Microwave synthesis and characterization of europium complexes with cinnamic acid and phenanthroline

We report here the synthesis and characterization of a host of Eu(Phen)L₃ with cinnamic acid (C₆H₅CH = CHCOOH, HL) and phenanthroline (Phen), and employing microwave radiation, where the microwave radiation is used just for the uniform heating of the reaction mixture. Its IR absorption spectra, scanning electron microscopy (SEM), and fluorescence spectra were studied. The results show that the particles of Eu(Phen)L₃ phosphors are basically spherical in shape, with good dispersing. The mean particle size is 1–2 μm. The excitation spectrum is a broad band and the main peak is at 320.0 nm. Moreover, excitation peak at 396.0 nm was found in the excitation spectrum. The emission spectrum shows that Eu(Phen)L₃ has narrow emission peaks. The emission peaks are ascribed to Eu³⁺ ions transition from ⁵ D _J (J = 0) to ⁷ F _J (J = 1, 2, 4). However, the strongest main emission peak locates at 614.0 nm, which corresponds to the electric dipole transition of Eu³⁺(⁵ D ₀ → ⁷ F ₂) The article is published in the original.     

Photoinduced electron transfer and interfacial photocatalysis behaviour of ZnS/CdS binary co-colloid system

The interfacial photoinduced electron transfer and related secondary photochemical behaviour in the system of ZnS/CdS co-colloid superfine particles were studied by means of ESR and fluorescence spectroscopy techniques. The photoinduced charge-separation and the radical intermediates produced in the secondary redox reactions initiated via charge separation, as well as the mechanism of reaction processes, were investigated in detail through simultaneous excitation of two colloid components or only one of them. Research results indicated that, as E_(g(ZnS))>E_λ>E_(g(CdS)), only CdS in co-colloid system might be excited. The transfer process of electron from the conduction band of CdS to the conduction band of ZnS is forbidden, and under the excitation wavelength range used, the electron transfer of cocolloid system was impossible, thus the photo redox reactions of the substrate in co-colloid system had no obvious difference from those reactions happening in single colloid system. While the excitation wav     

Optical properties of sol-gel synthesized calcium doped ZnO nanostructures

Optical properties of Ca doped ZnO nanoparticles prepared at room temperature through wet chemical method have been investigated. X-ray diffraction studies show that particles are crystalline in nature and doping did not induce impurity phases. Optical absorption measurements show an absorption peak at ∼372 nm which is due to excitonic absorption of the ZnO. Photoluminescence studies reveal a broad emission at an excitation wavelength of 335 nm and the bands are attributed to near band edge emission, oxygen vacancies, surface dangling bonds and zinc interstitials. Incorporating Ca²⁺ induces reduction in near band edge emission and there is an enhancement in the oxygen vacancy peaks which are attributed to the shape changes in the nanoparticles.     

Preparation and characterization of ZnS nanoparticles deposited on montmorillonite

ZnS nanoparticles were prepared and deposited on montmorillonite (MMT) in the presence of cetyltrimethylammonium (CTA). UV spectrometry and transmission electron microscopy (TEM) proved the formation of nanoparticles with diameters ranging from 3 nm to 5 nm. Selected-area electron diffraction (SAED) patterns revealed the presence of romboedric ZnS. The band gap energy of nanosize ZnS was estimated at 3.89 ± 0.03 eV. Photoluminescence spectra exhibited a strong emission band between 300 nm and 600 nm explained by the vacant ZnS nanostructure. The prepared ZnS-montmorillonite nanocomposite (ZnS-MMT) was used for the photocatalytic reduction of CO(2) providing a considerably high efficiency that exceeded 5-6-fold the results of commercial TiO(2) Degussa P25. The main reaction products were hydrogen and methane. Methanol and carbon oxide were also observed in about 7-fold lower amounts. The stability of ZnS against oxidation was confirmed by the determination of sulphate using capillary isotachophoresis.     

Different level of fluorescence in Raman spectra of montmorillonites

The paper presents the study of selected montmorillonite standards by Raman spectroscopy and microscopy supported by elemental analysis, X-ray powder diffraction analysis and thermal analysis. Dispersive Raman spectroscopy with excitation lasers of 532 nm and 780 nm, dispersive Raman microscopy with excitation laser of 532 nm and 100× magnifying lens, and Fourier Transform-Raman spectroscopy with excitation laser of 1064 nm were used for the analysis of four montmorillonites (Kunipia-F, SWy-2, STx-1b and SAz-2). These mineral standards differed mainly in the type of interlayer cation and substitution of octahedral aluminium by magnesium or iron. A comparison of measured Raman spectra of montmorillonite with regard to their level of fluorescence and the presence of characteristic spectral bands was carried out. Almost all measured spectra of montmorillonites were significantly affected by fluorescence and only one sample was influenced by fluorescence slightly or not at all. In the spectra of tested montmorillonites, several characteristic Raman bands were found. The most intensive band at 96 cm⁻¹ belongs to deformation vibrations of interlayer cations. The band at 200 cm⁻¹ corresponds to deformation vibrations of the AlO₆ octahedron and at 710 cm⁻¹ can be assigned to deformation vibrations of the SiO₄ tetrahedron. The band at 3620 cm⁻¹ corresponds to the stretching vibration of structural OH groups in montmorillonites.     

Photoluminescence properties of SnO2 nanowhiskers grown by thermal evaporation

SnO₂ nanowhiskers were synthesized by thermal oxidation with and without a gold film as a catalyst. The SEM images reveal wire-like and rod-shaped nanowhiskers about several hundred micrometers in length and 100 nm in diameter. The three observed Raman peaks at 474, 632, and 774 cm⁻¹ indicate the typical rutile phase which is in agreement with the X-ray diffraction results. The photoluminescence properties were measured at room temperature. The peaks at 342 nm corresponding to the excitation transitions from the conduction band to the valence band of the SnO₂ nanowhiskers were not observed. However, a strong emission band at 600 nm was detected indicating the existence of oxygen vacancies in both samples. A new emission band at 398 nm was also observed in the sample with the gold film and it could be attributed to the near band-edge emission.     

Simple synthesis and spectroscopic studies on cobalt added ZnO nanocrystals

Cobalt doped zinc oxide nanoparticles were prepared through simple wet chemical method. X-ray diffraction studies confirm the prepared particles are in wurtzite structure. Scanning Electron Microscopy studies show the shape and morphology of the particles. To identify the presence of cobalt in ZnO, Energy Dispersive X-ray analysis was done. Optical absorption measurements show the presence of exciton peak at 375 nm. Photoluminescence studies were done with the excitation wavelength of 330 nm, which shows the emission because of exciton recombination and oxygen vacancy.     

New diode laser-excitable green fluorescent label and its application to detection of bovine serum albumin via microchip electrophoresis

A novel amino-reactive fluorescent label is presented that is based on a yellow daylight chromophore and fluorophore. Its absorption band is wide and peaks at 431 nm in water solution, thus well matching the lines of either the 375-nm and the 431-nm diode lasers and of many frequency-variable dye lasers. When conjugated to bovine serum albumin (BSA), the fluorescence peaks at 501 nm with a quantum yield of 0.21. Its large Stokes' shift of 70 nm facilitates the discrimination of undesired excitation light which is particularly important for sensitive detection in miniaturized separation techniques such as microchip capillary electrophoresis (MCE). Unlike several other fluorophores, the fluorescence intensity of the new label is independent of pH over a broad range (3 to 9). The applicability of the label is demonstrated by labeling the amino acid lysine and the 66 kD protein BSA, and by separating BSA from the free label via MCE within 90 s. The limit of detection is in the order of 12 nM at an optically active path length of 20 µm.

     

Studies of Cu‐doped ZnS thin films prepared by sputtering technique

Radio frequency magnetron sputtering technique has been used to deposit Cu‐doped ZnS thin films on glass and n‐type Si(100) substrates at room temperature. Crystalline structure, surface morphology, and elemental oxidation states have been studied by X‐ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy. Ultraviolet–visible spectroscopy has been employed to measure the transmittance, reflectance, and absorbance properties of coated films. The deposited thin films crystallize in zinc blende or sphalerite phases as proved by X‐ray diffraction analysis. The intensity of diffraction peaks decreases with increasing the dopant concentrations. The predominant diffraction peak related to (111) plane of ZnS is observed at 28.52° along with other peaks. The peak positions are shifted to higher angles with an increase of Cu concentrations. X‐ray photoelectron spectroscopy studies show that Cu is present in +1 oxidation state. Transmittance, reflectance, and absorbance properties of the deposited films have a slight variation with dopant concentrations. Copyright © 2016 John Wiley & Sons, Ltd.     

Study of electrodeposited zinc selenide (ZnSe) nanostructure thin films for solar cell applications

Electrodeposition approach was used to grow the ZnSe nanostructure on indium doped tin oxide (ITO) layered glass substrate. Due to low cost and high degree of absorption, binary semiconductors made from chalcogens such as CdSe, ZnO, ZnS and ZnSe provide significant features in photovoltaic and photoelectrochemical cells. The structural and morphological properties of deposited nanostructures were examined by XRD and SEM. X-ray diffraction analysis informed about cubic structure with a preferred orientation and the calculated crystal size was approximately 75 nm. The optical properties were examined by UV–visible absorbance spectra and optical band gap was measured using Tauc plot. The deposited ZnSe nanostructure has direct band gap ∼2.52 eV at room temperature which was less than 2.82 eV which is the band gap of bulk ZnSe. Investigations also focused on additional qualities like excellent optical transmission, low electrical resistance, and good photosensitivity. Because of the presence of defect states in the deposited nanostructure, the band gap energy is smaller than that of bulk material. The current-voltage characteristics were measured in dark mode and under illumination of normal tungsten filament light and LED. There was notable change in the current for both normal light and LED in comparison to dark mode. The findings of all the characterization methodologies suggested that for the production of solar cells low cost ZnSe may be used as an alternative environment friendly Cd-free window layer.     

XRD and AFM studies of ZnS thin films produced by electrodeposition method

The structure and morphology of ZnS thin films were investigated. ZnS thin films have been grown on an indium tin oxide glass substrate by electrodeposition method using zinc chloride and sodium thiosulfate solutions at room temperature. The X-ray diffraction patterns confirm the presence of ZnS thin films. From the AFM images, grain size decreases as the cathodic potential becomes more negative (from ?1.1 to ?1.3 V) at various deposition periods. Comparison between all the samples reveals that the intensity of the peaks increased, indicating better crystalline phase for the films deposited at ?1.1 V. These films show homogeneous and uniform distribution according to AFM images. On the other hand, XRD analysis shows that the number of ZnS peaks increased as deposition time was increased from 15 to 30 min at ?1.1 V. The AFM images show thicker films to be formed at ?1.1 V indicating more favourable condition for the formation of ZnS thin films.     

Low-temperature growth and photoluminescence property of ZnS nanoribbons

At a low temperature of 450 degrees C, ZnS nanoribbons have been synthesized on Si and KCl substrates by a simple chemical vapor deposition (CVD) method with a two-temperature-zone furnace. Zinc and sulfur powders are used as sources in the different temperature zones. X-ray diffraction (XRD), selected area electron diffraction (SEAD), and transmission electron microscopy (TEM) analysis show that the ZnS nanoribbons are the wurtzite structure, and there are two types-single-crystal and bicrystal nanoribbons. Photoluminescence (PL) spectrum shows that the spectrum mainly includes two parts: a purple emission band centering at about 390 nm and a blue emission band centering at about 445 nm with a weak green shoulder around 510 nm.     

The effect of different gas atmospheres on the structure,morphology and photoluminescence properties of pulsed laser deposited Y3(Al,Ga)5O12:Ce3+ nano thin films

Luminescent properties of Y₃(Al,Ga)₅O₁₂:Ce³⁺ phosphor powder and thin films were obtained. The phosphor powder was used as target material for Pulsed Laser Deposition (PLD) of the thin films in the presence of different background gases. Excitation peaks for the powder were obtained at 439, 349, 225 and 189 nm and emission peaks at 512 and 565 nm. X-ray diffraction indicated that better crystallization took place for films deposited in a 20 mTorr O₂ atmosphere. Atomic force microscope revealed an RMS value of 0.7 nm, 2.5 nm and 4.8 nm for the films deposited in vacuum, O₂ and Ar atmospheres, respectively. The highest PL intensity was observed for films deposited in the O₂ atmosphere. A slight shift in the wavelength of the PL spectra was obtained for the thin films due to a change in the crystal field. The thickness of the films varied from 120 nm to 270 nm with films deposited in vacuum having the thin layer and those in Ar having the thick layer. The stoichiometry of the powder was maintained in the film during the deposition as confirmed by Rutherford backscattering spectroscopy.     

水热法制备ZnS∶Cu,Al纳米X射线发光粉及其光谱特性

采用水热法低温(200 ℃)处理12 h直接制备ZnS∶Cu, Al纳米晶, 并探讨其光致(PL)和X射线激发(XEL)光谱特性及后续退火处理的影响. XRD和TEM分析表明, 水热法直接制备的ZnS∶Cu, Al粒径约为15 nm, 尺寸分布窄, 分散性好, 具有纯立方相的球形结构. 其PL和XEL光谱均为宽带谱, n(Cu)/n(Zn)=3×10^-4和n(Cu)/n(Al)= 0.5时PL和XEL光谱强度最大, XEL峰值在470 nm处. 在此条件下, 水热处理3 h直接合成的纳米晶在氩气保护下于800 ℃退火1 h后样品的XEL发光进一步增强. XEL光谱强度约是退火前样品的8倍, 此时峰值波长在520 nm, 团聚形成径为200～500 nm的类球形六方相结构. 发光强度增强, 但粒径很小, 对提高成像系统分辨率非常有意义. 通过比较样品的XEL和PL光谱, 讨论了XEL和PL光谱的发光机理和激发机制及退火对其特性的影响.