Structural, optical and photoluminescence properties of ZnS: Cu nanoparticle thin films as a function of dopant concentration and quantum confinement effect

Multifunctional Cu:ZnS quantum dots for degradation of Amoxicillin and Dye Sulphon Fast Black-F and efficient determination of urea for assessing environmental aspects

This work is particularly aimed at the preparation of ZnS and Cu doped ZnS (Cu:ZnS) QDs by facile and easy technique, chemical precipitation method for the degradation of water pollutants and a simple scheme was proposed to prepare the urea-sensing system. The morphological and optical properties of the synthesized QDs was studied using high resolution transmission and scanning electron microscopes, X-ray diffraction, energy dispersive X-ray analysis, fluorescence and ultraviolet-visible spectroscopy, differential thermal and thermogravimetric analyses, Brunauer-Emmett-Teller analysis. The photocatalytic performance was systematically assessed by the photodegradation of an important pharmaceutical water pollutant, Amoxicillin (AMX) and a dye Fast Sulphon Black F (SFBF) in aqueous medium under UV light irradiation. Also, a very sensitive system was prepared by depositing the dots over an indium-tin-oxide (ITO) glass substrate for the sensing of biologically active molecule urea as it is an important monitor of public health in water and soil productivity. The results illustrated excellent photocatalytic efficiency (86.46% for AMX and 99.41% for SFBF) with stability up to four cycles of degradation reaction. The optimal photocatalyst dosage for achieving maximum removal of AMX was found to be 70 mg at a pH of 9.5, with a treatment time of 40 min. Similarly, for SFBF, the optimal photocatalyst dosage was determined to be 60 mg at pH 9, with a treatment time of 60 min. Further, the electrochemical analysis was done by fabricating Urease enzyme (UR)/Cu:ZnS QDs/ITO bioelectrode and then the fabricated bioelectrode, was utilized to determine the different concentrations of urea by cyclic voltammetry. Thus, the obtained limit of detection and sensitivity of the fabricated biosensing device for urea detection was obtained to be 0.0092 μM and 12 μA μM-1cm-2, respectively; under the optimized experimental conditions. Hence, it is anticipated that Cu:ZnS QDs can also successfully be applied as a promising material for fabrication of novel bioelectrode for urea determination and the biosensing platform is desirable and viable.

Application of Response Surface Methodology for Optimization of Nanosized Zinc Oxide Synthesis Conditions by Electrospinning Technique

Zinc oxide (ZnO) is a well-known semiconductor material due to its excellent electrical, mechanical, and unique optical properties. ZnO nanoparticles are widely used for the industrial-scale manufacture of microelectronic and optoelectronic devices, including metal oxide semiconductor (MOS) gas sensors, light-emitting diodes, transistors, capacitors, and solar cells. This study proposes optimization of synthesis parameters of nanosized ZnO by the electrospinning technique. A Box–Behnken design (BB) has been applied using response surface methodology (RSM) to optimize the selected electrospinning and sintering conditions. The effects of the applied voltage, tip-to-collector distance, and annealing temperature on the size of ZnO particles were successfully investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images confirm the formation of polyvinylpyrrolidone-zinc acetate (PVP-ZnAc) fibers and nanostructured ZnO after annealing. X-ray diffraction (XRD) patterns indicate a pure phase of the hexagonal structure of ZnO with high crystallinity. Minimal-sized ZnO nanoparticles were synthesized at a constant applied potential of 16 kV, with a distance between collector and nozzle of 12 cm, flow rate of 1 mL/h, and calcination temperature of 600 °C. The results suggest that nanosized ZnO with precise control of size and morphology can be fabricated by varying electrospinning conditions, precursor solution concentration, and sintering temperature.

A review on metal-doped chalcogenide films and their effect on various optoelectronic properties for different applications

Chalcogenide thin films have been investigated and explored in the last several decades to widen their use in optical, electronic, and optoelectronic device sectors. The phenomenon corresponding to different induced stimuli effects, doping foreign elements is the most productive and efficient way to improve their structural ability, optical characteristics, and electronic approaches. Based on that, metal doping has an enormous impact on the aspects and understanding of the mechanism inside the matrix. This review is mainly based on metal-doped chalcogenide thin films, their effect on various properties of the host materials, and several applications based on that. Thin films doped primarily with bismuth (Bi), antimony (Sb), silver (Ag), tin (Sn), and copper (Cu) were analyzed and discussed. Progress in understanding their structure, bonding, and properties within the matrix was also discussed. This paper also describes the importance and developments of these metal-doped thin films, their physicochemical aspects, and their applications in optoelectronic devices. Different potential applications of these metal-doped chalcogenide thin films in manufacturing technology-based optoelectronic devices, namely sensors, waveguides, switching devices, batteries, optical memories, etc., are also highlighted.

The schematic presentation of some metal-doped chalcogenide thin films.

Dithiocarbamates: Challenges, Control, and Approaches to Excellent Yield, Characterization, and Their Biological Applications

Progresses made in previous researches on syntheses of dithiocarbamates led to increase in further researches. This paper reviews concisely the challenges experienced during the synthesis of dithiocarbamate and mechanisms to overcome them in order to obtain accurate results. Aspects of its precursor's uses to synthesize adducts, nanoparticles, and nanocomposites are reported. Some common characterization techniques used for the synthesized products were assessed. Biological applications are also reported.

Engineering the Morphology and Configuration of Ternary Heterostructures for Improving Their Photocatalytic Activity

Heteronanomaterials composed of suitable semiconductors enable the direct conversion from solar power into clean and renewable energy. Ternary heterostructures with appropriate configuration and morphology possess rich and varied properties, especially for improving the photocatalytic activity and stability synchronously. However, suitable ternary heterostructure prototypes and facile while effective strategy for modulating their morphology and configuration are still scarce. Herein, various ternary ZnS-CdS-Zn(1-x)Cd(x)S heterostructures with tunable morphology (0 to 2 D) and semiconductor configurations (randomly distributed, interface mediated, and quantum dots sensitized core@shell heterostructures) were facilely synthesized via one-pot hydrothermal method resulting from the different molecular structures of the amine solvents. Semiconductor morphology, especially configuration of the ternary heterostructure, shows dramatic effect on their photocatalytic activity. The CdS sensitized porous Zn(1-x)CdxS@ZnS core@shell takes full advantage of ZnS, Zn(1-x)Cd(x)S and CdS and shows the maximal photocatalytic H2-production rate of 100.2 mmol/h/g and excellent stability over 30 h. This study provides some guidelines for the design and synthesis of high-performance ternary heterostructure via modulation of semiconductor configuration and morphology using one-pot method.

Quantum tunneling of magnetization in GaN:Mn nanoparticles

GaN:Mn nanoparticles with quantum tunneling of magnetization were synthesized successfully by DC arc discharge plasma without any catalyst or template.

Evidence of competition in the incorporation of Co2+and Mn2+ions into the structure of ZnTe nanocrystals

Glass-embedded Zn_1−x−yMn_xCo_yTe nanocrystals (withx= 0.01 andyvarying from 0.000 to 0.800) were successfully synthesized using a protocol based on the melting–nucleation synthesis route and herein investigated by several experimental techniques.

Optical and Structural Investigations of Manganese Doped ZnS/SiO2 Core-Shell Nanostructure

The paper reports room temperature synthesis of wurtzite type manganese doped ZnS nanostructures via colloidal technique. The reaction procedure found to play an important role in the crystal growth of ZnS . Surface encapsulation of ZnS by silica ( SiO 2) provides effective approach for uniform coating, where 3-Mercaptopropyl Tri methoxysilane (MPS) has been used for silica source as a capping molecule. The obtained silica coated ZnS nanocrystals were well dispersed with hexagonal wurtzite structure of core-shell particles size of about 15 nm. Aggregation of these nanoparticles has been promoted to special shaped structures, which are crystals of 8H wurtzite with prominent pyramidal morphology with curved faces. Growth phenomena of this wurtzite polytype of homologous series 8H is based on screw dislocations and exhibited optimal photoluminescence (PL) spectra.

Quantum dots as a possible oxygen sensor

Results of studies on optical properties of low toxicity quantum dots (QDs) obtained from copper doped zinc sulfate are discussed in the paper. The effect of copper admixture concentration and solution pH on the fluorescence emission intensity of QDs was investigated. Quenching of QDs fluorescence by oxygen was reported and removal of the oxygen from the environment by two methods was described. In the chemical method oxygen was eliminated by adding sodium sulfite, in the other method oxygen was removed from the solution using nitrogen gas. For elimination of oxygen by purging the solution with nitrogen the increase of fluorescence intensity with decreasing oxygen concentration obeyed Stern-Volmer equation indicating quenching. For the chemical method Stern-Volmer equation was not fulfilled. The fluorescence decays lifetimes were determined and the increase of mean lifetimes at the absence of oxygen support hypothesis that QDs fluorescence is quenched by oxygen.

Ce doping influence on the magnetic phase transition in In2S3:Ce nanoparticles

The classical thermally driven transition from supermagnetic to blocked supermagnetic and quantum phase transition from magnetic long-range order to quantum superparamagnetic state have been observed in ultrasmall In₂S₃:Ce diluted magnetic semiconductors.

Luminescence and Morphological Kinetics of Functionalized ZnS Colloidal Nanocrystals

This paper reports functionalized zinc sulphide (ZnS) semiconductor nanocrystals (quantum dots, approx., 2.5 nm) which are an important building block in self-assembled nanostructures. ZnS is functionalized by organic stabilizer Thio glycolic acid (TGA). The samples have been synthesized by colloidal technique at relatively low temperature (below 100°C) at an atmospheric pressure of 10−3 torr. Manganese (Mn) doping ions have been incorporated (doped) in ZnS host lattice and observed its effect on growth morphology and optical properties of ZnS colloidal nanocrystals. By XRD, SEM, TEM, and PL, the obtained cubic phase nanosized TGA-capped ZnS materials were characterized. The morphology of ZnS obtained at different temperatures are analyzed by SEM. The crystallite size of the ZnS nanoparticles was estimated from the X-ray diffraction pattern by using Scherrer’s formula (approximately 2.5 nm) which is confirmed by TEM. The estimated bandgap value of ZnS NC’s by ()2 versus plot was 4.89 eV. Gaussian fitting curve in photoluminescence (PL) spectra indicated room temperature emission wavelength range from 300 to 500 nm in undoped and Mn-doped ZnS, with different emission peak intensities, and suggested the wide band emission colours in visible and near UV region which has wider applications in optical devices.

Bleaching of Congo red in the presence of ZnS nanoparticles, with dopant of Co2+ ion, as photocatalyst under UV and sunlight irradiations

The bleaching of Congo red was studied in the presence of zinc sulphide nanoparticles doped with Co2+ ion. The nanoparticles of zinc sulphide, doped with cobalt, were synthesized by controlled coprecipitation in the presence of mercaptoethanol as a capping agent. The characterization of nanoparticles was studied using UV-Vis spectra, XRD pattern and SEM and TEM images. The size of the nanoparticles was determined to be 10-40 nm. A maximum dye degradation of 94% was obtained under UV irradiation for 120 min. Also, a destruction of 98% was achieved under sunlight irradiation in 12 h at the optimum conditions. The photoreactivity and reproducibility of the proposed photocatalyst was compared with Degussa P25. The photodegradation of Congo red was investigated in real water containing carbonate, bicarbonate and sulphate ions. The pseudo-first-order rate constant, k, was 2.2 x 10(-2) min(-1) and 2.9 x 10(-2) h(-1) under UV and sunlight irradiations, respectively.

ZnS:Cu,Co water-soluble afterglow nanoparticles: synthesis, luminescence and potential applications

Cu(2+) and Co(2+) co-doped zinc sulfide water-soluble nanoparticles (ZnS:Cu,Co) were prepared and their afterglow luminescence was observed and reported for the first time. The nanoparticles have a cubic zinc blende structure with average sizes of about 4 nm as determined by high-resolution transmission electron microscopy (HRTEM) and x-ray diffraction (XRD). In the photoluminescence, two emission peaks are observed at 470 and 510 nm. However, in the afterglow, only one peak is observed at around 525 nm. The blue emission at 470 nm is from surface states and the green emission at 525 nm is from Cu(2+). This means that Cu(2+) is responsible for the afterglow from the nanoparticles, while the co-doping of Co(2+) is critical for the afterglow because no afterglow could be seen without co-doping with Co(2+). The successful observation of the afterglow from water-soluble nanoparticles may open up new applications of afterglow phosphors in biological imaging, detection and treatment.

Tunable Visible Emission of Ag-Doped CdZnS Alloy Quantum Dots

Highly luminescent Ag-ion-doped Cd1-xZnxS (0 ≤ x ≤ 1) alloy nanocrystals were successfully synthesized by a novel wet chemical precipitation method. Influence of dopant concentration and the Zn/Cd stoichiometric variations in doped alloy nanocrystals have been investigated. The samples were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscope (HRTEM) to investigate the size and structure of the as prepared nanocrystals. A shift in LO phonon modes from micro-Raman investigations and the elemental analysis from the energy dispersive X-ray analysis (EDAX) confirms the stoichiometry of the final product. The average crystallite size was found increasing from 1.0 to 1.4 nm with gradual increase in Ag doping. It was observed that photoluminescence (PL) intensity corresponding to Ag impurity (570 nm), relative to the other two bands 480 and 520 nm that originates due to native defects, enhanced and showed slight red shift with increasing silver doping. In addition, decrease in the band gap energy of the doped nanocrystals indicates that the introduction of dopant ion in the host material influence the particle size of the nanocrystals. The composition dependent bandgap engineering in CdZnS:Ag was achieved to attain the deliberate color tunability and demonstrated successfully, which are potentially important for white light generation.

Reverse micelle-derived Cu-doped Zn(1-x)Cd(x)S quantum dots and their core/shell structure

Reverse micelle chemistry-derived Cu-doped Zn(1-x)Cd(x)S quantum dots (QDs) with the composition (x) of 0, 0.5, 1 are reported. The Cu emission was found to be dependent on the host composition of QDs. While a dim green/orange emission was observed from ZnS:Cu QDs, a relatively strong red emission could be obtained from CdS:Cu and Zn(0.5)Cd(0.5)S:Cu QDs. Luminescent properties of undoped QDs versus Cu-doped ones and quantum yields of alloyed ZnCdS versus CdS QDs are compared and discussed. To enhance Cu-related red emission of CdS:Cu and Zn(0.5)Cd(0.5)S:Cu core QDs, core/shell structured QDs with a wider band gap of ZnS shell are also demonstrated.

The two-step thermochemical growth of ZnS:Mn nanocrystals and a study of luminescence evolution

In this work we report a new thermochemical method for the synthesis of ZnS:Mn nanocrystals. Zn(NO(3))(2) and Na(2)S(2)O(3) were used as the precursors and Mn(NO(3))(2) was the source of impurity. Thioglycerol (TG,C(3)H(8)O(2)S) was also used as the capping agent and the catalyst of the reaction. Na(2)S(2)O(3) is a heat sensitive material which releases S species upon heating. Consequently, the reaction proceeds in temperatures higher than room temperature. The reaction was done in two steps. In the first step, the precursors were heated at 96 degrees C for an hour without TG. In the second step, TG was injected to the solution and the heating process was continued for longer heating durations. A fast growth occurred in the first 10 min after the addition of TG, resulting in a sample with a band edge located at 4.0 eV. The growth was followed by elimination of the sample's scattering and emergence and increase of the luminescence during the heating process. Transmission electron microscopy and x-ray diffraction analyses demonstrated round shaped cubic phase ZnS:Mn nanocrystals with an average size around 3.0 nm. The luminescence emerged from about 15 min after the addition of TG. The emission was located at around 585 nm, demonstrating the Mn incorporation inside the particles. The luminescence intensity increased with time and saturated during the second step of the heating process. Finally, we propose a model explaining the formation and changes in the scattering and luminescence characteristic of the ZnS:Mn nanoparticles. The model is based on the separation of the nucleation and growth steps of the synthesis in the first and second steps of the reaction. This separation directly affects the achievement of the luminescent ZnS:Mn nanocrystals.

Synthesis of Zn(1-x)Cd(x)S:Mn/ZnS quantum dots and their application to light-emitting diodes

3.6 nm sized Mn-doped Zn(1-x)Cd(x)S quantum dots (QDs) with the composition (x) of 1, 0.5, 0.2 and 0 were synthesized by a reverse micelle approach. The bandgap energy of Zn(1-x)Cd(x)S:Mn QDs was tuned to a higher energy by increasing the Zn content, and the actual composition of alloyed Zn(1-x)Cd(x)S:Mn QDs was found to be different from the solution composition. Consecutive overcoating of the Zn(1-x)Cd(x)S:Mn QD surface by a ZnS shell was done, and the core/shell structured QDs exhibited quantum yields of 14-30%, depending on the composition of the core QDs. Using CdS:Mn/ZnS QDs, orange and white light-emitting diodes (LEDs) pumped by a near-UV and blue LED chips, respectively, were fabricated and their optical properties are described.