As-synthesized Quantum Dots Research Articles

Anion-Driven Bandgap Tuning of AgIn(SxSe1-x)2 Quantum Dots.

Accurate tuning of the electronic and photophysical properties of quantum dots is required to maximize the light conversion efficiencies in semiconductor-assisted processes. Herein, we report a facile synthetic procedure for AgIn(SxSe1-x)2 quantum dots with S content (x) ranging from 1 to 0. This simple approach allowed us to tune the bandgap (2.6-1.9 eV) and extend the absorption of AgIn(SxSe1-x)2 quantum dots to lower photon energies (near-IR) while maintaining a small QD size (∼5 nm). Ultraviolet spectroscopy studies revealed that the change in the bandgap is modulated by the electronic shifts in both the valence band and the conduction band positions. The negative overall charge of the as-synthesized quantum dots enabled us to make films of quantum dots on mesoscopic TiO2. Excited state studies of the AgIn(SxSe1-x)2 quantum dot films demonstrated a fast charge injection to TiO2, and the electron transfer rate constant was found to be 1.5-3.5 × 1011 s-1. The results of this work present AgIn(SxSe1-x)2 quantum dots synthesized by the one-step method as a potential candidate for designing light-harvesting assemblies.

Ultra-small cesium silver bismuth bromide quantum dots fabricated by modified hot-injection method for highly efficient degradation of contaminants in organic solvent

Lead-free halide perovskite material has drawn fast-growing interest due to its superior solar-conversion efficiency and nontoxic nature. In this work, we have successfully fabricated cesium silver bismuth bromide (Cs2AgBiBr6) quantum dots utilizing the hot injection method. The as-synthesized quantum dots were characterized by combined techniques, which showed remarkable visible-light photocatalytic activity for organic dyes and antibiotic degradation in ethanol. Specifically, about 97% of rhodamine B and methyl orange may be removed within 10 min and 30 min, respectively. Additionally, 60% of antibiotic residue of tetracycline hydrochloride is degraded in 30 min which is 7 times more than that on commercial titania (P25). The reactive species for the photodegradation are determined through capture experiments, and a reaction mechanism is proposed accordingly. This work provides a novel photocatalyst for the selective removal of diverse organic contaminants in ethanol and an alternative for the potential application of lead-free halide perovskites.

Fabrication of Epoxy-CuInS-ZnS QDs- nanocomposite for fluorescent, transparent toughened coating applications

We herein report a simple method for preparing luminescent and highly toughened transparent epoxy/copper indium sulfide-zinc sulfide (CIS-ZnS) nanocomposite for coating applications. Briefly, fluorescent organically soluble dodecanethiol-capped CIS-ZnS core–shell quantum dots (QDs) was prepared via a solvothermal method. The as-synthesized QDs were small, spherical and highly crystalline, with an average particle diameter of 2.7 nm and improved photoluminescence quantum yields. The QDs were then dispersed in an epoxy matrix to producealuminescent, transparent, and toughened nanocompositewith excellent mechanical properties: 5348.45 ± 58 J/m2 impact strength value (90 % better thanepoxy system only), 34.6 ± 2.8 MPa tensile strength and 6.55 ± 0.31% elongation at break value (significant increment compared to the neat epoxy system). The proposed method is facile and efficient in preparing luminescent, transparent and toughened surface coating materials, which could be used for various physical and automobile applications.

Facile aqueous synthesis of ZnCuInS/ZnS–ZnS QDs with enhanced photoluminescence lifetime for selective detection of Cu(ii) ions

Abstract Quaternary quantum dots (QDs) have recently gained more attention due to their low toxicity, tunable wavelength, reduced or no blueshift emission upon overcoating, improved photoluminescence (PL) quantum yield, and PL lifetime when compared to their binary (II–VI) and ternary (I–III–VI) counterparts. In this work, the aqueous synthesis of ZnCuInS/ZnS–ZnS multi-shell quaternary QDs as a nanosensor for the selective detection of Cu2+ ions was reported. The as-synthesized QDs were spherical, with a particle diameter of 3.66 ± 0.81 nm, and emitted in the first near-infrared window (725 nm) with an average decay PL lifetime of 43.69 ns. The X-ray diffraction analysis showed that the QDs were of the wurtzite structure, while the Fourier transform infrared spectroscopy confirmed GSH capping through the sulphur–metal bond. Furthermore, the fluorometric study shows that the developed multi-shell QDs were selective towards Cu2+ ions compared to other metal ions via fluorescence quenching with a limit of detection of 1.4 µM, which is below the acceptable limit in drinking water.

Cd1-xDyxS semiconductor quantum dots: Structure, optical properties and energy transfer parameters

Dy3+ ions doped into CdS (Cd1-xDyxS) semiconductor quantum dots (QDs) were successfully synthesized using a wet chemical method. The presence of Dy3+ ions in CdS QDs was verified using Energy Dispersive X-ray spectroscopy (EDX). X-ray Diffraction (XRD) and absorption spectral analyses revealed that the as-synthesized QDs had a Wurtzite (WZ) structure with a particle size of approximately 4–5 nm. The optical properties of Dy3+ ions, ligand asymmetry and nature of the Dy3+-ligand bond in Cd1-xDyxS QDs were studied using excitation spectroscopy, photoluminescence (PL) spectroscopy and PL lifetime. The energy transfer processes from CdS host to Dy3+ ions and between Dy3+ ions, as well as the nature and mechanism of these processes were studied and explained in detail. The results of the analysis of CIE Chromatic coordinate diagram show that the Cd1-xDyxS QD is potential candidates for lighting applications because they can emit white light with suitable Dy concentration.

Size-tunable bismuth quantum dots for self-powered photodetectors under ambient conditions

Although black phosphorus analogue, bismuthene, has been extensively investigated in recent years, yet the investigation into the photoelectronic devices is still in its infancy. In this contribution, uniform zero-dimensional (0D) bismuth (Bi) quantum dots (QDs) with different sizes were successfully synthesized by a simple solvothermal method. The as-synthesized 0D Bi QDs serve as working electrode materials by a direct deposition for photoelectrochemical (PEC)-type photodetection. The PEC results demonstrate that the as-fabricated 0D Bi QD-based electrode not only possess suitable self-powered broadband photoresponse, but also displays excellent photodetection performance. Under simulated light, the photocurrent density and photoresponsivity of the as-fabricated 0D Bi QD-based electrode can reach 2690 nA cm−2, and 22.0 μA W−1, respectively. In addition, the as-prepared Bi QDs with the average diameter of 17 nm exhibit the best PEC photoresponse behavior in the studied size range of Bi QDs, mainly ascribed to the synergistic effect of suitable band gap and accessible active sites. It is anticipated that the uniform Bi QDs can be served as building blocks for a variety of photoelectronic devices, further expanding the application prospects of bismuthene, and can provide in-depth acknowledge on the performance optimization of monoelement Bi-based optical devices.

Synthesis, optical, structural and biocompatibility assessment of red-emitting CuInS[formula omitted]-ZnS quantum dots conjugated to folic acid

Bioconjugation of nanoparticles is a hot topic of research for a wide range of biological applications, particularly in cancer diagnosis and treatment. In this study, we report the synthesis of glutathione capped CuInS2/ZnS quantum dots (QDs) in an aqueous medium followed by folic acid (FA) modification to produce CIS-ZnS/FA conjugates. The as-synthesized QDs were small, with an average particle diameter of 2.3 nm, and emit in the red region, which was retained even after conjugation with FA. The formation of the conjugates was investigated by ultraviolet–visible (UV–Vis) absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. The conjugate were then analyzed for their cytotoxicity against both folate receptor (FR) positive (HeLa) and FR negative (A549, C26) cancer cell lines. The results of this study revealed the highly biocompatible nature of the CIS-ZnS/FA conjugates towards both FR positive and negative cancer cell lines and thus they are of potential use in biological applications.

Selective and sensitive detection of Cu2+ ions in the midst of other metal ions using glutathione capped CuInS2/ZnS quantum dots

We herein report a facile fluorometric method for the detection of Cu 2+ ions by using water-soluble glutathione (GSH) capped ternary CuInS 2 /ZnS (CIS/ZnS) quantum dots (QDs). The as-synthesized QDs are ∼3.2 nm in diameter, nearly spherical in shape and fluorescent in the red region. Photostability studies revealed that the as-synthesized CuInS 2 /ZnS QDs maintained 70% of their initial fluorescence after hours of irradiation while the pH analysis showed that the QDs fluorescent emission was stable within the pH 4–11 with maximum stability at pH 6. The fluorometric analysis revealed that the QDs undergoes remarkable photoluminescence quenching in the presence of Cu 2+ ions compared to other metal ions such as Hg 2+ , Co 2+ , Cd 2+ , Pb 2+ , Zn 2+ , Ni 2+ , Mg 2+ , Sn 2+ , Mn 2+ , Fe 2+ , Fe 3+ ions. The Fourier transform infra-red (FTIR) spectroscopy, Dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses revealed that the quenching could be attributed to the aggregation of QDs due to the complexation of Cu 2+ ions with the GSH capping group of the QDs. The fluorescence quenching of CIS/ZnS QDs exhibited linear response against Cu 2+ ions in the concentration range of 75–750 nM with a detection limit of 63 nM. These results reveled that GSH capped CIS/ZnS QD sensor could be a potential fluorescent probe for the detection of Cu 2+ ions in aqueous solutions .

Mechano-optical Modulation of Excitons and Carrier Recombination in Self-Assembled Halide Perovskite Quantum Dots.

Mechanically modulating optical properties of semiconductor nanocrystals and organic molecules are valuable for mechano-optical and optomechanical devices. Halide perovskites with excellent optical and electronic properties are promising for such applications. We report the mechanically changing excitons and photoluminescence of self-assembled formamidinium lead bromide (FAPbBr3) quantum dots. The as-synthesized quantum dots (3.6 nm diameter), showing blue emission and a short photoluminescence lifetime (2.6 ns), form 20-300 nm 2D and 3D self-assemblies with intense green emission in a solution or a film. The blue emission and short photoluminescence lifetime of the quantum dots are different from the delayed (ca. 550 ns) green emission from the assemblies. Thus, we consider the structure and excitonic properties of individual quantum dots differently from the self-assemblies. The blue emission and short lifetime of individual quantum dots are consistent with a weak dielectric screening of excitons or strong quantum confinement. The red-shifted emission and a long photoluminescence lifetime of the assemblies suggest a strong dielectric screening that weakens the quantum confinement, allowing excitons to split into free carriers, diffuse, and trap. The delayed emission suggests nongeminate recombination of diffusing and detrapped carriers. Interestingly, the green emission of the self-assembly blueshifts by applying a lateral mechanical force (ca. 4.65 N). Correspondingly, the photoluminescence lifetime decreases by 1 order of magnitude. These photoluminescence changes suggest the mechanical dissociation of the quantum dot self-assemblies and mechanically controlled exciton splitting and recombination. The mechanically changing emission color and lifetime of halide perovskite are promising for mechano-optical and optomechanical switches and sensors.

Study of optical properties and energy transfer mechanism of Tb3+, Sm3+ singly doped and co-doped ZnS quantum dots

For the first time, Tb3+ and Sm3+ ions co-doped into semiconductor ZnS quantum dots (QDs) were successfully synthesized by a wet chemical method. The presence of Tb3+ and Sm3+ ions in ZnS QDs was verified by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) and UV–visible absorption spectra analyses revealed that the as-synthesized QDs had a zinc blende (ZB) structure with a particle size of about 3–4 nm. The optical properties of Sm3+ ions in ZnS QDs were studied through the excitation, photoluminescence (PL) spectroscopy, and PL-decay lifetime by using the Judd-Ofelt (J-O) theory. The luminescent quenching phenomenon of Sm3+ was observed when its concentration was higher than a specified value. For the ZnS QDs co-doped Tb3+ and Sm3+, the luminescent intensity of Sm3+ ions was enhanced because of the energy transfer (ET) process from Tb3+ ions to Sm3+ ions. The main interaction mechanism for the Tb3+-Sm3+ and Sm3+-Sm3+ energy transfer processes was determined by using the Inokuti-Hirayama (I–H) model.

Green Synthesis of Sodium Alginate Capped -CuInS2 Quantum Dots with Improved Fluorescence Properties.

CuInS2 (CIS) quantum dots (QDs) are known to be ideal fluorophores based on their low toxicity and tunable emission. However, due to low quantum yield (QY) and photostability, the surface is usually passivated by a higher bandgap shell (e.g. ZnS). This always resulted in a blue-shifted emission position which is not usually favourable for biological imaging. To address this problem, we herein report the passivation of green synthesized near infra-red emitting glutathione (GSH) capped CuInS2 QDs using different concentration of sodium alginate (SA) at different temperatures. The as-synthesized QDs are small (~ 3.2nm), highly crystalline and emitted in the near infra-red region. The optical results showed a 36% increase in photostability and a 2-fold increase in quantum yield at ratio 1:8 (SA: CIS) which is suitable for prolonged biological imaging applications. Transmission electron microscope and X-ray diffraction (XRD) analyses showed that the materials are highly crystalline without any change in shape and size after passivation with the biopolymer. Graphical Abstract.

A solution-processed ZnO quantum dots ultraviolet photodetector with high performance driven by low operating voltage

Solution-processed zinc oxide (ZnO) ultraviolet (UV) photodetector with high performance has great potential in practical applications. In this letter, ZnO quantum dots with diameters ranged in 4–6 nm were synthesized by a facile solution method. The results showed that the as-synthesized quantum dots were wurtzite structured ZnO and had specific surface area as high as 68.3 m2/g. Also, a solution-processed ZnO quantum dots-based ultraviolet photodetector was built. This UV photodetector exhibited a good photoresponse to 365 nm UV light at low operating voltage, under 48 μW/cm2 UV illumination, the responsivity (R), photocurrent gain (G), response time (Tr) and decay time (Td) of the photodetector were 21.6 A/W at 3.6 V, 85.8 at 4.0 V, 1.9 s and 51.1 s, respectively.

Lysine-Functionalized Tungsten Disulfide Quantum Dots as Artificial Enzyme Mimics for Oxidative Stress Biomarker Sensing.

The color generating from the biochemical reaction between 3,3′,5,5′-tetramethylbenzidine and Lysine@WS2 QDs was used a signal for the detection of hydrogen peroxide. The QDs were prepared using a combination of techniques, that is, probe sonication and hydrothermal treatment. Analysis via UV–vis spectroscopy, Fourier transform infrared and Raman spectroscopy, X-ray diffraction, energy-dispersive spectroscopy, and transmission electron microscopy yielded detailed information on the nature and characteristics of these quantum dots. Furthermore, as-synthesized quantum dots were studied for their capability to mimic peroxidase enzyme using 3,3′,5,5′-tetramethylbenzidine as a substrate. Consequently, a colorimetric sensor utilizing Lysine@WS2 QDs could detect hydrogen peroxide in a range of 0.1–60 μM with a response time of 5 min. The same material was used for H2O2 detection using impedance spectroscopy, which yielded a dynamic range of 0.1–350 μM with a response time of 30–40 s.

Synthesis and optimization of emission characteristics of water-dispersible ag-in-s quantum dots and their bactericidal activity

Developing novel aqueous-soluble quantum dots (QDs) can create new opportunities for better biological utilization. In the present work, novel, high emissive and biocompatible N-acetyl-L-cysteine-capped Ag-In-S QDs (as an I-III-VI structure) were prepared in a facile and straightforward way. The dominance of the strong confinement regime was observed due to the very small size of nanoparticles, which was smaller than their excitonic Bohr radius. To prepare reproducible Ag-In-S QDs, their emission characteristics were improved by optimizing the experimental variables which resulted in the enhancement of their emission quantum yield to near 32% at 615 nm. The absorption and emission results support the contribution of band edge-independent radiative recombination pathways for charge carriers in the prepared Ag-In-S QDs. The possible mechanisms for such donor-acceptor recombination were also discussed. To explore the antibacterial ability of the Ag-In-S QDs, their bactericidal activity was evaluated against different types of Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli and Salmonella enterica) bacteria. Precise measurements confirmed a remarkable bactericidal activity of Ag-In-S QDs against the different pathogenic bacteria even at low concentration of QDs (15 μg/mL). It was found that the QDs are more effective on Gram-negative bacteria. While the preparation method was simple and cost-effective, the as-synthesized QDs were highly emissive and stable with significant antibacterial activity. This demonstrates the great potential of present Ag-In-S QDs for future hygienic and medical purposes.

Comparative Studies on the Aqueous Synthesis and Biocompatibility of L-Cysteine and Mercaptopropionic Acid Capped CdSe/CdS/ZnS Core/Shell/Shell Quantum Dots.

Quantum dots have now become the most important candidates and widely exploited as promising architectures for use as diagnostic and imaging agents in biomedicine and as semiconductors in the electronics industry. This article emphasizes on the aqueous synthesis of water soluble CdSe/CdS/ZnS core/shell/shell quantum dots with L-cysteine and mercaptopropionic acid as capping agent and their observed properties have been compared. The biocompatibility of the assynthesized quantum dots have also been analyzed through the cytotoxicity study using MTT assay. The structural, morphological and optical properties of these quantum dots have been examined through X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV-Visible absorption spectroscopy (UV-Vis) and Photoluminescence spectroscopy (PL). The capping of L-cysteine and mercaptopropionic acid on the quantum dots has been confirmed from Fourier transform infrared spectroscopy (FTIR). XRD results demonstrated the formation of hexagonal wurtzite structure for L-cysteine and cubic zinc blende structure for mercaptopropionic acid capped CdSe/CdS/ZnS quantum dots. From the optical measurements, it is observed that there is a considerable increase in the photoluminescence intensity of L-cysteine capped quantum dots than MPA. The HRTEM images revealed the narrow size distribution and in addition, L-cysteine capped quantum dots were found to be more biocompatible than mercaptopropionic acid capped quantum dots which would provide new opportunities for applications in bioimaging and biolabelling.

Rapid sonochemical water-based synthesis of functionalized zinc sulfide quantum dots: Study of capping agent effect on photocatalytic activity.

This study presents a rapid water-based chemical precipitation method for synthesis of zinc sulfide (ZnS) quantum dots (QDs), under the ultrasonic radiation, using two capping agents; including 2-mercaptoethanol and l-cysteine. It is demonstrated that by applying ultrasonic radiation, the synthesis time can be significantly decreased. The effect of capping agent type on the color specifications (using colorimetry), absorption spectra (using ultraviolet-visible absorption spectroscopy) and ZnS structure (using X-ray diffraction) are investigated. The results of the research indicate that the as-synthesized QDs were cubic structures with dimensions less than 10 nm. After characterization, the QDs samples were performed as nano-scaled photoatalysts, through a UV-driven photodegradation process for the degradation of crystalline violet (CV) as a pollutant dye. Moreover, the present study assesses the effect of operating conditions including the pH of the dye solution, UV-irradiation time, ionic strength, type and dosage of nanophotocatalyst on degradation efficiency. Experimental results of the research demonstrate the QDs can be reused for at-least five times, without a significant decrease in their photocatalytic properties. The maximum photodegradation efficiency for the CV solution adjusted at pH 11, in the presence of a low amount of QDs (i.e. 5 mg) was observed after 90 min irradiation time. Finally, the probable mechanism and kinetics of degradation reaction are proposed in the study. From the kinetic data, the acceptable regression coefficient values (>0.98) for the pseudo first-order kinetic model was obtained for expression the present QD-based photodegradation approach.

Cell viability study of green synthesized CdTe/CdSe quantum dots against osteosarcoma cell line for improved therapeutic action

Abstract

One-step Aqueous Synthesis of Zn-based Quantum Dots as Potential Generators of Reactive Oxygen Species

AbstractThe actual incorporation of dopant species into the ZnS Quantum Dots (QDs) host lattice will induce structural defects evidenced by a red shift in the corresponding exciton. The doping should create new intermediate energetic levels between the valence and conduction bands of the ZnS and affect the electron-hole recombination. These trap states would favour the energy transfer processes involved with the generation of cytotoxic radicals, so-called Reactive Oxygen Species, opening the possibility to apply these nanomaterials in cancer research. Any synthesis approach should consider the direct formation of the QDs in biocompatible medium. Accordingly, the present work addresses the microwave-assisted aqueous synthesis of pure and doped ZnS QDs. As-synthesized quantum dots were fully characterized on a structural, morphological and optical viewpoint. UV-Vis analyzes evidenced the excitonic peaks at approximately 310 nm, 314 nm and 315 nm for ZnS, Cu-ZnS and Mn-ZnS, respectively, Cu/Zn and Mn/Zn molar ratio was 0.05%. This indicates the actual incorporation of the dopant species into the host lattice. In addition, the Photoluminescence spectrum of non-doped ZnS nanoparticles showed a high emission peak that was red shifted when Mn2+ or Cu2+ were added during the synthesis process. The main emission peak of non-doped ZnS, Cu-doped ZnS and Mn-doped ZnS were observed at 438 nm, 487 nm and 521 nm, respectively. Forthcoming work will address the capacity of pure and Cu-, Mn-ZnS quantum dots to generate cytotoxic Reactive Oxygen Species for cancer treatment applications.

High throughput process for the continuous preparation of quantum dots using fluid dynamically controlled reactor

Scale-up of synthesis process is highly required for commercial application of quantum dots (QDs). Although batch-type hot injection method is most popular synthesis route for QDs, its commercial scale-up version only gives non-uniform and less luminescent QDs with broad size distribution. In this study, we introduce a novel and facile method of large-scale synthesis of QDs using a fluid-dynamically controlled reactor, Taylor-Couette reactor (TCR). We successfully synthesized CdSe QDs with TCR and as-synthesized QDs were capped with epitaxial CdS layers using the molecular precursors for enhanced luminescence. The synthesis process was stabilized after 20 min from the start of initial injection of precursors and standard deviation of luminescence wavelength and spectral linewidth was less than 1 nm. After shell capping process based on pyrolysis of Cd-diethyldithiocarbamate, CdSe QDs synthesized from continuous processing route based on TCR showed intense photoluminescence at 640 nm with a spectral linewidth of 33 nm, which is much narrower than PL spectra of QDs synthesized from conventional batch-type synthesis route using reaction vessel with large volume capacity. We demonstrated high throughput synthesis of highly luminescent CdSe QDs using TCR as a platform for continuous synthesis with very large production yield (22,560 kg‧day−1‧m−3 in space-time yield).

Optically sensitive I-V properties of CdS and CdS:Cu quantum dots

CdS and CdS:Cu quantum dots are synthesized by chemical method using 3-mercaptopropionic acid (MPA) as capping material. The samples are then characterized using different structural and chemical characterization techniques which confirms nanoformation of the samples. The as-synthesized quantum dots are used to fabricate simple devices on glass substrate by depositing Aluminium (Al) electrodes on the active quantum dot layer with thermal evaporation technique. The current-voltage (I-V) relationship of the quantum dot devices are investigated under dark, room light and laser light (Red-638.2 nm) conditions and enhancement in photocurrent with increase in light intensity is observed for the devices.