WS2 Quantum Dots Research Articles

The effect of laser energy on the size of WS2 quantum dots synthesized by pulsed laser ablation in liquid

The effect of laser energy on the size of WS2 quantum dots synthesized by pulsed laser ablation in liquid

Interfacial negative biexcitons in a monolayer WS2/InGaN quantum dots heterostructure

In this work, we fabricated a Van der Waals heterostructure of monolayer (ML) WS2 and InGaN quantum dots (QDs). This heterostructure is divided into coupled and uncoupled regions based on the thickness of the inserted hBN layer. Upon measuring its PL spectra, we identified an interfacial negative biexciton, which consists of a trion in ML WS2 and an exciton in QDs, in the coupled region. This interfacial negative biexciton features the negative charge of the trion and the quantum confinement of QDs, with its relative intensity showing a strong dependence on the excitation photon energy and featuring a significant threshold. Our work highlights the effective coupling within the mixed-dimensional heterostructure, offering new prospects for the study of many-body physics.

Enhanced upconversion luminescence of NaYF4:Er nanocrystals based on the synergy between whispering gallery mode excitation and förster resonant energy transfer

The upconversion luminescence at the visible band was excited by the high power density whispering gallery mode (WGM) on the surface of the microsphere. Under the WGM excitation, Er3+ of NaYF4:Er3+ directly absorbed three photons at 1525 nm, followed by the generation of upconversion luminescence. We used WS2 quantum dots (QDs) as donors and NaYF4:Er3+ upconversion nanoparticles (UCNPs) as acceptors to enhance upconversion luminescence by Förster resonant energy transfer (FRET). The physical mixture composed of monolayer WS2 and NaYF4:Er3+ nanoparticles was coated on SiO2 microsphere by immersion method. Excited by high power density WGM, three photons were absorbed by WS2-QDs based on the quantum size effect to generate excited electrons as donors and UCNPs as acceptors based on FRET, subsequently, the energy of the electrons were transferred to the luminescence center Er3+ to improve the upconversion luminescence efficiency. The mechanism model of upconversion luminescence enhancement based on FRET of WS2–NaYF4:Er3+ was proposed, and the enhancement effect was experimentally studied and demonstrated. To study the distance dependence of energy transfer between QD and UCNP pairs, we covered the surface of the silica microsphere with a controlled concentration of WS2 mixed with NaYF4:Er3+ nano-particles. When the mixed concentration of WS2-QDs was 0.15%, the upconversion luminescence reached the highest efficiency. The results showed that a twofold upconversion luminescence enhancement can be experimentally achieved. The proposed approach for enhancing the upconversion luminescence could benefit the improvement of imaging signal-to-noise ratio (SNR) using UCNPs for fluorescent labels in life sciences.

Blue-white electroluminescence of diamond/WS2 quantum dot composite films

Two kinds of diamond films with completely different morphologies were prepared on N-type heavily doped silicon wafers by microwave plasma chemical vapor deposition (MPCVD) method, namely, micron-scale large grain polycrystalline diamond film dominated by (220) crystal plane (220DF) and nano-scale small grain polycrystalline diamond film dominated by (111) crystal plane (111DF). And WS2 quantum dot powder was obtained by aqueous liquid phase ultrasonic method. Then, the 111DF/WS2 quantum dot composite structure film (111DWSF) and 220DF/WS2 quantum dot composite structure film (220DWSF) were prepared by applying WS2 quantum dot powder uniformly on diamond film substrate. The results of electroluminescence (EL) detection show that the 220DWSF device emits visible blue light, and the main peak of EL spectrum is located at 443 nm in the blue region. The 111DWSF device emits white light, and the corresponding EL spectra show strong emission peaks in the blue region (454 nm), green region (536 nm) and red region (632 nm) respectively, meanwhile, the luminous intensity of 111DWSF device is much higher than that of 220DWSF device. In addition, it is also found that the 220DWSF EL device does not show obvious rectification characteristics, while the 111DWSF EL device has obvious rectification characteristics. After FN fitting of the IV characteristic curve of 111DWSF EL device, the tunneling characteristics of electrons are found in the region of high electric field intensity.

Wrinkled Graphene Structure and Localized Surface Plasmon Resonance Induced Stretchable White Random Lasers Based on GLN‐functionalized 2D WS2 Quantum Dots

AbstractThis study presents investigations into the fabrication, characterization, and performance analysis of stretchable white random lasers based on 2D glutamine(GLN)‐functionalized WS2 quantum dots (QDs) enhanced by the integration of Au nanoparticles (NPs) and a wrinkled graphene structure. Wrinkled graphene holds the potential for achieving transient population inversion through electron collisions. Incorporating Au NPs introduces localized surface plasmon resonance (LSPR), which enhances the light‐matter interaction, resulting in reduced lasing thresholds. The GLN‐functionalized WS2 QDs exhibit strong photoluminescence emission, and their integration with a wrinkled graphene structure and Au NPs creates a synergistic effect that enhances the emission efficiency and enables the realization of white random lasing. The extensive characterization and analysis of the emission spectra under different deformation ratios provide valuable insights into the tunability and reliability of these devices, as well as the importance of light trapping due to the wrinkled graphene structure. The findings of this study underscore the significant potential of LSPR and wrinkled graphene structure induced stretchable and white random lasers based on 2D GLN‐functionalized WS2 QDs. These lasers may have a promising application in the field of flexible and wearable photonics, which is a critical step towards the development of next‐generation optoelectronic devices with improved performance.

Battery-type WS2 decorated WO3 nanorods for high-performance supercapacitors

Active sites enriched WS2 quantum dot decorated WO3 electrode was designed for supercapacitor application, using hydrothermal and sonication techniques. The WS2/WO3 electrode exhibited a specific capacitance of 570.1 F/g at 1 A/g due to numerous active sites, and facile electrolyte accessibility. The battery-type WS2/WO3//AC asymmetric supercapacitor device achieved an energy and power density of 55.6 Wh/kg and 1335 W/kg, and a notable retention capacitance and columbic efficiency of 87.4 % and 99.8 % for 5000 cycles at 6A/g, respectively. The results highlight WS2/WO3 as a promising electrode for supercapacitors.

Covalently linked graphene oxide-transition metal disulfide quantum dots nanocomposites featuring enhanced nonlinear optical absorption

Nanocomposites composed of different nanomaterials are a promising class of optoelectronic materials, owing to their interfacial electronic interactions. Compared to van der Waals forces, covalent bond-based linkages may endow nanocomposites with promoted electronic interactions and reinforced nonlinear optical (NLO) responses. In this study, we constructed covalently linked, mixed-dimensional nanocomposites by combining graphene oxide (GO) with MoS2 and WS2 quantum dots (QDs). These nanocomposites were prepared by employing a bifunctional molecule, 4-mercaptobenzenediazonium tetrafluoroborate, which carries a reactive diazonium group and a thiol group. The reactive diazonium group allowed for the attachment of thiophenol to GO via a radical addition reaction, while the thiol group enabled the subsequent passivation of sulfur vacancies in MoS2 and WS2 QDs. The resulting nanocomposites, denoted as GO-MoS2 and GO-WS2, respectively, exhibited significant fluorescence quenching, indicating effective electron and/or energy transfer from MoS2 or WS2 QDs to GO. Importantly, these covalently linked nanocomposites demonstrated superior two-photon absorption (TPA) responses compared to the individual components (GO, MoS2 and WS2 QDs) as well as the corresponding physical blends, presumably resulting from the efficient electron and/or energy transfer within these nanocomposites. This study not only demonstrates the significant promise of covalently linked GO-MoS2 and GO-WS2 nanocomposites in optical limiting applications, but also opens up new opportunities for the advancement of nanocomposites in ultrafast photonic devices.

In situ addition WS2 quantum dots on polymer films for white emission LED applications

This research focuses on the development of simple and low-cost white emission films for LED applications. Tungsten disulfide quantum dots (WS2 QDs) were synthesized using a simple hydrothermal approach and then studied physio-chemical properties. Morphological investigation revealed that the QDs were 3.7 nm in size. The QDs were incorporated into a Polyvinyl Alcohol (PVA) film, yielding stacked films that emitted white light. The stacked film had a color rendering index of 76 % and CIE coordinates of (0.35, 0.34). Through the entrapment of WS2 QDs within PVA films, this study proposes a feasible strategy for lab-scale development of white emission LEDs.

First-Principles Study of MoS2, WS2, and NbS2 Quantum Dots: Electronic Properties and Hydrogen Evolution Reaction

The electronic and catalytic properties of two-dimensional MoS2, WS2, and NbS2 quantum dots are investigated using density functional theory investigations. The stability of the considered structures is confirmed by the positive binding energies and the real vibrational frequencies in the infrared spectra. The ab initio molecular dynamics simulations show that these nanodots are thermally stable at 300 K with negligible changes in the potential energy and metal–S bonds. The pristine nanodots are semiconductors with energy gaps ranging from 2.6 to 3 eV. Edge sulfuration significantly decreases the energy gap of MoS2 and WS2 to 1.85 and 0.75 eV, respectively. The decrease is a result of the evolution of low-energy molecular orbitals by the passivating S-atoms. The energy gap of NbS2 is not affected, which could be due to the spin doublet state. Molecular electrostatic potentials reveal that the edge sulfur/transition metal atoms are electrophilic/nucleophilic sites, while the surface atoms are almost neutral sites. MoS2 quantum dots show an interestingly low change in the hydrogen adsorption free energy ~0.007 eV, which makes them competitive for hydrogen evolution catalysts.

One-Step Synthesis of Transition Metal Dichalcogenide Quantum Dots Using Only Alcohol Solvents for Indoor-Light Photocatalytic Antibacterial Activity.

In this study, we report a one-step direct synthesis of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) quantum dots (QDs) through a solvothermal reaction using only alcohol solvents and efficient Escherichia coli (E. coli) decompositions as photocatalytic antibacterial agents under visible light irradiation. The solvothermal reaction gives the scission of molybdenum-sulfur (Mo-S) and tungsten-sulfur (W-S) bonding during the synthesis of MoS2 and WS2 QDs. Using only alcohol solvent does not require a residue purification process necessary for metal intercalation. As the number of the CH3 groups of alcohol solvents among ethyl, isopropyl, and tert(t)-butyl alcohols increases, the dispersibility of MoS2/WS2 increases. The CH3 groups of alcohols minimize the surface energy, leading to the effective exfoliation and disintegration of the bulk under heat and pressure. The bulky t-butyl alcohol with the highest number of methyl groups shows the highest exfoliation and yield. MoS2 QDs with a lateral size of about 2.5 nm and WS2 QDs of about 10 nm are prepared, exhibiting a strong blue luminescence under 365 nm ultraviolet (UV) light irradiation. Their heights are 0.68-3 and 0.72-5 nm, corresponding to a few layers of MoS2 and WS2, respectively. They offer a highly efficient performance in sterilizing E. coli as the visible-light-driven photocatalyst.

Magnetic and Electronic Properties of Edge-Modified Triangular WS2 and MoS2 Quantum Dots

The magnetic and electronic properties of zigzag-triangular WS2 and MoS2 quantum dots are investigated using density functional theory calculations. The pristine WS2 and MoS2 nanodots hold permanent spin on their edges which originates from the unpaired electrons of the transition metals at the edges. The ferromagnetic spin ordering in zigzag-triangular WS2 and MoS2 can be transformed to antiferromagnetic ordering with S = 0 and to nonmagnetic, respectively, by edge passivation with 2H. The calculations of the Curie Temperature indicate that these magnetic states are stable and withstand room temperature. The paramagnetic susceptibility of these structures significantly decreases by edge sulfuration. Moreover, it can be converted to diamagnetic susceptibility by edge passivation with 2H as found in WS2 nanodots. These structures are semiconductors with energy gaps of ~3.3 eV that decrease unexpectedly by edge passivation due to the existence of lone pairs from S atoms that give a high contribution to the low-energy molecular orbitals. With these preferable magnetic properties and controlled electronic ones, WS2 and MoS2 quantum dots are potential candidates for spintronic applications.

WS2 quantum dots modified In2O3 hollow hexagonal prisms for conductometric NO2 sensing at room-temperature

The fabrication and investigations of a novel NO2 gas sensor based on a 1T and 2H mixed phase WS2 quantum dots (QDs) modified MOF-derived hollow In2O3 (WS2 QDs@In2O3) heterostructure were documented. The proposed gas sensor based on WS2 QDs@In2O3 hollow hexagonal prisms was simple, sensitive, cost-effective and worked at room temperature (25 ± 2 °C). The response value of 3 wt% WS2 QDs@In2O3 (W3In) towards 100 ppm NO2 could reach to 2034, which was an ultra-high value and almost 7.7 times higher than that of pure In2O3. Besides, our sensor showed excellent selectivity to NO2 and could detect concentration down to 100 ppb. The enhanced NO2 sensing performance was observed due to the synergistic effect between WS2 and In2O3. Furthermore, the compensation response values to NO2 based on the response to water vapor under different humidity of W3In were calculated and their fluctuations are within 7.8 % compared with the response under 25 % RH, which could provide a new strategy for accurately detecting NO2.

Fast detection of Staphylococcus aureus using thiol-functionalized WS2 quantum dots and Bi2O2Se nanosheets hybrid through a fluorescence recovery mechanism.

Ultrafast and sensitive detection of Staphylococcus aureus (S. aureus), a harmful Gram-positive human pathogenic bacterium, by two-dimensional layered materials continues to be a challenge. Herein, we have studied the sensing of S. aureus using a tungsten disulfide (WS2) quantum dot (QD) and bismuth oxyselenide (Bi2O2Se) nanosheet (NS) hybrid through their unique optical functionalities. The WS2 QDs of a mean diameter of 2.5 nm were synthesized by liquid exfoliation. Due to the quantum confinement and functional groups, the WS2 QDs exhibit high fluorescence (FL) yield under UV excitation. The addition of Bi2O2Se NSs resulted in the adsorption of WS2 QDs on their surface, resulting in quenching of the FL emission due to nonfluorescent complex formation between the WS2 QDs and Bi2O2Se NSs. A specific sequencing single-standard DNA (ssDNA) aptamer, which identifies and explicitly binds with S. aureus, was attached to the defect sites of the WS2 QDs for selective detection. The thiol-modified ssDNA aptamers attach covalently to the WS2 QD defect sites, which was confirmed by Raman and X-ray photoelectron spectroscopy (XPS). The interaction of S. aureus with the aptamer functionalized WS2 QDs weakens the van der Waals interaction between the WS2 QDs and Bi2O2Se NSs, which results in the detachment of the WS2 QDs from the Bi2O2Se NS surface and restores the FL intensity of the WS2 QDs, thus allowing the efficient detection of S. aureus. Similar measurements with non-targeted bacteria show that the system is quite selective towards S. aureus. Our FL-based biosensor has a linear response in the range of 103-107 CFU mL-1 (colony formation unit mL-1) with a detection limit of 580 CFU mL-1. We have observed a fast response time of 15 minutes for sensing, which is superior to the previous reports. The proposed system was tested in human urine and can detect S. aureus in human urine samples selectively, proving its potential in real-life applications. The reported approach is versatile enough for sensing other biomolecules and metal ions by choosing suitable receptors.

Synthesis of biologically important tetrahydroisoquinoline (THIQ) motifs using quantum dot photocatalyst and evaluation of their anti-bacterial activity.

Our study introduces an efficient photocatalytic approach for synthesizing biologically significant C1-substituted tetrahydroisoquinoline (THIQ) motifs, employing WS2 quantum dots (QDs) as catalysts. This method enables the formation of C-C and C-P bonds at the C1 position of the THIQ motif. The resulting compounds exhibit substantial antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacteria, with low minimum inhibitory concentration (MIC) values. Notably, the WS2 QD catalyst demonstrates recyclability and suitability for gram-scale reactions, underscoring the sustainability and scalability of our approach. Overall, our research presents a versatile and cost-effective strategy for synthesizing C1-substituted THIQ derivatives, highlighting their potential as novel therapeutic agents in biology and medicinal chemistry.

Correction: WS2 quantum dots harvesting via sonication assisted liquid exfoliation for the electrochemical sensing of xanthine

Correction for ‘WS2 quantum dots harvesting via sonication assisted liquid exfoliation for the electrochemical sensing of xanthine’ by Arunkumar Sakthivel et al., New J. Chem., 2022, 46, 17066–17072, https://doi.org/10.1039/D2NJ03446H.

Sulfur vacancy defects healing of WS2 quantum dots boosted hole extraction for all-inorganic perovskite solar cells

The promotion of interfacial charge transfer and extraction plays an important role in further improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, a composite of WS2/AgIn5S8 quantum dots (QDs) with lattice matching and suitable energy level is launched as an efficient hole extractor for carbon-based all-inorganic CsPbBr3 PSCs. Due to the sulfur vacancy defects passivation of WS2 QDs by AgIn5S8 QDs and a Type-II band alignment between them, a boosted hole extraction and transfer is realized. In addition, the strong interaction of S of WS2/AgIn5S8 QDs and the Pb of perovskite film constructs a convenient pathway of hole transport to promote hole transfer and heals the surface lead ions defects of perovskite film, and the uncoordinated bromine ions defects of CsPbBr3 film are also passivated by the WS2/AgIn5S8 QDs in the form of Ag-Br and In-Br bonds, leading to an inhibition of charge recombination. As a result, the carbon-based all-inorganic CsPbBr3 PSCs with WS2/AgIn5S8 QDs free of encapsulation deliver a maximum PCE of 10.24 % and a remarkably improved stability with over 93 % retention of the initial efficiency after being stored in air with high humidity and temperature (85 % RH, 85 °C) for 720 h.

Defect-mediated carrier dynamics and third-order nonlinear optical response of WS2 quantum dots.

In this Letter, we report the third-order absorptive and refractive nonlinear optical response of highly luminescent WS2 quantum dots (QDs) in the off-resonant femtosecond and nanosecond pulses, which is beneficial for optical limiting and quantum information processing. For 800 nm femtosecond excitation, QDs show two-photon absorption (β = (107 ± 2)×10-3 cm/GW) with positive nonlinearity originating from bound carriers. This picture changes significantly for 532 nm nanosecond excitation, where it shows reverse saturable absorption with negative nonlinearity primarily originating from the sequential absorption of two single photons through the shallow defects, creating free carriers. Our results provide a promising route toward low-dimensional optoelectronic devices.

Concatenated DNA Circuit-Assembled DNAzyme as an Amplified Quencher for MicroRNA Detection

In this study, we designed a fluorimetric assay for ultrasensitive determination of microRNA-141 based on WS2 quantum dots (WS2 QDs) and concatenated DNA circuit-assembled DNAzymes. WS2 QDs are synthesized using sodium tungstate and cysteine as W and S sources, and the use of biomass materials as a precursor is environment-friendly. The presence of microRNA-141 can trigger the CHA and HCR, leading to the formation of long dsDNA nanochains with numerous HRP-mimicking DNAzymes. The o-phenylenediamine structure was oxidized to 2,3-diaminophenazine by the DNAzymes. WS2 QDs could be quenched by 2,3-diaminophenazine via the inner filter effect. This method is highly sensitive for the analysis of microRNA-141 with a limit of detection of 2.7 fM. The designed strategy has no measurable response to four other microRNAs. The WS2 QDs-based sensor was used for the microRNA-141 assay in human serum and microRNA-141 expression in MDA-MB-231 cells. This newly developed biosensor shows great potential for the analysis of biomarkers and early diagnosis of microRNA-related diseases.

A novel probe for tetracyclines detection and its applications in cell imaging based on fluorescent WS2 quantum dots

In this study, a novel fluorescence sensor for tetracyclines (TCs) detection was designed using WS2 quantum dots (WS2 QDs). WS2 QDs could be quenched by TCs through the inner filter effect (IFE). The limit of detection of this proprosed method is 39 nM, 52 nM, and 28 nM for tetracycline (TC), doxycycline (DC), and oxytetracycline (OTC), respectively. The as-proposed strategy was successfully applied to detect TC in milk samples and human serum samples. The WS2 QDs were highly biocompatible and showed lower toxicity. Moreover, the WS2 QDs was successfully applied to imaging TC in HeLa cells owing to its excellent optical performance and great biocompatibility.

High-Responsivity Gate-Tunable Ultraviolet-Visible Broadband Phototransistor Based on Graphene-WS2 Mixed-Dimensional (2D-0D) Heterostructure.

Recent progress in the synthesis of highly stable, eco-friendly, cost-effective transition-metal dichalcogenide (TMDC) quantum dots (QDs) with their broadband absorption spectra and wavelength selectivity features have led to their increasing use in broadband photodetectors. With the solution-based processing, we demonstrate a superlarge (∼0.75 mm2), ultraviolet-visible (UV-vis) broadband (365-633 nm) phototransistor made of WS2 QDs-decorated chemical vapor deposited (CVD) graphene as the active channel with extraordinary stability and durability under ambient conditions (without any degradation of photocurrent until 4 months after fabrication). Here, colloidal zero-dimensional (0D) WS2 QDs are used as the photoabsorbing material, and graphene acts as the conducting channel. A high photoresponsivity (3.1 × 102 A/W), moderately high detectivity (∼8.9 × 108 Jones), and low noise equivalent power (∼9.7 × 10-11 W/Hz0.5) are obtained at a low bias voltage (Vds = 1 V) at an illumination of 365 nm with optical power as low as ∼0.8 μW/cm2, which can be further tuned by modulating the gate bias. While comparing the photocurrent between two different morphologies of WS2 [QDs and two-dimensional (2D) nanosheets], a significant enhancement of photocurrent is observed in the case of QD-based devices. Ab initio density functional theory (DFT)-based calculations further support our observation, revealing the role of quantum confinement in enhanced photoresponse. Our work reveals a strategy toward developing a scalable, cost-effective, high-performance hybrid mixed-dimensional (2D-0D) photodetector with graphene-WS2 QDs for next-generation optoelectronic applications.