Properties Of ZnS Quantum Dots Research Articles

Exploring the Effects of Various Capping Agents on Zinc Sulfide Quantum Dot Characteristics and In-vitro Fate.

The choice of capping agents used during the synthesis process of quantum dots (QDs) can significantly influence their fate and fundamental properties. Hence, choosing an appropriate capping agent is a critical step in both synthesis and biomedical application of QDs. In this research, ZnS QDs were synthesized via chemical precipitation process and three commonly employed capping agents, namely mercaptoethanol (ME), mercaptoacetic acid (MAA), and cysteamine (CA), were used to stabilize the QDs. This study was aimed to examine how these capping agents impact the physicochemical and optical characteristics of ZnS QDs, as well as their interactions with biological systems. The findings revealed that the capping agents had considerable effects on the behavior and properties of ZnS QDs. MAA-QD exhibited superior crystal lattice, smaller size, and significant quantum yield (QY). In contrast, CA-QDs demonstrated the lowest QY and the highest tendency for aggregation. ME-QDs exhibited intermediate characteristics, along with an acceptable level of cytotoxicity, rapid uptake by cells, and efficient escape from lysosomes. Consequently, it is advisable to select capping agents in accordance with the specific objectives of the research.

Optical Properties of ZnS Quantum Dots: Applications in Solar cells and Biomedicine

Optoelectronics and optical filter applications require wide bandgap semiconductors as photo-anode and surface passivation layers in sensitized solar cells and biomedical and biosensors fields such as optical filters [1–4]. Selecting suitable wide bandgap semiconductors increases the valuable implementation of desired devices. However, bulk semiconductors harvest only a particular spectrum, QDs help in harvesting large radiation spectra because of the tunable bandgap. Also, aqueous-based methods are eco-friendly, economical, biocompatible, and non-toxic. Therefore, in this study, ZnS quantum dots (QDs) were synthesized at 9.5 pH and 70 ͦ C temperature using an aqueous-based chemical route method. A comparative study was presented using hydrazine hydrate and ammonium chloride as reducing agents for Zinc precursor and 3-mercaptopropionic acid (MPA) as capping agents. Confinement was achieved in ZnS using MPA as a stabilizer. Optical properties were studied using a photoluminescence (PL) spectrophotometer where photoluminescence (PL) shows emission behavior and photoluminescence excitation (PLE) shows excitation behavior of ZnS. Emission peaks were observed at 386 nm in as-prepared ZnS NPs and at 316 nm in confined QDs. Sharp band edge luminescence and the possibility to confine ZnS NPs show its eligibility in optoelectronics and optical filters in biological applications.

Cation co-doping into ZnS quantum dots: towards visible light sensing applications

Efficient and environmentally benign visible light responsive materials have been sought after owing to their interesting applications such as visible light photocatalysis, visible light water splitting and visible light sensing. In this research study, the effect of co-doping on the absorption and electrical properties of ZnS quantum dots is studied. Upon co-doping of Fe and Cu into ZnS quantum dots, a new absorption band in the visible region is observed. Furthermore, these quantum dots show photoresponse in the visible region unlike their undoped counterparts that is only effective in the UV region, suggesting their utility in light sensing applications.

Effect of Mg and Cu doping on structural, optical, electronic, and thermal properties of ZnS quantum dots

Undoped and 10% Mg or Cu-doped ZnS quantum dots (Zn0.9Mg0.1S and Zn0.9Cu0.1S) were prepared by a simple chemical method at low temperature (300 °C). The effect of doping on structural characteristics was investigated using Rietveld profile method and the high-resolution transmission electron microscope techniques. Differential scanning calorimetry (DSC) scans were recorded in the temperature range 23–600 °C with different heating rates (5 to 30 °C/min). The model-free isoconversional method was applied to explore the effect of doping on the reaction and the growth mechanism of nano-ZnS. Diffuse UV reflectance revealed an increase of the optical energy gap upon doping with Mg, while it decreased as ZnS was doped with Cu. The change in energy gap upon doping was explained using density function theory calculation. The photoluminescence (PL) spectra revealed violet, blue, green colors depended on the composition and excitation wavelength used in the study. The intensity of PL has been increased for doped samples compared with pristine ZnS. Tuning the energy gap of ZnS through doping enable applications for light-harvesting and photocatalytic degradation in the visible region.

The effect of cobalt ions doping on the optical properties of ZnS quantum dots according to photoluminescence intensity and crystalline structure

The doping of Co2+ into ZnS QD offered a considerable luminescence intensity in the UV region and controlling of the Quantum Dot (QD) size. A performed X-ray diffraction (XRD) study revealed a cubic phase of the d-spacing 0.32 nm for a Co2+ concentration level of 0.005. The grain size varied between 3.9 nm and 7.5 nm for concentrations between 0.001 and 0.01. The obtained photoluminescence (PL) spectrum revealed a dependence of emission intensity and QD bandgap on the dopant concentration. With the help of TEM imaging, it has been shown that the size of the QD was about 4.8 nm. Prepared bulk samples of the Zn0.1-xSCox, with 0.001 < x < 0.01 have bandgap energies that varied from 2.69 eV for the concentration 0.001 down to 2.46 eV for 0.01. The calculated QD size ranged from 5.84 nm to 4.46 nm, which verified the QD size dependence on the dopant concentration and confirmed quantum confinement.

Tailoring the optical, magnetic, and photocatalytic properties of ZnS quantum dots by rare-earth ion doping

Gd-doped ZnS quantum dots (QDs) were synthesized through a hydrothermal route. The energy gap of ZnS QDs could be tuned as a function of the Gd doping concentration. The room-temperature electron paramagnetic resonance spectra of the Gd-doped ZnS QDs showed two resonance signals at g ≈ 2.052 and 2.813, which were attributed to the Gd (III) ions located at sites with weak and intermediate crystal fields, respectively. In addition, the as-synthesized Zn0.49Gd0.01S and Zn0.47Gd0.03S QDs displayed well-defined room-temperature ferromagnetism. The photocatalytic degradation rates of all the fabricated samples were assessed on the phenol red dye under the UV light illuminations.

Structural, Morphological, Vibrational, Thermal and Optical Properties of ZnS Quantum Dots in the Polymer Matrix

Background: Nanotechnology is believed to be a future for new human generations. Among different emerging materials, the Nanocomposites (NCs) would be on front line. The aim of the current study is provide a way to synthesize the ZnS-polyacrylamide NCs with emphasis on the effect of aging on polymer due to its various physical properties. Objective: To prepare and study the properties of ZnS-Polymer NCs with drying time in polymer matrix. Methods: ZnS-polyacrylamide NCs samples were synthesized by adding aqueous suspension of ZnS Nanoparticles (NPs) in Sol of acrylamide: bisacrylamide copolymer. These samples were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), UV-Vis, and Photoluminescence (PL) spectroscopy. Results: From XRD data analysis, nano phase and zinc blend structure of the material are confirmed. From SEM images, the pristine ZnS NPs show spherical morphology, and this texture is still preserved in the polymer composites. FT-IR confirms that there is a strong interaction between polymer chain and ZnS NPs. The TGA results indicate that the incorporation of the NPs impacts the thermal properties of the ZnS-polymer NCs and displays higher thermal stability than the pure polymer matrix. The optical data predicts the band gap and Quantum Confinement Effect (QCE) and reduction of ZnS NPs within the polymer matrix. These NCs show emission in blue region with decreases in intensity with drying time. Conclusion: ZnS NPs incorporated in polyacrylamide were prepared by copolymer technique. Structural analysis confirms zinc blend structure. The vibration spectra of composites samples predicts an interaction between different functional groups of polymer with the metal sulfide. These NCs show enhanced thermally stability. The observed optical band shows a red shift and quantum confinement effect. The size calculated by XRD and optical data shows good correlation with each other. The PL spectra of the NCs exhibits a broad blue emission with excitation (λex = 320 nm). The visible region emission could be originated from the radiative recombination, involving defect states within the ZnS nanocrystals energy band.

Effect of Eu2+ doping on structural, optical, magnetic and photovoltaic properties of ZnS quantum dots

ZnS and Eu2+: ZnS QDs with different doping concentrations were prepared by co-precipitation method at room temperature. It was observed that all samples form in cubic structure. The Eu2+ (0.1%): ZnS, Eu2+ (0.3%): ZnS and Eu2+ (0.5%): ZnS QDs display broad photoluminescence emission peaks at 513.5 nm, 511. 7 nm and 510.6 nm, respectively, are related to the Eu2+ intra-ion transition of 4f6d1 – 4f7. The M-H measurements indicated that unlike ZnS QDs, Eu2+: ZnS QDs with different doping concentrations indicates ferromagnetic behavior at room temperature. The incident photon to electron conversion efficiency (IPCE) is improved with the Eu2+ doping, which proposes the QD solar cell efficiency is able to be boosted by Eu2+ doping by reason of broadened absorption spectra. Accordingly, the data point out that Eu2+: ZnS QDs with different doping concentrations are able to be appropriate materials for photovoltaic and spintronic applications.

Influence of Fe2+ and Ni2+ contents on the optical and electrical properties of ZnS quantum dots

The work reports a well controlled synthesis of un-doped and Fe2+ and Ni2+ doped ZnS quantum dots (QDs) based highly luminescent of pure cubic zinc blende structure. The samples were characterized for structural, morphological, optical and electrical parameters and great care has been made in correlating all these properties. The optimum concentrations of Zn1−xFexS and Zn1−xNixS dopants were found to be x = 0.2 for superior optical and electrical properties. Incorporation of Fe2+ or Ni2+ into ZnS lattice have generated acceptor level as an isolated state just above the valence band of ZnS, and hence electron requiring less excitation energy for transferring from the acceptor level to the conduction band. Moreover, it was found that the PL emission intensity of Fe2+ doped ZnS QDs is higher than that of Ni2+ doped. The results indicated that the active luminescent centers created by dopants and localized surface plasmon resonance energy transfer of ZnS QDs significantly increased with Fe2+ ions into the ZnS lattice. Over all in light of the results obtained during the study, the doped samples can have potential for function in vast variety of applications.

Effects of Cu Dopant on Lattice and Optical Properties of ZnS Quantum Dots.

Doped and undoped ZnS colloidal nanocrystals have drawn much attention due to their versatile applications in the fields of optoelectronics and biotechnology. In this paper, Cu doped ZnS quantum dots were synthesized via the simple thermolysis of ethylxanthate salts. The lattice and optical properties of the nanocrystals were then studied in detail. The quantum dot lattice contracted linearly between Cu concentrations of 0.2-2%, while it continued to contract more gradually as Cu concentrations were further increased from 4 to 6%, due in part to the Cu ions located on the surface of the ZnS lattice. Cu incorporation induces a long tail in absorption at long wavelengths. The PL spectrum shows a red shift at first, and then a blue shift with increases in Cu concentration. Cu doped at low concentrations (0.2-1%) enhanced the emission, while high Cu concentrations (2-6%) quenched emissions.

Influence of cobalt concentration on structural and optical properties of ZnS quantum dots

ZnS and Co-doped ZnS nanoparticles have been prepared by simple chemical precipitation method. Zinc acetate, sodium sulfide, and cobalt nitrate have been used as precursors for the preparation of Co-doped ZnS quantum dots. The X-ray diffraction results revealed that the undoped and Co-doped ZnS quantum dots exhibit hexagonal structure. The average grain size of quantum dot was found to lie in the range of 2.6–3.8 nm. The surface morphology has been studied using scanning electron microscope. The compositional analysis results confirm the presence of Co, Zn and S in the sample. The optical properties of undoped and Co-doped ZnS quantum dots have been studied using absorption spectra. TEM results show that undoped and Co-doped ZnS nanoparticles exhibit a uniform size distribution with average size of 2.5–3.4 nm.

Functionalization and characterization of ZnS quantum dots using biocompatible l-cysteine

In this work, the functionalization of ZnS quantum dots using the thiol group of l-cysteine for different concentrations has been reported. Chemical precipitation method was used for the synthesis of nascent as well as l-cysteine functionalized ZnS quantum dots for optimized values of pH and molar concentrations of the precursors. Morphological studies were done by X-ray diffraction (XRD) and TEM. Optical measurements were done by UV–visible, Fourier transform infrared (FTIR) and energy resolved photoluminescence studies. Particle size was calculated by using Brus equation. Appreciable changes in morphological and optical properties of ZnS quantum dots were observed in few cases. XRD results shows that, the primary crystallite size decreases with increasing the capping concentration, however, the crystal structure remain same for all the used concentrations of l-cysteine. UV–visible analysis shows that band gap and particle size is also tunable with l-cysteine capping. FTIR studies confirmed l-cysteine capping on the surface of quantum dots. As l-cysteine is non toxic and stable compound, the surface modification of ZnS quantum dots with l-cysteine not only prevents the aggregation of quantum dots but also make them available for the interaction with the target materials and make them suitable for specific biomedical applications.

Investigation on one-pot hydrothermal synthesis, structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.

Synthesis and Properties of ZnS Quantum Dots by an Oil-Water Interface Method

Nowadays, novel synthesis routes of nanoparticles are attracting a considerable attention of relative scientists. In this work, monodispersed spherical ZnS quantum dots (QDs) were synthesized by an oil-water interface method. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Typical TEM images showed that the average size of ZnS QDs was 3.3 nm. The ZnS QDs with the largest yield and UV absorbance were obtained with the mole ratio of [S2-]/[Zn2+] = 1.2/1.0 at 100 degrees C. Based on the above results and the previous outstanding work for synthesis of monodispersed inorganic nanoparticles, the formation mechanism of the monodispersed ZnS quantum dots was proposed. Additionally, UV-vis absorption and photoluminescence (PL) spectra for Mn2+ and Eu3+ doped ZnS QDs were used to investigate their optical properties. Effects of Mn2+ and Eu3+ doping ratio on their optical properties were studied. The optimized doping ratio of Mn2+ and Eu3+ was 4.0 mol.% and 5.0 mol.%, respectively.

A detailed study of physical properties of ZnS quantum dots synthesized by reverse micelle method

In this article, zinc sulfide nanocrystal quantum dots were synthesized by reverse micelle method using polyvinyl pyrrolidone as surfactant. The various crystallite properties of these nanocrystals such as, size, d-spacing, lattice parameter, microstrain, intrinsic stress, X-ray density, specific surface area, dislocation density, porosity, and agglomeration number have been analyzed using X-ray diffraction spectrum. The transmission electron microscopy was used to calculate the size and monitoring morphology of the nanocrystals, while the scanning electron microscopy was utilized to investigate the surface morphology of nanoclusters. The various optical properties of zinc sulfide quantum dots such as absorption coefficient, extinction coefficient, optical band gap energy, Urbach energy, and threshold wavelength have been analyzed using UV-visible data. The photoluminescence was used to study the emission spectra of produced ZnS quantum dots. Moreover, Furrier Transform-Infrared studies revealed that ZnS quantum dots are pure.