Doping Of ZnS Research Articles

Antimicrobial and electrical properties of ce‐ and ni‐doped zns nanoparticles obtained by a sonochemical method

AbstractIn this work, cerium‐ and nickel‐codoped ZnS nanoparticles were obtained by a sonochemical method for 20 min. The nanoparticles were characterized by X‐ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), and microscopy electronic transmission (MET). The electrical properties are estimated through I‐V curves and the antimicrobial activity was analyzed against E. coli (gram‐negative) and S. aureus (gram‐positive) bacteria using the diffusion disk methodology. The diffractograms indicate the obtaining of cubic structure ZnS for the pure sample, whereas the doped samples present the cubic and hexagonal structures of the ZnS. The bandgap reduced from 3.60 to 3.52 eV, for pure and codoped samples. I‐V curves indicate an increase in resistivity with doping, being more evident for samples containing cerium. Antimicrobial activity increased as doping occurred, where the codoped sample showed the best results. Even for the low amount of dopant (1 mol%), the antimicrobial activity can be increased by about 50% for the codoped sample, compared to the pure ZnS. Thus, it is known that the doping of ZnS with cerium and nickel provides the stabilization of the hexagonal metastable phase, which acts to restrict electronic mobility and, consequently, improves the antimicrobial response of the material.

Фотолюминесценция низкоразмерных композитных структур полиметилметакрилат/(Zn,Cd,Mn,Eu)S

A colloidal technology for the synthesis and doping of low-dimensional structures based on zinc and cadmium sulfides directly in the medium of an acrylic monomer is implemented in the process of obtaining optically transparent compositions of polymethylmethacrylate/(Zn,Cd,Mn,Eu)S. It is shown that the photoluminescence of the compositions is associated with a system of levels of structural defects of semiconductor particles located in its band gap, which are formed during successive doping of ZnS and CdS layers with Mn2+ and Eu3+ ions, and with intraband 5D0 → 7F1,2,4 transitions of 4f-electrons of Eu3+ ions. Photoluminescence excitation it occurs as a result of the transition of electrons from the valence band of a semiconductor to the levels of defects in its structure and partial energy transfer to the excited energy levels of Eu3+ ions.

Photoluminescence of Polymethylmethacrylate/(Zn,Cu,Ag)S:Eu3+ Compositions

Luminescent (Zn,Cu,Ag)S:Eu3+ nanoparticles (quantum dots, QDs) are synthesized upon decomposition of thioacetamide metal complexes in methylmethacrylate during block polymerization upon heating. The QD formation is confirmed by a corresponding band in the optical absorption spectrum of polymer compositions. Photoluminescence of polymethylmethacrylate/(Zn,Cu,Ag)S:Eu3+ compositions manifests itself as a complex band, related to crystal structure defects formed during doping of ZnS with copper and silver ions, and a set of narrow luminescence bands of Eu3+ ions. The luminescence is excited due to the interband transition and electronic transitions from the valence band to ZnS defect levels and intrinsic energy absorption by Eu3+ ions. The bond between Eu3+ ions and ZnS particles is confirmed by the dependence of the ZnS broadband luminescence intensity on the Eu3+ ion concentration and the increase in the intensity of the narrowband luminescence of Eu3+ ions as a result of energy transfer from the doped ZnS crystal levels to the energy levels of Eu3+ ions.

Improvement of Power Conversion Efficiency of Quantum Dot-Sensitized Solar Cells by Doping of Manganese into a ZnS Passivation Layer and Cosensitization of Zinc-Porphyrin on a Modified Graphene Oxide/Nitrogen-Doped TiO2 Photoanode.

It is vital to acquire power conversion efficiencies comparable to other emerging solar cell technologies by making quantum dot-sensitized solar cells (QDSSCs) competitive. In this study, the effect of graphene oxide (GO), nitrogen, manganese, and a porphyrin compound on the performance of QDSSCs based on a TiO2/CdS/ZnS photoanode was investigated. First, adding GO and nitrogen into TiO2 has a conspicuous impact on the cell efficacy. Both these materials reduce the recombination rate and expand the specific surface area of TiO2 as well as dye loading, reinforcing cell efficiency value. The maximum power conversion efficiency of QDSSC with a GO N-doped photoelectrode was 2.52%. Second, by employing Mn2+ (5 and 10 wt %) doping of ZnS, we have succeeded in considerably improving cell performance (from 2.52 to 3.47%). The reason for this could be for the improvement of the passivation layer of ZnS by Mn2+ ions, bringing about to a smaller recombination of photoinjected electrons with either oxidized dye molecules or electrolyte at the surface of titanium dioxide. However, doping of 15 wt % Mn2+ had an opposite effect and somewhat declined the cell performance. Finally, a Zn-porphyrin dye was added to the CdS/ZnS by a cosensitization method, widening the light absorption range to the NIR (near-infrared region) (>700 nm), leading to the higher short-circuit current density (JSC) and cell efficacy. Utilizing an environmentally safe porphyrin compound into the structure of QDSSC has dramatically enhanced the cell efficacy to 4.62%, which is 40% higher than that of the result obtained from the TiO2/CdS/ZnS photoelectrode without porphyrin coating.

Photoluminescence of Zn1 – х – yCuxEuyS/EuL3 Quantum Dots in a Polyacrylate Matrix

Zinc sulfide is one of the most popular luminescent semiconductors of the А(II)B(VI) group. Doping of ZnS quantum dots (QDs) with Ln3+ ions makes it possible to form in a semiconductor matrix nanosized structures containing isolated narrowband luminescence centers. Incorporation of QDs into ac-rylate matrices additionally stabilized particles and allows formation of their morphology. The Zn1 ‒ x ‒ yCuxEuyS/EuL3 nanosized structures, where L is a trifluoroacetate anion, are synthesized in situ in methylmethacrylate (MMA) by the method of appearing reagents. Doping of ZnS was performed by introduction of soluble zinc sulfide precursors simultaneously with copper and europium trifluoroacetates into the acrylate reaction mixture. The optically transparent polymer composites PММА/Zn1 – x – yCuxEuyS/EuL3 were obtained by radical casting polymerization of MMA. The excitation of luminescence in the composites is related to electronic interband transitions in ZnS, to the system of levels formed by dopant ions in the ZnS band gap, and to the intrinsic energy absorption by Eu3+ ions. The broadband luminescence of the composites is caused by intracrystalline defects formed in ZnS upon doping. The narrowband luminescence results from the 5D0 → 7Fj electronic transitions of Eu3+ ions bound to QDs and existing in the polymer matrix independently of them. The energy transfer from the donor levels of the semiconductor matrix to the levels of Eu3+ with subsequent luminescence is confirmed by the overlap of the absorption bands of doped ZnS and the luminescence excitation bands of the composites, as well as by an increase in the intensity of the narrowband luminescence of Eu3+ simultaneously with a decrease in the intensity of the broadband recombination luminescence of doped ZnS. The decrease in the intensity of the recombination luminescence of ZnS with increasing concentration of Eu3+ to >1.0 × 10–3 mol/L is also related to the formation of a layer of europium complex compounds on the surface of particles, which hinders the propagation of exciting radiation to the particle core.

Optical and structural investigation of ZnS:Cu thin films synthesized by spray pyrolysis

We have investigated the effect of Cu dopant and substrate temperature on the structural and optical properties of ZnS thin films deposited on glass substrate by spray pyrolysis technique. The glass substrate temperature varied from 300 to 450 °C. Different characterization methods such as X-ray diffractometry, EDS, SEM, and Raman scattering analyses for studying the structural, morphological and optical properties of the prepared ZnS and ZnS:Cu samples were carried out. Improvement in crystallization, increase in crystallite size and also better growth orientation along the (111) direction are clearly evident due to the increase in the substrate temperature. Cu doping effects on the displacement of diffraction peaks towards larger angles and decrease in crystallite size which caused by this impurity are the main results of this studies. The absence of any other impurity in samples, smooth surface, homogenous structure and spherical shape of crystals have approved by EDS analysis and SEM imagining, respectively. Raman scattering spectra of ZnS and ZnS:Cu in ambient condition not only indicate E and A Raman first order scattering of ZnS, but also indicate an intense peak about 334 cm−1 related to surface optical phonon mode in this nanostructure. Optical properties of thin films determined by UV–Vis spectroscopy and the energy band gap was calculated with ZnS doping rates. Photoluminescence analysis and origin of green emission peak at 533 nm and red peak at 745 nm were discussed.

Detection and discrimination of α- and β-radiation with plastic scintillators based on pulse shape discrimination

There is a need for more convenient and effective methods for detecting and discriminating between α- and β-radiation. In this work, two plastic scintillator detectors were used to detect and discriminate between α- and β-radiation based on digital pulse shape discrimination (PSD) . The charge comparison method (CCM) performed better than the time comparison method (TCM), and Detector A (with ZnS doping) showed better results than those of Detector B (without ZnS doping). With Detector A, the total rate of misidentification was approximately 0.25% with the appropriate discrimination parameters; with Detector B, the total rate of misidentification was approximately 1.5%. Both detectors showed improved discrimination compared with most commercial detectors. This method is a promising means for improving the effectiveness of the detection and discrimination of α- and β-radiation based on PSD.

Construction of MoS2 nano-heterojunction via ZnS doping for enhancing in-situ photocatalytic reduction of gold thiosulfate complex

Recovery of gold thiosulfate complex ([Au(S2O3)2]3−) from leaching solutions has been recognized as a tough task, which limited the industrial promotion of eco-friendly thiosulfate leaching technique. In this work, MoS2/ZnS nano-heterojunction as a catalyst was proposed for the recovery of [Au(S2O3)2]3− from leaching solution. The results indicated that [Au(S2O3)2]3− could not only be efficiently recovered, but also in-situ reduced into Au0 when MoS2/ZnS nano-heterojunction being used in the leaching solution. Mo0.45Zn0.10S exhibited an extremely high reduction capacity (1120.56 mg/g), which was 4.52 and 1.72 times of ZnS and MoS2, respectively. The great improvement was resulted from the ZnS doping on MoS2, which brought stronger light absorption, higher transferred efficiency and lower recombination of photogenerated electron-hole pairs of MoS2. In addition, the Au0 could completely desorpt from MoS2/ZnS nano-heterojunctions in Na2S solution in less than 4 min, leading MoS2/ZnS nano-heterojunction to have remarkable cycling performances. This work provided a new insight for enhancing the recovery and in-situ reduction of gold thiosulfate complex from leaching solutions.

Фотолюминесценция квантовых точек Zn-=SUB=-1-x-y-=/SUB=-Cu-=SUB=-x-=/SUB=-Eu-=SUB=-y-=/SUB=-S/EuL-=SUB=-3-=/SUB=- в полиакрилатной матрице

Zinc sulfide is one of the most popular luminescent semiconductors of group A(II)B(VI). Doping ZnS quantum dots with Ln3+ ions makes it possible to form nanoscale structures in a semiconductor matrix containing isolated centers of narrow-band luminescence. The introduction of quantum dots into the acrylate matrix further stabilizes the particles and allows them to form their morphology. Nanoscale structures of Zn1-x-yCuxEuyS/EuL3, where L − trifluoroacetate are anions, were synthesized by the method of emerging reagents in situ in the medium of methyl methacrylate (MMA). ZnS doping was performed by simultaneous introduction of soluble precursors of zinc sulfide, as well as copper and europium trifluoroacetates into the acrylate reaction mixture. Polymer optically transparent compositions of PMMA/Zn1-x-yCuxEuyS/EuL3 were obtained by radical polymerization of MMA in the block. The excitation of luminescence of compositions is associated with Interzone electron transitions in ZnS, with a system of levels that form alloying ions in the forbidden zone of ZnS, as well as with their own energy absorption by Eu3+ ions. Broadband luminescence of compositions is caused by intracrystalline defects formed in ZnS during doping. Narrow-band luminescence occurs as a result OF 5D0→7Fj electronic transitions in Eu3+ ions associated with quantum dots, as well as being in the polymer matrix independently of them. The transfer of energy from the donor levels of the semiconductor matrix to the levels of Eu3+ ions, followed by its release in the form of luminescence, was confirmed by the imposition of absorption bands doped with ZnS and excitation bands of luminescence compositions, as well as an increase in the intensity of narrow-band luminescence of Eu3+ ions while reducing the intensity of a wide band of recombination luminescence of doped ZnS. A decrease in the intensity of the ZnS recombination luminescence band with an increase in the concentration of Eu3+ >1.0∙10-3 mol/L ions is also associated with the formation of a layer of complex europium compounds on the particle surface that prevent the passage of exciting radiation to the particle core.

The optical behavior of multi-emission quantum dots based on Tb-doped ZnS developed via solvothermal route for bioimaging applications

Quantum dots (QDs), semiconducting nanocrystals with exceptional photo-physical characteristics, have become one of the prevailing class of multifunctional nanodevices and imaging probes. The engineering of QD probes became an essential step for successful clinical applications in real-life. In this work, a water soluble and highly luminescent semiconducting QDs are developed via solvothermal route. Terbium was used as a dopant to replace the Zn in the ZnS nanocrystals. Various concentrations of Tb, from 0 to 6 at.%, was doped into the ZnS. The influence of Tb dopant on the crystal structure of the ZnS and diameter of the formed nanocrystals was investigated using X-ray diffraction and transmission electron microscopy. The optical properties were studied using the UV–vis spectrophotometer, which showed a red shift of the optical band gap. The luminescence properties showed that the doping of ZnS with 6at.% of Tb ions resulted in a remarkable enhancement of the luminescence intensity and the quantum yield. This sample showed three distinctive light emissions (blue, green and red) when excited at 320 nm, 360 nm and 390 nm. The obtained results embarked that the developed QDs may be employed as efficient bio-imaging probe for practical clinical applications in real-life, which is confirmed in this article for the first time.

Fabrication of CdS quantum dot sensitized solar cells using nitrogen functionalized CNTs/TiO2 nanocomposites

Effect of using nitrogen functionalized carbon nanotubes in photoanode materials of quantum dot sensitized solar cells (QDSSCs) was studied. Several SWCNT/TiO2, MWCNT/TiO2 and N-doped MWCNT/TiO2 nanocomposites were prepared including different weight percents (0.25–0.40wt%) of CNTs to TiO2. The nanocomposites were applied as the photoanodes of QDSSCs. All photoanodes were fabricated by CdS and ZnS doping using successive ionic layer adsorption and reaction (SILAR) method. The measured optical band gaps of all photoanodes were approximately equal to 2.5eV. The photoluminescence (PL) spectra of all photoanode nanocomposites illustrated four maxima at around 310, 365, 440 and 535nm plus two shoulders near 285 and 720nm which could be assigned to the emission bands of TiO2, CdS and ZnS nanoparticles (NPs) as well as CNTs. The highest power conversion efficiency (η) was measured under one illumination of sun (AM 1.5, 100mW/cm2) for the 0.35% N-MWCNT loaded cell (1.78%) indicating 24.47% increase in the η value relative to that of the cell made up of bare TiO2 (1.43%). The IPCE of 0.35% N-MWCNT was the greatest (~54% near 450nm) among other cells containing 0.35% of SWCNT and MWCNT indicating it can convert the most incident light into electrical energy due to the most loading of CdS quantum dots on the N-MWCNT. The electrochemical impedance spectroscopy (EIS) evidenced that the Rs of the photoanode including 0.35%N-MWCNT (23.78Ω) was smaller than that of the blank photoanode (32.28Ω) and this was due to the increased charge transfer in the nanocomposite photoanode. Besides, a greater recombination resistance (R2) was measured for the 0.35% N-MWCNT photoanode (494.2Ω) compared with that of the bare TiO2 photoelectrode (206.8Ω).

Effect of Indium doping on the photoelectrochemical and photocatalytic properties of zinc sulphide

In this article, the visible light enhanced photoelectrochemical and photocatalytic properties for nano-sized Indium doped Zinc Sulphide compared to undoped ZnS had been reported. Both ZnS and In doped ZnS (In-ZnS) were synthesized through soft chemical route by a co-precipitation method. ZnS and In doped ZnS existed as single phase having cubic structure. These samples were nano-sized with a particle size of approximately 24nm. SEM images revealed the presence of aggregated particles with a wide distribution in the particle size. UV–visible Diffused Reflectance Spectra showed improved visible light absorption for the doped sample as compared to the undoped sample. X-ray photoelectron studies indicated the presence of indium as In3+ in In-ZnS. Photoluminescence studies suggested the presence of both zinc and sulfur vacancies in these samples. After the doping of ZnS with In, there was an increase in photocurrent under visible light irradiation. The doped sample also exhibited enhanced photocatalytic activity for hydrogen generation. A good correlation between photocatalytic and photoelectrochemical properties was seen for both ZnS and In doped ZnS. The improvement in In doped ZnS has been attributed to the increased visible light absorption arising due to the decreased band gap of the doped sample.

Formation of Cu-related emission centers under thermal doping of ZnS powders with CuCl and CuCl2

The photoluminescence (PL), PL excitation and electron paramagnetic resonance spectra of powderlike ZnS doped with Cu from CuCl and CuCl2 compounds at 800°C with restricted access of atmospheric air or in He flow were investigated. It is shown that the contribution of blue and green PL bands to PL spectra depends on the compounds used for doping and on the annealing conditions. The appearance of Cu clusters on the surface of ZnS microcrystals for both doping compounds is found. These clusters manifest themselves in the presence of broad line in electron paramagnetic resonance spectra and are the additional source for the doping of ZnS powder. The chemical reactions upon doping are analyzed. It is shown that these reactions control the concentration of the recombination centers responsible for blue and green PL bands and are also the reason of Cu clusters appearance. Under annealing in He flow when volatile components are removed by flowing gas, the dominant process can be the doping of ZnS from Cu clusters. This allows obtaining the blue band mainly. The localization of recombination centers responsible for blue and green emissions is discussed.

Absorption Induced by Mn Doping of ZnS for Improved Sensitized Quantum-Dot Solar Cells

Absorption Induced by Mn Doping of ZnS for Improved Sensitized Quantum-Dot Solar Cells

Features of ZnS-powder doping with a Mn impurity during synthesis and subsequent annealing

Luminescence, electron spin resonance, and X-ray diffraction (XRD) methods were used to investigate the features of ZnS-powder doped by Mn impurity during self-propagating high-temperature synthesis and subsequent annealing. The obtained powder consists of ZnS microcrystals with mainly hexagonal phase (80 ± 5)%. It was found, that after synthesis Mn presents not only in the form of non-uniformly distributed microscopic impurities in ZnS, but also in the form of Mn metal nanocrystals. Thermal annealing at 800°C leads to the additional doping of ZnS from metallic Mn, to the redistribution of the embedded Mn in the volume of microcrystals, and to the ZnS oxidation. At the same time, the ratio between the cubic and hexagonal phases does not change. It was shown that annealing causes a decrease in the concentration of the defects responsible for the luminescence-excitation bands, which correspond to transitions from the ground to the excited states of the Mn2+ ion. As a result of annealing, there is also a change in XRD coherent domain size. Simultaneously, the intensity of peaks in the luminescence-excitation spectrum with wavelengths of 375 and 395 nm was changed. The causes of these changes and the nature of the corresponding bands are discussed.

First-principles calculations reveal the n-type doping difficulties of group IIIA elements in zinc blende ZnS

At present, the n-type doping behavior of ZnS is still under debate. Some groups have reported that it is difficult to obtain low-resistivity n-type ZnS, while others think it is easy. Our first-principles calculations on the n-type doping of group IIIA elements strongly support the former viewpoint. We find that, although AlS−i, GaS−i, and InS−i are shallow donors, their formation energy is very high at the conduction band minimum (CBM). Thus they can not contribute to the n-type conductivity. Other impurities are all deep donors with high formation energy at the CBM, thus having no contributions either. We believe that our results can provide an understanding of the difficulties of n-type doping of ZnS.

Native point defects in ZnS: First-principles studies based on LDA, LDA + U and an extrapolation scheme

First-principles calculations based on LDA, LDA+U and an extrapolation scheme are performed to study the native point defects in zincblende ZnS, and the three methods give similar results. Zinc vacancies in the 2− charge state have extremely low formation energy at the conduction band minimum (CBM), thus they will heavily compensate the n-type doping of ZnS. In Zn-rich conditions, sulfur antisites and zinc interstitials in the zinc cage sites are compensating centers in p-type ZnS. Sulfur vacancies and sulfur intersitials in the zinc cage sites are negative-U centers. We compare our results with previous reports and obtain some new findings.

Competitive Performance of Carbon “Quantum” Dots in Optical Bioimaging

Carbon-based “quantum” dots or carbon dots are surface-functionalized small carbon nanoparticles. For bright fluorescence emissions, the carbon nanoparticles may be surface-doped with an inorganic salt and then the same organic functionalization. In this study, carbon dots without and with the ZnS doping were prepared, followed by gel-column fractionation to harvest dots of 40% and 60% in fluorescence quantum yields, respectively. These highly fluorescent carbon dots were evaluated for optical imaging in mice, from which bright fluorescence images were obtained. Of particular interest was the observed competitive performance of the carbon dots in vivo to that of the well-established CdSe/ZnS QDs. The results suggest that carbon dots may be further developed into a new class of high-performance yet nontoxic contrast agents for optical bioimaging.

AX centers in II-VI semiconductors: Hybrid functional calculations

Hybrid functional calculations predict significantly enhanced stability of AX centers against shallow acceptors in selected II-VI semiconductors (ZnO, ZnS, and ZnSe), as compared to the calculations based on local density approximation and generalized gradient approximation. The results agree well with the experimental observations on the p-type doping of ZnS and ZnSe. The improved description of the AX centers by hybrid functional calculations is due to the correction of the valence band maximum of the semiconductor.

The bipolar doping of ZnS via native defects and external dopants

By employing first-principle total-energy calculations, a systematic study of the dopability of ZnS to be both n- and p-types compared with that of ZnO is carried out. We find that all the attempted acceptor dopants, group V substituting on the S lattice site and group I and IB on the Zn sites in ZnS, have lower ionization energies than the corresponding ones in ZnO. This can be accounted for by the fact that ZnS has relative higher valence band maximum than ZnO. Native ZnS is weak p-type under S-rich condition, as the abundant acceptor VZn has rather large ionization energy. Self-compensations by the formation of interstitial donors in group I and IB-doped p-type ZnS can be avoided when sample is prepared under S-rich condition. In terms of ionization energies, LiZn and NS are the preferred acceptors in ZnS. Native n-type doping of ZnS is limited by the spontaneous formation of intrinsic VZn2−; high efficient n-type doping with dopants is harder to achieve than in ZnO because of the readiness of forming native compensating centers and higher ionization energy of donors in ZnS.