Ultrasmall Quantum Dots Research Articles

FeNi2S4 QDs @C composites as a high capacity and long life anode material for lithium ion battery and ex situ investigation of electrochemical mechanism

Nowadays, exploiting electrode materials with high energy density and long cycling life is crucial for meeting the urgent requirement of ever-growing energy storage for EV/HEV. Herein, we introduced a simple synthetic route to prepare FeNi2S4 QDs @C composites on a large scale. By means of suitable design, the ultra-small FeNi2S4 quantum dots (QDs) were encapsulated in the carbon matrix, and the forming FeNi2S4 QDs @C composites exhibit excellent electrochemical performances. When tested as anode materials for lithium ion battery, the high capacity of 920 mAhg−1 at 0.1 Ag-1 could be achieved. Except the high capacity, the FeNi2S4 QDs @C composites present the enhancing cycling stability, which demonstrated more than 700 cycles with twice capacity of graphite and capacity retention of almost 100% could be achieved, compared to the capacity of second cycle. Detailed investigations of phase evolutions by XRD patterns and TEM indicate the phase segregation of FeSx and NiSy during the charge/discharge process. The conversion reactions between Fe/Ni and FeSx/NiSy took place in the carbon matrixes, which would hinder the aggregation and grow-up of nanoparticles, resulting in the structure stability. Hence, the ultra-small size, self-doping and stable structure led to the superior electrochemical properties. We believe that the FeNi2S4 @C composites would be an alternative anode material for next generation lithium ion battery.

Nanomedicine for cancer diagnosis and therapy: advancement, success and structure-activity relationship.

Multifunctional nanoparticles (NPs), composed of organic and inorganic materials, have been explored as promising drug-delivery vehicles for cancer diagnosis and therapy. The success of nanosystems has been attributed to its smaller size, biocompatibility, selective tumor accumulation and reduced toxicity. The relationship among numbers of molecules in payload, NP diameter and encapsulation efficacy have crucial role in clinical translation. Advancement of bioengineering, and systematic fine-tuning of functional components to NPs have diversified their optical and theranostic properties. In this review, we summarize wide varieties of NPs, such as ultrasmall polymer-lipid hybrid NPs, dendrimers, liposomes, quantum dots, carbon nanotubes, gold NPs and iron oxide NPs. We also discuss their tumor targetability, tissue penetration, pharmacokinetics, and therapeutic and diagnostic properties. [Formula: see text].

Black Phosphorus: Synthesis and Application for Solar Cells

AbstractFew‐layer ultrathin nanosheets and ultrasmall quantum dots of black phosphorus (BP) have attracted increasing research interest due to their fascinating properties including a tunable bandgap, high carrier mobility, and ambipolar conduction ability. These excellent properties together with their unique structures make BP derivatives promising candidates for a wide range of device applications. In this research news, the latest advancements in the synthesis, properties, and applications of BP and its derivatives are highlighted. In particular, the focus is on the use of these rising star materials for emerging solar cells, in terms of both theoretical predictions and experimental investigations. Finally, the authors' personal perspectives on potential future research directions are provided.

MoS2 quantum dots interspersed WO3 nanoplatelet arrays with enhanced photoelectrochemical activity

Facing the issues for ineffective visible light utilization, insufficient separation of photogenerated electron-hole pairs of WO3 photoanode, herein, ultrasmall MoS2 quantum dots (QDs) are exploited as surface sensitizers to boost the photoelectrochemical (PEC) properties of MoS2/WO3. The MoS2/WO3 photoanode is prepared by decorating 2D WO3 nanoplatelet arrays with ultra-small MoS2 QDs via a facile and effective assembly method. The interspersing of MoS2 QDs, not only broadens the photoabsorption region, but also provides more active sites for the surface reactions and enhances charge separation of the photogenerated electron-hole pairs, leading to a 2.13-fold enhancement in photocurrent density at 1.0V vs. Ag/AgCl (1.23V vs. RHE). MoS2/WO3 photoanodes hold potentialities for the straightforward building of molecular level devices for PEC production.

Improving the emission of ultrasmall Mn-doped ZnInS quantum dots via Ag-induced trap state energy level

For ultrasmall Mn-doped quantum dots (QDs), the energy transfer of the exciton to the Mn is the key factor for Mn emission. Herein, the Ag-induced electron trap state energy level, which is an intermediate energy level between the conduction band (CB) and 4T1 of Mn, is proposed for improving the energy transfer. After doping the Ag and forming Ag&Mn:ZnInS QDs, most excitons will first be captured by the intermediate energy level and then be transferred to Mn d-states, leading to enhanced photoluminescence (PL) quantum yields (QY) of the QDs from the original 17% (Mn:ZnInS QDs) to 30% (Ag&Mn:ZnInS QDs).

In situ synthesis of ultrasmall SnO2 quantum dots on nitrogen-doped reduced graphene oxide composite as high performance anode material for lithium-ion batteries

SnO2 is considered as one of the anode material for Li-ion batteries in terms of its superiority in high theoretical capacity (1494 mAh g−1), low cost and environmental friendly. However, it is suffered from several issues such as rapid capacity deterioration, undesirable aggregation of tin particles and pesky expansion of volume. To conquer these shortcomings, a novel composite of ultrasmall SnO2 quantum dots with an average particle size of 4–5 nm anchored on nitrogen-doped reduced graphene oxide (SnO2@NRGO) was first in situ synthesized By means of hydrothermal method. The results show that as-prepared SnO2@NRGO electrode exhibits a greater enhancement in its initial discharge capacity (1678.4 mAh g−1) and reversible capacity (1333.5 mAh g−1 after 450 cycles) at a current density of 500 mA g−1, implying a long cycle life. Furthermore, the high rate capability of SnO2@NRGO is superior to SnO2@RGO and SnO2 electrodes. The excellent electrochemical reversibility of SnO2@NRGO electrode can be ascribed to the great conductivity, ultrahigh specific surface area and the synergetic effect between ultrasmall SnO2 quantum dots and NRGO.

Radioprotective effect of ultra-small carbon quantum dots in mice in vivo

Objective To study the radioprotective effects of ultra-small carbon quantum dots (CQDs) in mice in vivo, and to reveal the protective mechanism, as well as to study the body immune response to CQDs and the toxicity in vivo. Methods Mice were injected with different concentrations of CQDs solution. Mice models of systemic radiation injury were constructed by high dose gamma rays radiation. The 30-days survival rate, bone marrow DNA, femoral bone marrow nucleated cells (BMNC), tissue superoxide dismutase (SOD) and malondialdehyde (MDA) were measured to evaluate the radioprotective effects of CQDs, and to investigate the possible protective mechanism. The toxicity of CQDs in vivo was studied by measuring the changes of body weight, liver index and spleen index before and after injections of CQDs in mice. Results CQDs showed obvious radioprotective effects on mice in vivo. Compared with the control group, the 30-days survival rate of irradiated mice treated with CQDs increased from 0% to 40%. CQDs could effectively reduce the hematopoietic system damages caused by radiation, and increase the level of bone marrow DNA, femur BMNC, liver and lung SOD, as well as reduce the production of MDA in liver and lung. The results of immunological reaction tests showed that CQDs had less toxicity in vivo and did not trigger the body immune response. Conclusions CQDs has tremendous application prospects in the field of radiation protection. This study can provide new ideas for the application of new nano-materials in medical field. Key words: Carbon quantum dots; Radiation protection; In vivo toxicity

Broadband ultrafast nonlinear absorption and ultra-long exciton relaxation time of black phosphorus quantum dots.

Black phosphorus (BP) has recently attracted significant attention for its brilliant physical and chemical features. The remarkable strong light-matter interaction and tunable direct wide range band-gap make it an ideal candidate in various application regions, especially saturable absorbers. In this paper, ultrasmall black phosphorus quantum dots (BPQDs), a unique form of phosphorus nanostructures, with average size of 5.7 ± 0.8 nm are synthesized. Compared with BP nanosheets (BPNs) with similar thickness, the ultrafast nonlinear optical (NLO) absorption properties and excited carrier dynamics are investigated in wide spectra. Beyond the saturation absorption (SA), giant two photon absorption (TPA) is observed in BPQDs. BPQDs exhibit quite different excitation intensity and wavelength dependent nonlinear optical (NLO) response from BPNs, which is attributed to the quantum confinement and edge effects. The BPQDs show broadband photon-induced absorption (PIA) under the probe wavelength from 470 nm to 850 nm and a fast and a slow decay time are obtained as long as 92 ± 10 ps and 1100 ± 100 ps, respectively. The substantial independence for ultra-long time scales of pump intensity and temperature reveals that the carrier recombination mechanism may be attributed to a defect-assisted Auger capture process. These findings will help to develop optoelectronic and photonic devices operating in the infrared and visible wavelength region.

Tunable Broadband Nonlinear Optical Properties of Black Phosphorus Quantum Dots for Femtosecond Laser Pulses.

Broadband nonlinear optical properties from 500 to 1550 nm of ultrasmall black phosphorus quantum dots (BPQDs) have been extensively investigated by using the open-aperture Z-scan technique. Our results show that BPQDs exhibit significant nonlinear absorption in the visible range, but saturable absorption in the near-infrared range under femtosecond excitation. The calculated nonlinear absorption coefficients were found to be (7.49 ± 0.23) × 10−3, (1.68 ± 0.078) × 10−3 and (0.81 ± 0.03) × 10−3 cm/GW for 500, 700 and 900 nm, respectively. Femtosecond pump-probe measurements performed on BPQDs revealed that two-photon absorption is responsible for the observed nonlinear absorption. The saturable absorption behaviors observed at 1050, 1350 and 1550 nm are due to ground-state bleaching induced by photo-excitation. Our results suggest that BPQDs have great potential in applications as broadband optical limiters in the visible range or saturable absorbers in the near-infrared range for ultrafast laser pulses. These ultrasmall BPQDs are potentially useful as broadband optical elements in ultrafast photonics devices.

Phosphorene quantum dot saturable absorbers for ultrafast fiber lasers

We fabricate ultrasmall phosphorene quantum dots (PQDs) with an average size of 2.6 ± 0.9 nm using a liquid exfoliation method involving ultrasound probe sonication followed by bath sonication. By coupling the as-prepared PQDs with microfiber evanescent light field, the PQD-based saturable absorber (SA) device exhibits ultrafast nonlinear saturable absorption property, with an optical modulation depth of 8.1% at the telecommunication band. With the integration of the all-fiber PQD-based SA, a continuous-wave passively mode-locked erbium-doped (Er-doped) laser cavity delivers stable, self-starting pulses with a pulse duration of 0.88 ps and at the cavity repetition rate of 5.47 MHz. Our results contribute to the growing body of work studying the nonlinear optical properties of ultrasmall PQDs that present new opportunities of this two-dimensional (2D) nanomaterial for future ultrafast photonic technologies.

Ultrasmall Quantum Dots: A Tool for in Vitro and in Vivo Fluorescence Imaging

Fluorescence bioimaging is an increasingly popular approach in biomedical research and diagnosis, where semiconductor nanocrystals or quantum dots (QDs) have proved to be excellent fluorescent labels. The use of ultrasmall QDs in nanoprobes extends the possibilities of bioimaging owing to an enhanced capacity for penetrating through cell membranes. However, the QDs synthesis is accompanied by the rapid growth of nanocrystals in colloidal medium what prevents obtaining sufficiently small QDs prepared by conventional approaches. Here, a one-pot injection technique of QD synthesis in an organic medium, with the reaction terminated at an early crystal growth stage and excess precursors eliminated by gel permeation chromatography, is proposed. This technique yields defect-free cadmium selenide QD cores about 1.5 nm in size emitting at the wavelengths less than 500 nm. Coating of these QDs with epitaxial shells of different compositions ensures a photoluminescence quantum yield approaching 100%. The resultant ultrasmall QDs are promising components of nanoprobes to be used for imaging intracellular and intranuclear events down to the molecular level.

Ultraviolet saturable absorption and ultrafast carrier dynamics in ultrasmall black phosphorus quantum dots.

Understanding the photoexcited carrier-relaxation actions in ultrasmall black phosphorus quantum dots (BPQDs) will play a crucial role in the fields of electronics and optoelectronics. Herein, we report the ultraviolet (UV) saturable absorption and ultrafast photoexcited carrier-relaxation dynamics of BPQDs. The ultrasmall BPQDs are synthesized using a facile liquid-exfoliation method and possess a diameter of 3.8 ± 0.6 nm and a thickness of 1.5 ± 0.4 nm. Femtosecond open-aperture (OA) Z-scan measurements showed typical saturable absorption properties in the UV band. A negative nonlinear optical (NLO) absorption coefficient of -(1.4 ± 0.3) × 10-3 cm GW-1 and a saturable intensity of 6.6 ± 1.3 GW cm-2 were determined. Using a degenerate pump-probe technique, an ultrafast photoexcited carrier-recombination time was observed in the range of 216-305 fs, which was 3 orders of magnitude faster than that of BP nanosheets. Such an ultrafast relaxation component may be attributable to the edge- and step-mediated recombination and was confirmed by our density functional theory (DFT) calculations. This work provides fundamental insight into the underlying mechanism of the photoexcited carrier relaxation dynamic action in BPQDs which can enable UV photonic devices.

Ultrasmall PbS quantum dots: a facile and greener synthetic route and their high performance in luminescent solar concentrators

Tributylphosphine-assisted greener synthesis of ultrasmall PbS quantum dots and their high performance in luminescent solar concentrator application.

Ultrasmall quantum dots for fluorescent bioimaging in vivo and in vitro

Photoluminescent semiconductor quantum dots (QDs) are widely used in many branches of diagnostics and biomedicine. Using ultrasmall QDs for designing fluorescent nanoprobes increases their capacity for penetrating through cell membranes, which allows one to use them for tracking intracellular processes at the molecular level. Obtaining small-size QDs is usually impeded due to the fast kinetics of reactions of their formation and growth in a colloidal medium. We propose a method of synthesizing defectless CdSe QDs with a diameter of 1.5 nm based on the injection reaction in an organic medium, with superfast termination of the growth of QDs at the early stage of their formation. Separation of QDs by means of gel-permeation chromatography allows one to completely remove the excess of cadmium precursors not entering the reaction, which ensures the subsequent obtaining of QDs with a controllable fluorescence wavelength and high quantum yield in the process of depositing protective epitaxial shells of different compositions. The obtained ultrasmall QDs may find application in developing photoluminescent nanoprobes for visualizing intranuclear processes in cells.

Ultra-small vanadium nitride quantum dots embedded in porous carbon as high performance electrode materials for capacitive energy storage

Abstract Ultra-small vanadium nitride quantum dots embedded in porous carbon (VNQDs/PC) were fabricated by a thermal treatment process of NH 4 VO 3 /C 3 H 6 N 6 under nitrogen atmosphere. The specific capacitance of VNQDs/PC was 1008 mF cm −2 at a current density of 0.004 A cm −2 , whereas the VN/carbon hybrid material obtained by a solid-state blending of NH 4 VO 3 and C 3 H 6 N 6 just exhibited a capacitance of 432 mF cm −2 at the same current density. By mediating the ratio of NH 4 VO 3 and C 3 H 6 N 6 , a maximum specific capacitance of 1124 mF cm −2 was achieved at a current density of 0.002 A cm −2 in aqueous 6 mol/L KOH electrolyte with the potential range from 0 to −1.15 V when it reached 1: 7 (wt./wt.). Additionally, symmetrical supercapacitor fabricated with synthesized VNQDs/PC presented a high specific capacitance of 215 mF cm −2 at 0.002 A cm −2 based on the entire cell, and exhibited a high capacitance retention of 86.6% with current density increased to 5 A g −1 . The VNQDs/PC negative electrodes were combined with Ni(OH) 2 positive electrodes for the fabrication of hybrid supercapacitors. Remarkably, at a power density of 828.7 W kg −1 , the device delivered an ultrahigh energy density of 47.2 Wh kg −1 .

Study on the blocking effect of a quantum-dot TiO2 compact layer in dye-sensitized solar cells with ionic liquid electrolyte under low-intensity illumination

In this study, ultrasmall and ultrafine TiO2 quantum dots (QDs) were prepared and used as a high-performance compact layer (CL) in dye-sensitized solar cells (DSCs). We systematically investigated the performance of TiO2 CL under both low-intensity light and indoor fluorescent light illumination and found that the efficiency of DSCs with the insertion of optimal TiO2 QDs-CL was increased up to 18.3% under indoor T5 fluorescent light illumination (7000 lux). We clarified the controversy over the blocking effect of TiO2 CL for the efficiency increment and confirmed that the TiO2 QDs-CL performed significantly better under low-intensity illumination due to the efficient suppression of electron recombination at the FTO/electrolyte interface. We, for the first time, demonstrate this potential for the application of the DSCs with TiO2 QDs-CL in the low-intensity light and indoor fluorescent light illumination.

MoS2‐Quantum‐Dot‐Interspersed Li4Ti5O12 Nanosheets with Enhanced Performance for Li‐ and Na‐Ion Batteries

Rational nanoscale surface engineering of electroactive nanoarchitecture is highly desirable, since it can both secure high surface‐controlled energy storage and sustain the structural integrity for long‐time and high‐rate cycling. Herein, ultrasmall MoS2 quantum dots (QDs) are exploited as surface sensitizers to boost the electrochemical properties of Li4Ti5O12 (LTO). The LTO/MoS2 composite is prepared by anchoring 2D LTO nanosheets with ultrasmall MoS2 QDs using a simple and effective assembly technique. Impressively, such 0D/2D heterostructure composites possess enhanced surface‐controlled Li/Na storage behavior. This unprecedented Li/Na storage process provides a LTO/MoS2 composite with outstanding Li/Na storage properties, such as high capacity and high‐rate capability as well as long‐term cycling stability. As anodes in Li‐ion batteries, the materials have a stable specific capacity of 170 mAhg−1 after 20 cycles and are able to retain 94.1% of this capacity after 1000 cycles, i.e., 160 mAhg−1, at a high rate of 10 C. Due to these impressice performance, the presented 0D/2D heterostructure has great potential in high‐performance LIBs and sodium‐ion batteries.

Ultrasmall Magnetically Engineered Ag2Se Quantum Dots for Instant Efficient Labeling and Whole-Body High-Resolution Multimodal Real-Time Tracking of Cell-Derived Microvesicles.

Cell-derived microvesicles (MVs) are natural carriers that can transport biological molecules between cells, which are expected to be promising delivery vehicles for therapeutic purposes. Strategies to label MVs are very important for investigation and application of MVs. Herein, ultrasmall Mn-magnetofunctionalized Ag2Se quantum dots (Ag2Se@Mn QDs) integrated with excellent near-infrared (NIR) fluorescence and magnetic resonance (MR) imaging capabilities have been developed for instant efficient labeling of MVs for their in vivo high-resolution dual-mode tracking. The Ag2Se@Mn QDs were fabricated by controlling the reaction of Mn(2+) with the Ag2Se nanocrystals having been pretreated in 80 °C NaOH solution, with an ultrasmall size of ca. 1.8 nm, water dispersibility, high NIR fluorescence quantum yield of 13.2%, and high longitudinal relaxivity of 12.87 mM(-1) s(-1) (almost four times that of the commercial contrast agent Gd-DTPA). The ultrasmall size of the Ag2Se@Mn QDs enables them to be directly and efficiently loaded into MVs by electroporation, instantly and reliably conferring both NIR fluorescence and MR traceability on MVs. Our method for labeling MVs of different origins is universal and free of unfavorable influence on intrinsic behaviors of MVs. The complementary imaging capabilities of the Ag2Se@Mn QDs have made the long-term noninvasive whole-body high-resolution dual-mode tracking of MVs in vivo realized, by which the dynamic biodistribution of MVs has been revealed in a real-time and in situ quantitative manner. This work not only opens a new window for labeling with QDs, but also facilitates greatly the investigation and application of MVs.

Towards understanding the unusual photoluminescence intensity variation of ultrasmall colloidal PbS quantum dots with the formation of a thin CdS shell.

In this study, we report anomalous size-dependent photoluminescence (PL) intensity variation of PbS quantum dots (QDs) with the formation of a thin CdS shell via a microwave-assisted cation exchange approach. Thin shell formation has been established as an effective strategy for increasing the PL of QDs. Nonetheless, herein we observed an unusual PL decrease in ultrasmall QDs upon shell formation. We attempted to understand this abnormal phenomenon from the perspective of trap density variation and the probability of electrons and holes reaching surface defects. To this end, the quantum yield (QY) and PL lifetime (on the ns-μs time scales) of pristine PbS QDs and PbS/CdS core/shell QDs were measured and the radiative and non-radiative recombination rates were derived and compared. Moreover, transient absorption (TA) analysis (on the fs-ns time scale) was performed to better understand exciton dynamics at early times that lead to and affect longer time dynamics and optical properties such as PL. These experimental results, in conjunction with theoretical calculations of electron and hole wave functions, provide a complete picture of the photophysics governing the core/shell system. A model was proposed to explain the size-dependent optical and dynamic properties observed.

Fabrication and multifunctional properties of ultrasmall water-soluble tungsten oxide quantum dots.

A facile and green method has been demonstrated to synthesize ultrasmall tungsten oxide quantum dots (WOx QDs). The water-soluble WOx QDs present high luminescence stability, strong peroxidase-like activity, and excellent electrochemiluminescence properties. This work provides an eco-friendly strategy to prepare multifunctional WOx QDs, and opens the door for bioapplications of the WOx QDs.