Te Quantum Dots Research Articles

An innovative chalcogenide transfer agent for improved aqueous quantum dot synthesis.

An innovative approach to chalcogenide precursor synthesis and their subsequent use for the production of CdX (X = S, Se, Te) quantum dots (QDs) in water under scalable and intensified continuous flow conditions is introduced. Herein, tris(2-carboxyethyl)phosphine (TCEP) is identified as a novel, efficient and water-soluble vehicle for chalcogenide transfer to form CdX QDs under aqueous conditions. A comprehensive exploration of critical process parameters, including pH, chalcogen excess, and residence time, utilizing a Design of Experiments (DoE) approach is reported. Reaction kinetics are investigated in real-time using a combination of in situ Raman spectroscopy and in-line 31P NMR spectroscopy. The conversion of TCEP into TCEP[double bond, length as m-dash]X (X = S, Se, Te) species is seamlessly adapted to continuous flow conditions. TCEP[double bond, length as m-dash]X precursors are subsequently employed in the synthesis of CdX QDs. Scalability trials are successfully demonstrated, with experiments conducted at flow rates of up to 80 mL min-1 using a commercially available mesofluidic flow reactor with favorable metrics. Furthermore, biocompatible and aqueous CdSe/ZnS core-shell QDs are for the first time prepared in flow within a fully concatenated process. These results emphasize the potential for widespread biological or industrial applications of this novel protocol.

Heavy-metal-free blue-emitting ZnSe(Te) quantum dots: synthesis and light-emitting applications

Synthesis and improvement strategies of blue ZnSe(Te)-based QDs are reviewed and discussed. Recent advances regarding blue ZnSe(Te)-based light-emitting applications are systematically outlined, and existing challenges and prospects are provided.

Investigation on nonlinear optical and optical limiting properties of Cd0.7Zn0.3Te quantum dots

Ternary alloyed Cd0.7Zn0.3Te colloidal quantum dots were synthesized under open atmosphere conditions. The Cd0.7Zn0.3Te quantum dots were characterized under XRD studies, DLS technique and optical absorption measurements. Using tauc and urbach relation the optical energy bandgap and urbach energy were obtained. The intensity depended nonlinear optical parameters of Cd0.7Zn0.3Te quantum dots were determined with Z-scan experimental setup using a green laser source working on continuous wave mode. The nonlinear absorption coefficient β, along with optical limiting capacity of Cd0.7Zn0.3Te quantum dot is investigated through the open aperture set up. The transmittance of Cd0.7Zn0.3Te quantum dot showed a sharp dip at the maximum intensity point of the laser which indicates reverse saturable absorption. The optical limiting threshold value for Cd0.7Zn0.3Te quantum dot was obtained around 4.6 KJ/cm2. The nonlinear refractive index of Cd0.7Zn0.3Te quantum dot is find out using closed aperture set up. The nonlinear refractive index with a negative sign was obtained for the Cd0.7Zn0.3Te quantum dot which is attributed to the self-defocusing phenomena. The nonlinear studies indicate that the sample exhibits good nonlinear properties and find applications in optical limiting materials.

Excitonic fine structure of epitaxial Cd(Se,Te) on ZnTe type-II quantum dots

The structure of the ground-state exciton of Cd(Se,Te) quantum dots embedded in ZnTe matrix is studied experimentally using photoluminescence spectroscopy and theoretically using $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ and configuration interaction methods. The experiments reveal a considerable reduction of fine-structure splitting energy of the exciton with an increase of Se content in the dots. That effect is interpreted by theoretical calculations to originate due to the transition from spatially direct (type-I) to indirect (type-II) transition between electrons and holes in the dot induced by an increase of Se. The trends predicted by the theory match those of the experimental results very well. The theory identifies that the main mechanism causing elevated fine-structure energy, in particular in type-I dots, is due to the multipole expansion of the exchange interaction. Moreover, the theory reveals that for Se contents in the dot $>0.3$, there also exists a peculiar type of confinement showing signatures of both type I and type II and which exhibits extraordinary properties, such as an almost purely light hole character of exciton and toroidal shapes of hole states.

Bandgap engineering of ZnX (X = O, S, Se, Te) QDs/Graphene nanocomposites: Towards the designing of a highly efficient light-harvesting device

Increasing the power conversion efficiency (PCE) of photovoltaic devices (PVDs) is a topic of fundamental importance not only for academia but also for industry. In this study, we systematically investigated the electronic structure of ZnX (X = O, S, Se, and Te) quantum dots (QDs)/Graphene (G) nanohybrid systems by employing the density functional method. To understand the key issues, associated with photoinduced charge generation, generated charge separation, charge transfer process, recombination probability, and variations of PCE, we have considered different combinations of hybrid nanostructures composed with ZnX QD and G. The tuning of the electronic properties of hybrid systems has been done as a function of the size of ZnX QD's, chalcogenides, and hydrogen coverage percentage on G to design a highly efficient hybrid solar cell. We have also explored the photovoltaic efficiency of ZnX/ZnX’ (X/X' = O, S, Se, and Te) core/shell QDs/G to investigate the effect of core/shell QDs in composite nanomaterials. Bandgaps of ZnX QDs/G nanocomposites are very low (0.028eV–0.158 eV) which implies the probability of recombination of photo-induced separated charges at the heterojunction region is very high. After passivation with hydrogen atoms partially on the G, this unsavory circumstance is overcome. We have performed the bandgap and band alignment engineering of ZnX QDs/G hybrid nanostructures by varying the size of QD's and H-coverage percentage on G to form a type-II material which is very important to reduce the recombination rate and ultimately increase the PCE of the hybrid solar cells. Considering hydrogenated graphene (HG)-ZnX QDs nanocomposites we were achieving high PCE values (up to 30.25%), which implies our explored materials efficiency is exceptionally good and competitive with recently explored tandem/hybrid/latest perovskite solar cells.

Thiolate Etching Route for the Ripening of Uniform Ag2Te Quantum Dots Emitting in the Second Near-Infrared Window: Implication for Noninvasive In Vivo Imaging

Thiolate Etching Route for the Ripening of Uniform Ag₂Te Quantum Dots Emitting in the Second Near-Infrared Window: Implication for Noninvasive <i>In Vivo</i> Imaging

Thiolate-Assisted Route for Constructing Chalcogen Quantum Dots with Photoinduced Fluorescence Enhancement.

Despite great efforts in the development of diverse nanomaterials, a general route to synthesize metal-free chalcogen quantum dots (QDs) is still lacking. Moreover, the modification of chalcogen QDs is a bottleneck that severely hinders their applications. Herein, we develop a facile method to construct different chalcogen QDs (including S QDs, Se QDs, and Te QDs) with the assistance of thiolates. In addition to stabilizing chalcogen QDs, the thiolates also endow the chalcogen QDs with favorable modifiability. Different from most dyes whose fluorescence is quenched after short-term light irradiation, the prepared chalcogen QDs have significantly enhanced fluorescence emission under continuous light irradiation. Taking advantage of the distinctive photoinduced fluorescence enhancement property, long-time cell imaging with superb performance is realized using the chalcogen QDs. It is envisioned that the chalcogen QDs show promising potential as fluorescent materials in different fields beyond bioimaging.

Water-Soluble High-Quality Ag2Te Quantum Dots Prepared by Mutual Adaptation of Synthesis and Surface Modification for In Vivo Imaging.

Near-infrared (NIR) in vivo fluorescence imaging has exhibited the distinct advantage of high optical resolution at deeper penetration into biological tissues. Ag2Te quantum dots (QDs), with a relatively narrow band gap, show great promise for fluorescence emission at long wavelengths in the second near-infrared (NIR-II) window for bioimaging. However, existing Ag2Te QDs have severely hindered the application of in vivo bioimaging due to their poor fluorescence brightness and stability, so it is important to prepare Ag2Te QDs with high quantum yield and stability as well as high biocompatibility in the NIR-II window. Herein, we designed an integrated method for the preparation of water-soluble Ag2Te QDs by mutual adaptation of QD synthesis and surface modification. We first synthesized high-quality Ag2Te QDs with different NIR-II emission wavelengths and the photoluminescence quantum yields (PLQYs) up to 6.51% by rapidly injecting the TBP-Te precursor into a hot solvent to form a highly fluorescent Ag2Te core. Then water-dispersible Ag2Te QDs were obtained by direct exchange of the hydrophobic Ag2Te QD surface ligands with thiol ligands. The PLQY of the water-soluble Ag2Te QDs obtained by this method can still be maintained at 4.94%. With these highly bright and stable Ag2Te QDs, the abdominal vessels, hindlimb arterial vessels, venous vessels, sacral lymph nodes, and tumor vessels were visualized non-invasively in vivo in the NIR-II window in mice. The results demonstrate that the integrated strategy of QD synthesis and modification provides valuable technical support for further in-depth applications of Ag2Te QDs.

Au-Doped Ag2 Te Quantum Dots with Bright NIR-IIb Fluorescence for In Situ Monitoring of Angiogenesis and Arteriogenesis in a Hindlimb Ischemic Model.

Fluorescence located in 1500-1700nm (denoted as the near-infrared IIb window, NIR-IIb) has drawn great interest for bioimaging, owing to its ultrahigh tissue penetration depth and spatiotemporal resolution. Therefore, NIR-IIb fluorescent probes with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. Herein, a novel NIR-IIb fluorescent probe of Au-doped Ag2 Te (Au:Ag2 Te) quantum dots (QDs) is developed via a facile cation exchange method. The Au dopant concentration in the Ag2 Te QDs is tunable from 0% to 10% by controlling the ratio of supplied Au precursor to Ag2 Te QDs, resulting in a wide range of PL emission in the NIR-IIb window and a much-enhanced PL intensity. After surface modification, the Au:Ag2 Te QDs possess bright NIR-IIb emission, high colloidal stability and photostability, and decent biocompatibility. Further, in vivo monitoring of the process of angiogenesis and arteriogenesis in an ischemic hindlimb is successfully performed.

Temperature- and size-dependent photoluminescence in colloidal CdTe and Cd x Zn1−x Te quantum dots

Semiconductor colloidal quantum dots (QDs) of CdTe and alloyed Cd x Zn1−x Te QDs with N-acetyl-L-cysteine capping ligands are synthesized by a reflux method in aqueous solution. Alloying provides a new degree of freedom to tune the optical and electronic properties of the nanocrystals. The photoluminescence (PL) of Cd x Zn1−x Te QDs is sharper and displays a highly enhanced quantum yield (QY) of 65% relative to the 16% of CdTe QDs. The fluorescence of Cd x Zn1−x Te QDs is observed to be highly stable for over 12 months without degradation, while that of CdTe QDs begins to mildly flocculate around 8 months of storage. To characterise the material structure and composition, UV-Vis absorption spectroscopy, x-ray powder diffraction, transmission electron microscopy, and inductively coupled plasma mass spectrometry measurements are carried out. To understand the fundamental processes that play in the luminescence behaviour, temperature- and size-dependent PL spectra are investigated in the range 80–300 K. The Varshni and O’Donnell equations fit well on the PL peak emission energies and the Huang–Rhys parameter indicates the strengthening of exciton–phonon coupling in the nanocrystals upon alloying and with decreasing nanocrystal sizes. PL linewidth analysis reveals that the inhomogeneous broadening is considerably reduced in Cd x Zn1−x Te QDs relative to CdTe. Moreover, the quantum confinement effect of the nanocrystals leads to an increase in exciton–acoustic phonon interactions with the coefficients ranging between 26.9 and 95.6 µeV K−1 compared to the bulk CdTe value of 0.72 µeV K−1. Exciton–longitudinal optical phonon interactions are made stronger by the ZnTe alloying with the coefficients lying in the range between 24.8 and 41.7 meV and also with the effect of increasing crystal size. An Arrhenius plot of PL integrated area is used to calculate the thermal activation energy value E a of the non-radiative recombination channel, which is 132 meV for CdTe QDs and a higher value of 185 meV for Cd x Zn1−x Te QDs. This is consistent with the observed QY enhancement in Cd x Zn1−x Te QDs as a higher E a value indicates reduced generation of non-radiative recombination centres and a decrease in defect densities upon alloying. Cd x Zn1−x Te QDs with enhanced fluorescence properties serve both as a medium for studying fundamental effects of alloying and its properties, and for practical applications such as biomedical labelling and optoelectronics.

Optical signatures of type I–type II band alignment transition in Cd(Se,Te)/ZnTe self-assembled quantum dots

Self-assembled Cd(Se,Te) quantum dots with various Se compositions embedded in the ZnTe matrix are grown by molecular beam epitaxy. A huge redshift of the near band edge emission, from 2.1 eV to 1.5 eV, with an increasing Se content in the dots is observed. It is accompanied by an increase in the excitonic lifetime by the factor of 10. We associate these effects with a gradual change from the direct type I confinement character in CdTe/ZnTe quantum dots to the staggered type II band alignment in the case of Cd(Se,Te)/ZnTe dots. This interpretation is consistent with the micro-photoluminescence study of several individual quantum dots, which reveals a gradual decrease in the biexciton–exciton energy difference with the increasing content of Se in the dots, which leads ultimately to the change from the binding to antibinding character of biexcitons. The latter effect originates, most likely, from the increasing Coulomb repulsion between excitons forming dipoles at the dot/barrier interface.

Ag2Te Quantum Dots as Contrast Agents for Near-Infrared Fluorescence and Computed Tomography Imaging

Multifunctional nanoparticles hold great potential for clinical and medical research. Herein, Ag2Te QDs were applied as multifunctional contrast agents for the second near-infrared region (NIR-II) fluorescence and X-ray computed tomography (CT) imaging. In vitro and in vivo experiments demonstrated that Ag2Te QDs exhibited low toxicity and remarkable fluorescence and CT imaging contrast properties. Moreover, long-term fluorescence imaging was also achieved. These results indicated that Ag2Te QDs had great potential as multifunctional contrast agents for near-infrared fluorescence and CT imaging in clinical research.

Highly Efficient Inorganic–Organic Heterojunction Solar Cells Based on Polymer and CdX (X = Se, Te) Quantum Dots: An Insight from a Theoretical Study

By using the density functional method, we explore the potentiality of recently synthesized CdX (X=Se, Te)QD/P3HT composites in solar energy conversion devices. Our study reveals that inorganic/org...

Controlled Synthesis of Ag2 Te@Ag2 S Core-Shell Quantum Dots with Enhanced and Tunable Fluorescence in the Second Near-Infrared Window.

Fluorescence in the second near-infrared window (NIR-II, 900-1700 nm) has drawn great interest for bioimaging, owing to its high tissue penetration depth and high spatiotemporal resolution. NIR-II fluorophores with high photoluminescence quantum yield (PLQY) and stability along with high biocompatibility are urgently pursued. In this work, a Ag-rich Ag2 Te quantum dots (QDs) surface with sulfur source is successfully engineered to prepare a larger bandgap of Ag2 S shell to passivate the Ag2 Te core via a facile colloidal route, which greatly enhances the PLQY of Ag2 Te QDs and significantly improves the stability of Ag2 Te QDs. This strategy works well with different sized core Ag2 Te QDs so that the NIR-II PL can be tuned in a wide range. In vivo imaging using the as-prepared Ag2 Te@Ag2 S QDs presents much higher spatial resolution images of organs and vascular structures as compared with the same dose of Ag2 Te nanoprobes administrated, suggesting the success of the core-shell synthetic strategy and the potential biomedical applications of core-shell NIR-II nanoprobes.

Cell Membrane-Camouflaged NIR II Fluorescent Ag2 Te Quantum Dots-Based Nanobioprobes for Enhanced In Vivo Homotypic Tumor Imaging.

The advantages of fluorescence bioimaging in the second near-infrared (NIR II, 1000-1700 nm) window are well known; however, current NIR II fluorescent probes for in vivo tumor imaging still have many shortcomings, such as low fluorescence efficiency, unstable performance under in vivo environments, and inefficient enrichment at tumor sites. In this study, Ag2 Te quantum dots (QDs) that emit light at a wavelength of 1300 nm are assembled with poly(lactic-co-glycolic acid) and further encapsulated within cancer cell membranes to overcome the shortcomings mentioned above. The as-prepared ≈100 nm biomimetic nanobioprobes exhibit ultrabright (≈60 times greater than that of free Ag2 Te QDs) and highly stable (≈97% maintenance after laser radiation for 1 h) fluorescence in the NIR II window. By combining the active homotypic tumor targeting capability derived from the source cell membrane with the passive enhanced permeation and retention effect, improved accumulation at tumor sites ((31 ± 2)% injection dose per gram of tumor) and a high tumor-to-normal tissue ratio (13.3 ± 0.7) are achieved. In summary, a new biomimetic NIR II fluorescent nanobioprobe with ultrabright and stable fluorescence, homotypic targeting and good biocompatibility for enhanced in vivo tumor imaging is developed in this study.

Tuning Ternary Zn1-xCdxTe Quantum Dot Composition: Engineering Electronic States for Light-Activated Superoxide Generation as a Therapeutic against Multidrug-Resistant Bacteria.

Quantum-confined states of semiconductor nanocrystals offer unique opportunities for selective light-activated photochemistry and generation of specific reactive oxygen (ROS) and nitrogen (RNS) species. Recently, assessment of different ROS and RNS species identified intracellular light-activated superoxide as the prime candidate for selective nanotherapeutic treatments in countering the threat of multidrug-resistant (MDR) pathogens. Here, we show that by carefully tuning the composition of ternary zinc cadmium telluride (Zn1-xCdxTe) quantum dots (QDs), we can engineer the bandgap, electronic states, and the resultant reduction and oxidation potentials, thereby changing the light-activated superoxide generation by these QDs. Using QDs with low cadmium content as alternative candidates for selective light-activated therapy, we show negligible toxicity of these QDs to mammalian cells while maintaining high treatment efficacy against MDR pathogens. These low nanomolar doses of QDs required for therapeutic intervention contain less cadmium than other environmental factors like consuming tubular potatoes, leafy vegetables, animal meat, or even fresh water, further alleviating concerns of elemental toxicity. These results provide design principles for developing different QDs as selective therapeutics to counter the growing threat of antimicrobial-resistant infections.

Interface modification in type-II ZnCdSe/Zn(Cd)Te QDs for high efficiency intermediate band solar cells

A new growth process for type-II ZnCdSe/ZnCdTe quantum dots (QDs) is developed to avoid formation of a deleterious strain-inducing ZnSe interfacial layer (IL) that forms during the migration enhanced epitaxy growth process used to form the QDs. This new growth sequence allows for improved control of the interfacial composition and simplifies the fabrication of the intermediate band solar cell device structure based on these QDs, since additional strain balancing schemes are no longer required to grow stress-free structures. In contrast to previous results, lattice-matched QD superlattices were obtained using near lattice-matched ZnCdSe barrier layers. X-ray diffraction and excitation intensity dependent photoluminescence studies were used to support such a conclusion. Our findings have applications for the growth of other heterointerfaces in which an undesirable IL may form due to lack of a common anion, and to desorption and incorporation of competing elements.

One-step Synthesis and Enhanced Thermoelectric Properties of Polymer-Quantum Dot Composite Films.

Conventional syntheses of polymer-inorganic composite thermoelectric materials suffer major problems such as inhomogeneity, large particle size, and oxidation that result in ineffective loading. Now a one-step synthesis can be used to fabricate high-quality small-sized anions codoped poly(3,4-ethylenedioxythiophene):dodecylbenzenesulfonate/Cl-tellurium (PEDOT:DBSA/Cl-Te) composite films using a series of novel TeIV -based oxidants. The synchronized production of PEDOT and Te results in thick and homogeneous films containing evenly distributed and well-protected Te quantum dots. Owing to the heavily doped crystalline polymer matrix as well as the <5 nm unoxidized Te quantum dot loading, at low Te concentrations as 2.1-5.8 wt %, the films exhibits high power factors of about 100 μW m-1 K-2 , which is 50 % higher compared to a pure PEDOT:DBSA film.

One‐step Synthesis and Enhanced Thermoelectric Properties of Polymer–Quantum Dot Composite Films

AbstractConventional syntheses of polymer–inorganic composite thermoelectric materials suffer major problems such as inhomogeneity, large particle size, and oxidation that result in ineffective loading. Now a one‐step synthesis can be used to fabricate high‐quality small‐sized anions codoped poly(3,4‐ethylenedioxythiophene):dodecylbenzenesulfonate/Cl‐tellurium (PEDOT:DBSA/Cl‐Te) composite films using a series of novel TeIV‐based oxidants. The synchronized production of PEDOT and Te results in thick and homogeneous films containing evenly distributed and well‐protected Te quantum dots. Owing to the heavily doped crystalline polymer matrix as well as the &lt;5 nm unoxidized Te quantum dot loading, at low Te concentrations as 2.1–5.8 wt %, the films exhibits high power factors of about 100 μW m−1 K−2, which is 50 % higher compared to a pure PEDOT:DBSA film.

Наногетероструктуры с квантовыми точками CdTe/ZnMgSeTe для однофотонных источников, формируемые методом молекулярно-пучковой эпитаксии

AbstractData on the molecular beam epitaxy (MBE) technology, design, and luminescent properties of heterostructures with CdTe/Zn(Mg)(Se)Te quantum dots on InAs(001) substrates are presented. X-ray diffraction has been used to study short-period ZnTe/MgTe/MgSe superlattices used as wide-bandgap barriers in structures with CdTe/ZnTe quantum dots for the effective confinement of holes. It is shown that the design of these superlattices must take into account the replacement of Te atoms by selenium on MgSe/ZnTe and MgTe/MgSe heterointerfaces. Heterostructures with CdTe/Zn(Mg)(Se)Te quantum dots exhibit photoluminescence at temperatures up to 300 K. The spectra of microphotoluminescence at T = 10 K display a set of emission lines from separate CdTe/ZnTe quantum dots, the surface density of which is estimated at ~10^10 cm^−2.