Quaternary Quantum Dots Research Articles

Dual Ligand Strategy for Efficient and Stable Ag–In–Ga–S Aqueous Quantum Dots

AbstractIn recent years, Ag−In−Ga−S (AIGS) quaternary quantum dots (QDs) have garnered significant attention as a novel class of environmentally friendly and non‐toxic QDs. However, the hydrothermal synthesis method for aqueous QDs has been plagued by issues such as inconsistent size, subpar crystallinity, and low photoluminescence quantum yield (PLQY). Herein, we developed a dual ligand strategy based on the hard and soft acids and bases (HSAB) theory to synthesize aqueous AIGS QDs with an impressive PLQY of up to 64.3 %, currently the highest value among hydrothermal‐synthesized uncoated I–III–VI QDs. The QDs exhibit better crystallinity, narrow size distribution (3.07±0.31 nm), and remarkable stability. The mechanism underlying this dual ligand strategy was further elucidated, shedding light on the distinct influences of different ligands on the growth of QDs. The high PLQY contributes to the further application of aqueous AIGS QDs in luminescent displays and the field of biology. Meanwhile, this ligand strategy has broad reference significance for efficient preparation of other water‐soluble QDs.

Ionic liquid-assisted preparation of Ag–Zn–In–S quaternary quantum dot thin films and luminescence performance optimized by machine learning

Machine learning-assisted synthesis of new materials has been an ongoing hot topic. Luminescent Ag–Zn–In–S quaternary semiconductor quantum dot thin films have great application potential in many fields because of their excellent photoelectric performance. In this study, an environmentally friendly ionic liquid-assisted approach was employed to prepare high-performance Ag–Zn–In–S luminescent thin films, and machine learning methods were applied to screen the optimal preparation conditions. The photoluminescence (PL) performance, crystal structure, and morphology of the thin films were also been studied. The initial data set was obtained by high-throughput experiments. By comparing machine learning algorithms of Xgboost, Random Forest, Bagging, SVM, Extra Tree, and Gradient Boosting, the Random Forest achieved the best accuracy (r = 0.84, R2 = 0.847) and was selected to predict the optimal preparation conditions of Ag–Zn–In–S quaternary quantum dot thin films. The machine learning predicted results are in great agreement with the subsequent experimental results, which verifies the accuracy and effectiveness of the machine learning model. This study offers a theoretical foundation for preparing optimal inorganic quantum dot luminescent materials using machine learning.

Spectrally narrow band-edge photoluminescence from AgInS2-based core/shell quantum dots for electroluminescence applications.

This study presents a facile synthesis of cadmium-free ternary and quaternary quantum dots (QDs) and their application to light-emitting diode (LED) devices. AgInS2 ternary QDs, developed as a substitute for cadmium chalcogenide QDs, exhibited spectrally broad photoluminescence due to intrinsic defect levels. Our group has successfully achieved narrow band-edge PL by a coating with gallium sulfide shell. Subsequently, an intrinsic difficulty in the synthesis of multinary compound QDs, which often results in unnecessary byproducts, was surmounted by a new approach involving the nucleation of silver sulfide followed by material conversion to the intended composition (silver indium gallium sulfide). By fine-tuning this reaction and bringing the starting material closer to stoichiometric compositional ratios, atom economy was further improved. These QDs have been tested in LED applications, but the standard device encountered a significant defective emission that would have been eliminated by the gallium sulfide shells. This problem is addressed by introducing gallium oxide as a new electron transport layer.

Cadmium-Based Quantum Dots Alloyed Structures: Synthesis, Properties, and Applications.

Cadmium-based alloyed quantum dots are one of the most popular metal chalcogenides in both the industrial and research fields owing to their extraordinary optical and electronic properties that can be manipulated by varying the compositional ratio in addition to size control. This report aims to cover the main information concerning the synthesis techniques, properties, and applications of Cd-based alloyed quantum dots. It provides a comprehensive overview of the most common synthesis methods for these QDs, which include hot injection, co-precipitation, successive ionic layer adsorption and reaction, hydrothermal, and microwave-assisted synthesis methods. This detailed literature highlights the optical and structural properties of both ternary and quaternary quantum dots. Also, this review provides the high-potential applications of various alloyed quantum dots.

High selectivity and fluorescence reversible Eu3+ sensor based on GSH-capped AgZnInS QDs.

Fluorescence sensors for trivalent europium ions (Eu3+) are seldom reported. We study the synthesis of water-soluble quaternary quantum dots (QDs) and investigate their fluorescence sensor application for detecting Eu3+ The as-synthesized glutathione (GSH)-capped AgZnInS (AZIS) QDs show great sensitivity and selectivity to Eu3+among 12 different metal cations. Detailed experimental results indicate that the fluorescence response of the AZIS QDs to increasing concentration of Eu3+ ([Eu3+]) include intensity quenching and peak wavelength blueshift. With the addition of OH-, the fluorescence response reverses. Electron transfer is considered to be the mechanism for the fluorescence quenching and peak wavelength blueshift of the GSH-capped AZIS QDs. Our work provides a new, to the best of our knowledge, method for the detection of Eu3+.

InGaAsSb/GaAsSb quantum dot structures

This work studies the modal gain from I n x G a 1 − x A s y S b 1 − y / G a A s S b $I{n_x}G{a_{1 - x}}A{s_y}S{b_{1 - y}}/GaAsSb$ quaternary quantum dots (QD) structures at different mole fractions of the structure. The quaternary structures are more flexible in attaining lattice-matching systems. First, the In- and As-mole fractions are varied. Four In-mole fractions are studied ( x = 0.01 , 0.03 , 0.05 , $(x\; = \;0.01,\;0.03,\;0.05,\;$ and 0.07), and their emitted wavelengths cover the range 571.4 − 5000 nm $571.4 - 5000\ {\rm nm}$ . Both In- and the As-mole fraction increment results in a red-shifted wavelength. Doping is also investigated where the structures are exhibited five times increment of modal gain, and the wavelength is blue-shifted under doping. A multi-peak behaviour is exhibited by these structures, which is essential in applications for choosing the required wavelength. These results promise that these structures can work in UV, visible, and infrared (IR) wavelength ranges.

Facile High-Yield Synthesis of Ag–In–Ga–S Quaternary Quantum Dots and Coating with Gallium Sulfide Shells for Narrow Band-Edge Emission

Among cadmium-free quantum dots (QDs), ternary or quaternary chalcogenide semiconductor QDs composed of groups 11, 13, and 16 elements have extensively been studied. Herein, monodispersed quaternary nanoparticles of silver indium gallium sulfide (AgInxGa1–xS2) are synthesized by a new route that specifically produces the target product without solid byproducts. The difference in the reactivity between groups 11 and 13 metals with chalcogen is a common issue in synthesizing the groups 11, 13, and 16 ternary or quaternary semiconductor QDs. Instead of a common approach to suppress the reactivity of group 11 metals, this study utilizes their high reactivity; rapid injection of a Ag source into the solution containing a thiocarboxylate produced small Ag2S nanoparticles. These Ag2S nanoparticles are then exposed to indium-, gallium-, and sulfur-containing species in situ and then converted into quaternary nanoparticles comprising AgInxGa1–xS2. Due to the well-controlled reaction steps, the product yield based on Ag was increased to 60%, which significantly exceeds that obtained using our previous approach of heating all-mixed raw materials (5–15%). After coating with gallium sulfide (GaSy) shells, the core/shell QDs exhibited an intense, green-colored band-edge emission with a tunable peak wavelength between 499 and 543 nm. The excellent uniformity of the core nanoparticles in terms of size and composition demonstrated a quite narrow band-edge emission with the full width at half maximum of 31 nm, which is equal to the record-narrow values of green-emitting cadmium-free QDs. Additionally, a near-unity photoluminescence quantum yield was achieved after postsynthetic surface treatment by alkylphosphines, indicating the defect-free nature of the prepared AgInxGa1–xS2/GaSy core/shell QD system.

Colossal Vacancy Effect of 2D CuInP2S6 Quantum Dots for Enhanced Broadband Photodetection

Band engineering is an effective way to tune the physical and chemical properties of materials, leading to significant performance improvement. Herein, the first two-dimensional (2D) quaternary quantum dots (QDs), CuInP2S6 (CIPS) QDs, were successfully fabricated by the lithium intercalation method with a high yield of ∼29%. Importantly, the tuned band structure of CIPS was achieved by forming colossal lithium-induced phosphorus and sulfur vacancies, endowing CIPS QDs with stronger and broader optical absorbance, as well as higher conductivity. Therefore, CIPS QDs exhibit outstanding intrinsic optoelectronic performances toward broadband photodetection with a broadband photoresponse from 405 to 1550 nm, a photoresponsivity of 22.9 A/W, a detectivity of 3.65 × 108 Jones, and a response speed of 60 ms. Especially, such excellent performances can be realized in a simple device structure and ambient air, exceptionally different from most 2D QD-based photodetectors requiring a heterostructure, gate voltage, or vacuum condition. In addition, CIPS QDs retain outstanding photoresponse on curving flexible substrates and in imaging applications. This work provides a unique venue for band structure tuning to effectively manipulate materials’ optoelectronic properties and functionalities.

Tuning the composition of heavy metal-free quaternary quantum dots for improved photoelectrochemical performance

The optical properties of heavy metal-free quaternary CuZnInS3 QDs can be optimized by tuning the composition, which is promising for improving the efficiency of QDs-PEC hydrogen generation.

Cu2BaSnS4 novel quaternary quantum dots for enhanced photocatalytic applications

Efficient photocatalysis in the visible light region for degradation of emerging contaminants grasped by quaternary Cu2BaSnS4 (CBTS) quantum dots. Structural, optical, and chemical studies are performed to appraise the physiochemical properties of CBTS. The optimized composition of CBTS with Ba = 0.6 reveals the bandgap of 2.6 eV. High absorption of photons in the visible region and small size made it capable of significant degradation of organic contaminants. The large surface area with sufficient reactive oxygen species disinfected large amounts of E. coli and S. aureus strains. Obtained results reveal that CBTS has excellent potential in photoelectrochemical, photovoltaic, and biological applications.

Rationally designed synthesis of bright AgInS2/ZnS quantum dots with emission control

In the blossoming field of Cd-free semiconductor quantum dots (QDs), ternary I-III-VI QDs have received increasing attention due to the ease of the environmentally friendly synthesis of high-quality materials in water, their high photoluminescence (PL) quantum yields (QYs) in the red and near infrared (NIR) region, and their inherently low toxicity. Moreover, their oxygen-insensitive long PL lifetimes of up to several hundreds of nanoseconds close a gap for applications exploiting the compound-specific parameter PL lifetime. To overcome the lack of reproducible synthetic methodologies and to enable a design-based control of their PL properties, we assessed and modelled the synthesis of high-quality MPA-capped AgInS2/ZnS (AIS/ZnS) QDs. Systematically refined parameters included reaction time, temperature, Ag:In ratio, S:In ratio, Zn:In ratio, MPA:In ratio, and pH using a design-of-experiment approach. Guidance for the optimization was provided by mathematical models developed for the application-relevant PL parameters, maximum PL wavelength, QY, and PL lifetime as well as the elemental composition in terms of Ag:In:Zn ratio. With these experimental data-based models, MPA:In and Ag:In ratios and pH values were identified as the most important synthesis parameters for PL control and an insight into the connection of these parameters could be gained. Subsequently, the experimental conditions to synthetize QDs with tunable emission and high QY were predicted. The excellent agreement between the predicted and experimentally found PL features confirmed the reliability of our methodology for the rational design of high quality AIS/ZnS QDs with defined PL features. This approach can be straightforwardly extended to other ternary and quaternary QDs and to doped QDs.

Biomimetic theranostic strategy for anti-metastasis therapy of breast cancer via the macrophage membrane camouflaged superparticles.

The rational design of theranostic systems are critical for addressing challenging issues associated with cancers. Toward this objective, the multifunctional biomimetic superparticle, termed as DOX-QDs-Lip@M, which can specifically deliver drug to tumor and synergistically monitor their therapeutic effects, was fabricated. Initially, anticancer drug doxorubicin hydrochloride (DOX) and imaging agent quaternary quantum dots (QDs) were loaded into the hydrophilic core region and hydrophobic chamber of liposome by self-assembly method, respectively. The integrated nanostructure can greatly increase the fluorescence intensity of signal unit and tremendously improve the diagnostic sensitivity. Subsequently, the biomimetic DOX-QDs-Lip@M was constructed by fusing and coating the isolated macrophage membranes on the surface of liposome, which can consequently extend the circulation of the whole blood and effectively target the tumor sites. Moreover, the naturally formed biofilm can stabilize the artificial liposome structure, which can prevent the leakage of the loaded materials in the liposome. These integrated properties endow the biomimetic DOX-QDs-Lip@M with improved tumor imaging and anti-metastasis treatment in living systems.

New Unsymmetrical Bisacridine Derivatives Noncovalently Attached to Quaternary Quantum Dots Improve Cancer Therapy by Enhancing Cytotoxicity toward Cancer Cells and Protecting Normal Cells.

The use of nanoparticles for the controlled drug delivery to cells has emerged as a good alternative to traditional systemic delivery. Quantum dots (QDs) offer potentially invaluable societal benefits such as drug targeting and in vivo biomedical imaging. In contrast, QDs may also pose risks to human health and the environment under certain conditions. Here, we demonstrated that a unique combination of nanocrystals core components (Ag-In-Zn-S) would eliminate the toxicity problem and increase their biomedical applications. The alloyed quaternary nanocrystals Ag-In-Zn-S (QDgreen, Ag1.0In1.2Zn5.6S9.4; QDred, Ag1.0In1.0Zn1.0S3.5) were used to transport new unsymmetrical bisacridine derivatives (UAs, C-2028 and C-2045) into lung H460 and colon HCT116 cancer cells for improving the cytotoxic and antitumor action of these compounds. UAs were coupled with QD through physical adsorption. The obtained results clearly indicate that the synthesized nanoconjugates exhibited higher cytotoxic activity than unbound compounds, especially toward lung H460 cancer cells. Importantly, unsymmetrical bisacridines noncovalently attached to QD strongly protect normal cells from the drug action. It is worth pointing out that QDgreen or QDred without UAs did not influence the growth of cancer and normal cells, which is consistent with in vivo results. In noncellular systems, at pH 5.5 and 4.0, which relates to the conditions of endosomes and lysosomes, the UAs were released from QD-UAs nanoconjugates. An increase of total lysosomes content was observed in H460 cells treated with QDs-UAs which can affect the release of the UAs from the conjugates. Moreover, confocal laser scanning microscopy analyses revealed that QD-UAs nanoconjugates enter H460 cells more efficiently than to HCT116 and normal cells, which may be the reason for their higher cytotoxicity against lung cancer. Summarizing, the noncovalent attachment of UAs to QDs increases the therapeutic efficiency of UAs by improving cytotoxicity toward lung H460 cancer cells and having protecting effects on normal cells.

EFFECT OF CYCLE COUNT IN SILAR DEPOSITION OF COUNTER ELECTRODE ON THE PERFORMANCE OF QUATERNARY QUANTUM DOT SENSITIZED SOLAR CELL

Cu-Ni-S alloyed films of different thicknesses were prepared by varying the number of cycles in SILAR deposition and were used for the application as Counter Electrode in QDSSCs. For device fabrication, titanium dioxide films were used as a photo-anode layer, Cu2ZnSnS4 quaternary quantum dots as a sensitizer, and polysulfide electrolyte was used as Redox mediator. The effect of number of SILAR cycles on the electrical and electrochemical parameters was studied with V-I characteristic curve and electrochemical impedance spectroscopy. The device incorporating counter electrode deposited by 10 SILAR cycles performed best among other devices because of its lowest impedance parameters.

Highly Efficient Zn-Cu-In-Se Quantum Dot-Sensitized Solar Cells through Surface Capping with Ascorbic Acid.

The balance between band structure, composition, and defect is essential for improving the optoelectronic properties of ternary and quaternary quantum dots and the corresponding photovoltaic performance. In this work, ascorbic acid (AA) as capping ligand is introduced into the reaction system to prepare green Zn-Cu-In-Se (ZCISe) quantum dots. Results show that the addition of AA can increase the Zn content while decrease the In content, resulting in enlarged band gap, high conduction band energy level, and suppressed charge recombination. When AA/Cu ratio is 1, the quantum dots possess the largest band gap of 1.49 eV and the assembled quantum dot-sensitized solar cells exhibit superior photovoltaic performance with ∼17% increment mainly contributed by the dramatically increased current density. The new record efficiencies of 10.44 and 13.85% are obtained from the ZCISe cells assembled with brass and titanium mesh-based counter electrodes, respectively.

Optical Properties, Synthesis, and Potential Applications of Cu-Based Ternary or Quaternary Anisotropic Quantum Dots, Polytypic Nanocrystals, and Core/Shell Heterostructures.

This review summaries the optical properties, recent progress in synthesis, and a range of applications of luminescent Cu-based ternary or quaternary quantum dots (QDs). We first present the unique optical properties of the Cu-based multicomponent QDs, regarding their emission mechanism, high photoluminescent quantum yields (PLQYs), size-dependent bandgap, composition-dependent bandgap, broad emission range, large Stokes’ shift, and long photoluminescent (PL) lifetimes. Huge progress has taken place in this area over the past years, via detailed experimenting and modelling, giving a much more complete understanding of these nanomaterials and enabling the means to control and therefore take full advantage of their important properties. We then fully explore the techniques to prepare the various types of Cu-based ternary or quaternary QDs (including anisotropic nanocrystals (NCs), polytypic NCs, and spherical, nanorod and tetrapod core/shell heterostructures) are introduced in subsequent sections. To date, various strategies have been employed to understand and control the QDs distinct and new morphologies, with the recent development of Cu-based nanorod and tetrapod structure synthesis highlighted. Next, we summarize a series of applications of these luminescent Cu-based anisotropic and core/shell heterostructures, covering luminescent solar concentrators (LSCs), bioimaging and light emitting diodes (LEDs). Finally, we provide perspectives on the overall current status, challenges, and future directions in this field. The confluence of advances in the synthesis, properties, and applications of these Cu-based QDs presents an important opportunity to a wide-range of fields and this piece gives the reader the knowledge to grasp these exciting developments.

A photoelectrochemical immunosensor based on gold nanoparticles/ZnAgInS quaternary quantum dots for the high-performance determination of hepatitis B virus surface antigen

ZnAgInS quaternary quantum dots were prepared using glutathione as the capped reagent. Gold nanoparticles (GNPs) were integrated with ZnAgInS QDs to provide a GNPs/ZnAgInS QDs nanocomposite. The morphological image, component and crystal structure of GNPs/ZnAgInS QDs were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A glassy carbon electrode surface was coated with GNPs/ZnAgInS QDs nanocomposites to construct an interface for immobilizing the antibody of hepatitis B virus surface antigen (anti-HBsAg). By employing GNPs/ZnAgInS QDs as a photoactive element, a photoelectrochemical immunosensor for hepatitis B virus surface antigen (HBsAg) was developed. The results indicate that gold nanoparticles can dramatically enhance the photocurrent response of ZnAgInS QDs and thus improving the sensing performances of the immunosensor. The experimental conditions including incubation time, incubation temperature, and ascorbic acid concentration were optimized. The relative photocurrent decline [Ri = ΔI/I0= (I0 − I)/I0] shows a linear relationship to the logarithm of HBsAg concentration [lg(c, ng mL−1)] in the range from 0.005 to 30 ng mL−1. A detection limit of 0.5 pg mL−1 was obtained. The immunosensor shows excellent sensitivity, selectivity, stability and reproducibility. The HBsAg concentrations in clinical serum samples were also accurately determined with this new photoelectrochemical immunosensor.

Facile preparation of yellow and red emitting ZnCdSeS quantum dots and their third-order nonlinear optical properties

In this study, N-acetyl-l-cysteine-capped quaternary ZnCdSeS quantum dots (QDs) were prepared using a colloidal method in two different structures, which we refer to as ZnCdSeS-yellow and ZnCdSeS-red QDs. These high quality QDs were synthesized directly in aqueous solution with two different amounts of the selenium precursor. The structural and optical properties of the ZnCdSeS QDs were studied to determine the compositions of the QDs and their composition-dependent absorption and emission characteristics. Regardless of the composition of the QDs, transmission electron microscopy measurements demonstrated that both quaternary QDs were similar in size with narrow size distributions. Using a continuous wave (CW) He-Ne laser at 632.8 nm, the linear absorption coefficients were calculated for each sample as approximately 7.55 × 101 and 8.99 × 101 m−1 for the ZnCdSeS-yellow and ZnCdSeS-red QDs, respectively. The magnitudes and signs of the third-order nonlinear refractive indices (n2) as well as the nonlinear absorption coefficients (β) were determined for the as-prepared QDs based on the closed and open aperture Z-scan at different intensities. The results indicated positive signs of n2 for both the ZnCdSeS QDs, thereby demonstrating the self-focusing effect in both QDs. The nonlinear susceptibility (χ(3)) values were also determined for the alloyed QDs. The n2, β, and χ(3) values for the QDs were in the orders of 10−12 m2 W−1, 10−4 mW−1, and 10−14 SI, respectively. Our results indicate that ZnCdSeS alloyed QDs are satisfactory candidate for use in nonlinear optical devices because of their intrinsic nonlinear and tunable emission properties.

One-pot synthesis of colloidal Cdx:CuInS2 quaternary quantum dots used as sensitizers in photovoltaic cells

Cdx:CuInS2 quaternary QDs were obtained in a one-pot reaction; these quaternary QDs exhibited enhanced photovoltaic performance compared to pristine CuInS2 ternary QDs.

Cu−In−Ga−S quantum dot composition-dependent device performance of electrically driven light-emitting diodes

Colloidal synthesis of ternary and quaternary quantum dots (QDs) of In/Ga ratio-varied Cu−In1−x−Gax−S (CIGS) with nominal x = 0, 0.5, 0.7, and 1 and their application for the fabrication of quantum dot-light-emitting diodes (QLEDs) are reported. Four QLEDs having CIGS QDs with different compositions are all solution-processed in the framework of multilayered structure, where QD emitting layer is sandwiched by hybrid charge transport layers of poly(9-vinlycarbazole) and ZnO nanoparticles. The device performance such as luminance and efficiency is found to be strongly dependent on the composition of CIGS QDs, and well interpreted by the device energy level diagram proposed through the determination of QD valence band minima by photoelectron emission spectroscopic measurement.