Aggregation Of Quantum Dots Research Articles

High performance pixelated quantum dots array on Micro-LED by inkjet printing

Micro-LED display has risen to prominence in research and industry, distinguished by their numerous advantages. Quantum dots (QDs) film, serving as color conversion layers (CCLs) for Micro-LED, are considered a leading candidate for the next generation of displays, owing to their low power consumption and broad color gamut. Inkjet printing stands out as a feasible approach for crafting QDs CCLs. The essence of the process hinges on attaining a printed QDs film that boasts both uniformity and high-precision QDs array. However, the unstable printing of QDs ink significantly impacts the surface morphology of QDs arrays and the display performance of Micro-LEDs. Therefore, elucidating the mechanism behind the unstable printing of QDs in inkjet printing and fabricating QDs is of paramount importance. In this study, through the simulation of unstable printing with conventional QDs ink, we identified nozzle blockage and the rapid evaporation of low-boiling-point ink as the primary causes of unstable printing. This leads to aggregation and deposition of QDs, obstructing the nozzle and altering the fluid path. A novel binary organic composite ink was employed to print the QDs array on the substrate with ultra-stability, achieving a high yield and greatly reduced coffee-ring effect Micro-LED full-color display.

Effect of InP/ZnS quantum dots aggregation on the kinetics of birefringence recorded in thin azopolymer composite films

The article describes the preparation of new thin film composite materials based on the azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with three different concentration of InP/ZnS quantum dots with size of 7.5 nm. Clusters of aggregated InP/ZnS were microscopically observed in the fabricated composite samples. Birefringence (Δn) was induced in the films at two different wavelengths of the pump laser (355 nm and 444 nm) and the obtained higher values of Δnmax for the samples doped with quantum dots up to 2 wt% in comparison to the non-doped film and the sample with the highest nanocrystals concentration are discussed, based on the measured fluorescence spectra, in terms of possible local energy transfer between the azobenzene chromophores and the InP/ZnS quantum dots.

(Invited) Electrochemistry of CdSe Quantum Dots in Organic Solvents. from Stochastic Electrochemistry to Film Behavior

We present our electrochemistry results of CdSe quantum dots in two organic solvents: neat methanol and acetonitrile. In MeOH, the quantum dots (QDs) can be detected through stochastic collisions; that is, as agglomerates of QDs collide with an electrode surface, the photocurrent changes as a result of the CdSe entities that collide with the electrode surface.1 The experiment presented here uses Pt ultramicroelectrodes (UME), that is, electrodes with a diameter of 25 μm or less. Our results show that the CdSe can accumulate on the surface of the electrode, and the technique provides a high degree of control. By controlling the time the electrode collects QDs, one can control the amount of CdSe that accumulates at the electrode surface. After collecting CdSe on the surface, we perform cyclic voltammetry experiments to confirm that the electrode surface has changed. In acetonitrile (MeCN), we can perform CVs over large potential windows to study the electrochemistry of the deposited CdSe. The electrochemical response of the deposited CdSe resembles that of a film, although the surface has sub-monolayer coverages, as will be discussed from the images of scanning electron microscopy (SEM).Figure 1 shows an example of a LSV in a region of interest where the current due to the CdSe significantly deviates from the background current. The LSV was run in the dark, so the current in the figure is a function of the density of states in the CdSe structures. It is also a function of the reversibility of the CV, i.e., mainly of the scan rate of the experiment. After the CV experiments, the Pt UME can be imaged in the SEM to correlate the electrochemical results with the CdSe deposited on the electrode surface. We will discuss our findings in terms of the results in the literature on CdSe electrochemistry (e.g., refs 2-5). References. (1) Subedi, P.; Parajuli, S.; Alpuche-Aviles, M. A., "Single Entity Behavior of CdSe Quantum Dot Aggregates During Photoelectrochemical Detection", Frontiers in Chemistry 9 (2021) DOI: 10.3389/fchem.2021.733642(2) Kohl, P. A.; Bard, A. J., "Semiconductor electrodes. 13. Characterization and behavior of n-type zinc oxide, cadmium sulfide, and gallium phosphide electrodes in acetonitrile solutions", Journal of the American Chemical Society 99, 7531-7539 (1977) DOI: 10.1021/ja00465a023(3) Hines, M. A.; Guyot-Sionnest, P., "Synthesis and characterization of strongly luminescing ZnS-capped CdSe nanocrystals", The Journal of Physical Chemistry 100, 468-471 (1996) DOI: 10.1021/jp9530562(4) Zhang, J. Z., "Interfacial Charge Carrier Dynamics of Colloidal Semiconductor Nanoparticles", The Journal of Physical Chemistry B 104, 7239-7253 (2000) DOI: 10.1021/jp000594s(5) Myung, N.; Ding, Z.; Bard, A. J., "Electrogenerated chemiluminescence of CdSe nanocrystals", Nano Letters 2, 1315-1319 (2002) Figure 1

Effect of Crystal Structure on the Aggregation of CdS Quantum Dots: Consequences for Photophysical Properties and Photocatalytic Hydrogen Evolution Activity

Effect of Crystal Structure on the Aggregation of CdS Quantum Dots: Consequences for Photophysical Properties and Photocatalytic Hydrogen Evolution Activity

Lead sulfide quantum dot-linear low-density polyethylene composites for near-infrared Mini-LEDs

Lead sulfide quantum dots (QDs), presenting near-infrared (NIR) emissions, have gained extensive interest within the realm of NIR light-emitting diodes (LEDs). However, the intricate surface defect passivation poses a major impediment that curbs broader applications of PbS QDs. To address it, we introduce linear low-density polyethylene (LLDPE) as a facilitating agent for the aggregation of PbS QDs, aiming to improve their optical properties by harnessing a stress-inducing effect. Compared to the bare PbS QDs that are luminescence silent, the PbS aggregates formed with the addition of LLDPE show a notable photoluminescence quantum yield (PLQY) as high as 20.7 %. Moreover, the presence of LLDPE mitigates the oxidative degradation of lead ions on the PbS QD surface, thereby enhancing the stability of the PbS QDs through steric hindrance. Near-infrared nini-LEDs are demonstrated by combining the PbS QD/LLDPE composites with blue mini-LED chips, which show an emission maximum of 1517.9 nm, a full width at half maximum (FWHM) of 297.6 nm and an energy conversion efficiency (ECE) of 14.6 %. The proposed method opens up new avenues for enhancing the optical properties of PbS QDs without using traditional passivation procedures.

Aggregation-Enabled Electrochemistry in Confined Nanopore Capable of Complementary Faradaic and Non-Faradaic Detection.

Electrochemistry that empowers innovative nanoscopic analysis has long been pursued. Here, the concept of aggregation-enabled electrochemistry (AEE) in a confined nanopore is proposed and devised by reactive oxygen species (ROS)-responsive aggregation of CdS quantum dots (QDs) within a functional nanopipette. Complementary Faradaic and non-Faradaic operations of the CdS QDs aggregate could be conducted to simultaneously induce the signal-on of the photocurrents and the signal-off of the ionic signals. Such a rationale permits the cross-checking of the mutually corroborated signals and thus delivers more reliable results for single-cell ROS analysis. Combined with the rich biomatter-light interplay, the concept of AEE can be extended to other stimuli-responsive aggregations for electrochemical innovations.

P-n heterogeneous Sb2S3/SnO2 quantum dot anchored reduced graphene oxide nanosheets for high-performance lithium-ion batteries.

Antimony sulfide (Sb2S3) has a high theoretical specific capacity due to its two reaction mechanisms of conversion and alloying during the Li+-(de)intercalation process, thus becoming a promising lithium-ion battery (LIB) anode material. However, its poor inherent conductivity and large volume expansion during repeated Li+-(de)intercalation processes greatly hinder the in-depth development of Sb2S3 based LIB anode materials. Herein, an Sb2S3/SnO2@rGO composite was prepared by using an interface engineering technique involving metal-containing ionic liquid precursors, in which Sb2S3/SnO2 quantum dots (QDs) as p-n heterojunctions are uniformly anchored on the surface of reduced graphene oxide (rGO). The p-n heterogeneous interface between Sb2S3 and SnO2 QDs induces an internal electric field, promoting the electronic/ion transport during electrochemical reactions, and the QD-sized Sb2S3/SnO2 heterostructure with a larger surface area provides more active sites for Li+-(de)intercalation reactions. In addition, the rGO matrix acts as a buffer to prevent the aggregation of active Sb2S3 and SnO2 QDs, alleviate the volume expansion, and enhance the conductivity of the composite during repeated cycles. These advantages endow the designed Sb2S3/SnO2@rGO electrode with excellent reaction kinetics and good long cycling stability. As an anode material of LIBs, it can still provide a reversible specific capacity of 474 mA h g-1 after 2000 cycles at a high current density of 3.0 A g-1, which is superior to those of most of the previously reported Sb2S3-based carbon materials. The p-n heterostructure construction strategy of nano-metal sulfide/metal oxides in this work can provide inspiration for the design and synthesis of other advanced energy storage materials.

Ionic liquid alkyl chain regulated highly stable and luminescent silica-coated perovskite quantum dots for bright white light-emitting diodes

Silica-coated perovskite quantum dots (QDs), which exhibit exceptional photophysical properties, hold great promise for various optoelectronic applications. Nonetheless, the issue of insufficient stability poses a significant challenge to their continued advancement and widespread adoption. Herein, we present a novel approach for the synthesis of silica-coated CH3NH3PbBr3 (CH3NH3 = MA) QDs with exceptional stability and luminescence, which utilized hydrophobic ionic liquids (ILs) with unlike alkyl chain lengths as surface ligands. As the alkyl chain length of the hydrophobic ILs increased, we observed a blue-shift in the wavelength and a reduction in the time required to reach maximum fluorescence for the silica-coated perovskite QDs. It not only effectively prevents QD aggregation but also accelerates the formation rate of the SiO2 shell. The introduction of ILs generated the enhancement of photoluminescence quantum yield (PLQY) from 85% for the pristine sample to 92.83% for ILs treated C16-QDs@SiO2. Furthermore, the stability of the ILs-treated C16-QDs@SiO2 was notably enhanced, with the fluorescence intensity retaining 80.5% after 40 days of storage. The as-prepared white light emitting diode (LED) displayed a high color rendering index (CRI) of 75.3 and a correlated color temperature (CCT) of 7529 K. This work provides an alternative strategy to solve the challenging stability issue of silica-coated perovskite QDs and promote the silica-coated perovskite QDs to the practical application in solid-state LEDs.

Structural engineering of SnS quantum dots embedded in N, S Co-Doped carbon fiber network for ultrafast and ultrastable sodium/potassium-ion storage

Tin sulfides have received significant attention as potential candidates for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to their abundance, high theoretical capacity, and favorable working potential. However, the inherent drawbacks such as slow kinetics, low intrinsic electronic conductivity, and significant volume change during cycling, have not been adequately addressed. In this study, we propose a rational and effective approach to simultaneously overcome these challenges by embedding stannous sulfide (SnS) quantum dots (QDs) within a crosslinked nitrogen (N) and sulfur (S) co-doped carbon fiber network (SnS-CFN). The well-dispersed and densely packed SnS QDs, measuring approximately 2 nm, not only minimize the diffusion distance of Na+/K+ ions but also buffer the volume expansion effectively. The N, S co-doped carbon fiber network in SnS-CFN serves as a highly conductive and stable support structure that inhibits SnS QDs aggregation, creates ion/electron transport channels, and alleviates volume variations. Density functional theory (DFT) calculations further confirm that the combination of SnS QDs and the N, S co-doped carbon effectively reduces the adsorbed energies in the interlayer of SnS-CFN. These advantages synergistically contribute to the exceptional sodium/potassium storage performance of the SnS-CFN composite. Consequently, SnS-CFN demonstrates exceptional cyclability, retaining a capacity of 251.5 mAh/g over 10,000 cycles, and exhibits excellent rate capability (299.5 mAh/g at 20 A/g) when employed in SIBs. When used in PIBs, a high capacity of 112.3 mAh/g at 2 A/g after 1000 cycles, a remarkable capacity of 51.4 mAh/g at 5 A/g after 10,000 cycles, and a remarkable rate capability with a specific capacity of 55.5 mAh/g at a high current density of 20 A/g have been achieved.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Effect of hydrophobic silica aerogels in-situ on encapsulation the stability of CsPbBr3 quantum dots for white light-emitting diodes

Despite the outstanding optical features of lead halide perovskite quantum dots (QDs), they are troubled by stability issues that hinder their prospects in practical applications. Herein, the CsPbBr3 QDs generated here were grown in situ in hydrophobic silica aerogels (SiO2 AGs). More importantly, the photoinitiated cross-linking reaction of the capping ligands, conjugated linoleic acids (CLA), forms hydrophobic polymer shells from CsPbBr3 QDs@SiO2 AGs-poly. And these polymer shells further improve the water stability of QDs. The composite retains 83 % photoluminescence (PL) intensity after being dispersed in water for five days. And SiO2 AGs also act as confined templates owing to their unique porous structure to avoid aggregation and regrowth of QDs in the polymerization process of CLA. With the combined effects of SiO2 AGs and polymer shells, the composite shows remarkable optical performance with a high absolute quantum yield (QY) (89.08 %). And this green-emitting composite was applied as a luminescent material in a white light-emitting diode (WLED), which exhibited excellent luminescence with the color coordinates of (0.3344, 0.3253) and light efficiency of 28.8 lm/W at 20 mA, and light stability under large current.

Co-sensitising cadmium selenide and cadmium telluride quantum dots on titanium dioxide nanorods via the SILAR method

Co-sensitised CdSe/ CdTe quantum dots (QDs) on the surface of TiO2 nanorods were fabricated via different cycles of successive ionic layer adsorption and reaction (SILAR) method. The deposition of the QDs onto TiO2 nanorods were confirmed with transmission electron microscopy. A higher number of SILAR cycles has led to QDs aggregation and overgrowth on the top layer of the TiO2 nanorods layer. Furthermore, the higher number SILAR cycles also lowered the charge transfer resistance as observed in the electrochemical impedance spectroscopy analysis. Based on the observation, 5 cycles were selected to be the optimized number of SILAR cycle. The sequential deposition of CdTe QDs increased the absorption intensity and extended the absorption spectra, demonstrating co-sensitisation effects, which increase the short circuit current density from 0.103 mA cm−2 to 0.158 mA cm−2 is shown to enhance the CdSe quantum dots sensitised solar cells (QDSSC) efficiency from 0.009 % to 0.018 %.

Solvothermal synthesis of CoCeSx quantum dots based on Bi-pyrene-terminated molecular wires modified porous graphene for high performance supercapacitors

Transition metal quantum dots (QDs) have attracted enormous attention in the field of energy storage in recent years due to their unique nano-size effect and flexible surface functionalities. It is worth noting that the aggregation of QDs will lead to the decline of electrochemical performance, so it is necessary to maintain its good dispersion stability. Bi-pyrene-terminated molecular wires (BPMW) can reduce the stacking of graphene, which is considered to be a good material for modifying graphene with desired porous structure, higher specific surface area, and more attachment sites for the loading of QDs. Here, rGO@BPMW@CoCeSx-QDs were successfully designed and constructed. In detail, CoCe bimetallic organic framework (CoCe-MOF) was grown in situ on BPMW modified graphene by two-step solvothermal method to afford porous composites of rGO@BPMW@CoCeSx-QDs (pore size range is 40–230 nm). The fabricated electrode based on rGO@BPMW@CoCeSx-QDs shows an excellent electrochemical capacitance of 1047 F g−1 at the current density of 1 A g−1 in a three-electrode system. Moreover, a solid-state asymmetric supercapacitor (ASC) device can be fabricated based on the synthesized rGO@BPMW@CoCeSx-QDs, and exhibits a high energy density of 32.3 Wh kg−1 at a power density of 750 W kg−1.

Transparent Nanocomposites Comprising Ligand-Exchanged CuInS2/ZnS Quantum Dots and UV-Cured Resin for Wavelength Converters

Quantum dots (QDs) dispersed in UV-curable resin are used for patterning in photolithography and inkjet printing. However, low affinity between the main component of UV-curable resins known as celloxide, an alicyclic diepoxy compound, and QD surface ligands with alkyl chains causes significant aggregation of QDs. In this study, the dispersibility of core/shell CuInS2/ZnS QDs with adsorbed 1-dodecanethiol and oleic acid in celloxide was improved using the ligand exchange method to prepare transparent fluorescent nanocomposites. Cyclohexyl 3-mercaptopropionate (MPACH) and 3-mercaptopropionic acid (MPA) were successfully adsorbed onto the QDs. MPACH-modified QDs (QD-MPACH) were well dispersed in the UV-curable resin, whereas MPA-modified QDs (QD-MPA) exhibited significant aggregation. Nanocomposite plates containing dispersed QDs were prepared by UV irradiation. The QD-MPACH nanocomposite plate was transparent, while the QD-MPA nanocomposite plate was turbid. The homogeneous dispersion of QD-MPACH was attributed to the similarity in the molecular structure between MPACH and celloxide. The photoluminescence (PL) peak of the QD-MPA nanocomposite occurred at a longer wavelength than that of the QD-MPACH nanocomposite. Furthermore, compared with the absolute photoluminescence quantum yield (PLQY) of the as-prepared QDs in toluene (55%), that of the QD-MPA nanocomposite was smaller (46%), and that of the QD-MPACH nanocomposite was higher (61%). An enhanced self-absorption effect was observed for the QD-MPA nanocomposite because of significant light scattering by the aggregates and concentration quenching, resulting in the PL redshift and decreased PLQY. Moreover, the PL intensity of the QD-MPACH nanocomposite was maintained at 98% of the initial value after continuous excitation-light irradiation for 5 h. The high PLQY and photostability of the QD-MPACH nanocomposite are beneficial in practical applications.

In situ-Synthesized cadmium sulfide quantum dots in pore-forming protein and polysaccharide matrices for optical biosensing applications

The main limitation for practical implementation of quantum dots-based sensors and biosensors is the possible contamination of sensing media with quantum dots (QDs) moved out from the sensor structure, being critical for living systems measurements. Numerous efforts have addressed the challenge of pre-synthesized QDs incorporation into porous matrix provide, on the one hand, proper fixation of quantum dots in its volume and preserving a free analyte transfer from the sensing media to them - on the other hand. Here, we propose an alternative insight into this problem. Instead of using preliminary synthesized particles for doping a matrix, we have in situ synthesized cadmium sulfide QDs in porous biopolymeric matrices, both in an aqueous solution and on a mica substrate. The proposed technique allows obtaining QDs in a matrix acting simultaneously as a ligand passivating surface defects and preventing QDs aggregation. The conjugates were used as a photoluminescence sensor for the metal ions and glutathione detection in an aqueous media. Different kinds of sensor responses have been found depending on the analyte nature. Zinc ions' presence initiates the intraband QDs emission increases due to the reduction of non-radiative processes. The presence of copper ions, in contrast, leads to a gradual photoluminescence decrease due to the formation of the non-luminescent copper-based alloy in the QDs structure. Finally, the presence of glutathione initiates a ligand exchange process followed by some QDs surface treatment enhancing defect-related photoluminescence. As a result, three different kinds of sensor responses for three analytes allow claiming development of a new selective QD-based sensor suitable for biomedical applications.

Transient Out‐of‐Equilibrium Nucleic Acid‐Based Dissipative Networks and Their Applications

AbstractDynamic, dissipative reactions play important roles in biological processes, and emulating such biological processes by artificial circuits and networks is a challenging topic in the area of Systems Chemistry. The present article summarizes efforts to apply the information encoded in the base sequence of nucleic acids to assemble transient, dissipative DNA‐based networks mimicking natural processes. The design principles of the transient nucleic acid‐based systems are introduced. Triggered reaction moduli lead to a transient intermediary constituent recovered to the parent moduli by enzymes, DNAzyme, or light as control units are described. Transient DNA‐based circuitries of enhanced complexities revealing temporal gated or cascaded transformations are demonstrated. Different applications of dynamically triggered transient circuits are introduced, including the temporal aggregation and deaggregation of plasmonic nanoparticles or semiconductor quantum dots and the control over their optical properties, the transient release and uptake of loads by aptamer scaffolds, and the transient reconfiguration of constitutional dynamic networks and the control over emergent catalytic functions. The future perspectives of dissipative nucleic acid‐based networks and their potential future applications are discussed.

Ligand-mediated CsPbBr x I3− x /SiO2 quantum dots for red, stable and low-threshold amplify spontaneous emission

The red-emitting perovskite material has received widespread attention as a long-wavelength optical gain media. But the easy phase change in the air limits its practical application. Herein, red CsPbBr x I3−x /SiO2 quantum dots (QDs) are prepared by a ligand-mediated hot injection method in which 3-aminopropyl-triethoxysilane (APTES) is used instead of the usual oleylamine (OAm) ligand. Through the hydrolysis of amino groups, a thin silicon layer is formed on the QD surface, improving the stability and without causing the aggregation of QDs. We find that the ratio of I/Br and the size of QDs can be tuned by adjusting the APTES amount. Moreover, this ligand-mediated synthesis effectively passivates the surface defects, so the photoluminescence quantum yield is remarkably improved, and the carrier lifetime is prolonged. The amplified spontaneous emission is achieved under 532 nm nanosecond laser excitation. Compared with the original CsPbBrI2-OAm QD films, the threshold of CsPbBr x I3−x /SiO2 QD films is reduced from 403.5 to 98.7 μJ cm−2, and the radiation stability is significantly enhanced. Therefore, this material shows great potential in the random laser field.

Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: Effects of ionic strength, electrolyte type, and natural organic matter

Understanding the stability and aggregation of nanoparticles in aqueous milieu is critical for assessing their behavior in the natural and engineered environmental systems and establishing their threat to human and ecosystems health. In this study, the colloidal stability and aggregation kinetics of nanocrystal quantum dots (QDs) —CdSe/ZnS QDs—were thoroughly explored under a wide range of aqueous environmental conditions. The z-average hydrodynamic diameters (z-avg. HDs) and zeta potential (ξ potential) of CdSe/ZnS QDs were measured in monovalent electrolyte (NaCl) and divalent electrolyte (CaCl2) solutions in both the absence and presence of natural organic matter (NOM)—Suwannee River natural organic matter, SRNOM to assess the dynamic growth of these nanoaggregate-QD-complexes, and the evaluation of their colloidal stability. Results show that CaCl2 was more effective to destabilize the QDs compared to NaCl at similar concentrations. An increase in NaCl concentration from 0.01 to 3.5 M increased the z-avg. HD of QD aggregates from 61.4 nm to 107.2 nm. The aggregation rates of QDs increased from 0.007 to 0.042 nm·s−1 with an increase in ionic strength from 0.5 to 3.5 M NaCl solutions, respectively. In the presence of Na+ cations, the aggregation of QDs was limited as steric forces generated by the original surface coating of QDs prevailed. In the presence of CaCl2, the aggregation of QDs was observed at a low concentration of CaCl2 (0.0001 M) with a z-avg. HD of 74.2 nm that significantly increased when the CaCl2 was higher than 0.002 M. Larger sizes of QD aggregates were observed at each level of CaCl2 concentration in suspensions of 0.002–0.1 M, as the z-avg. HDs of QDs increased from 125.1 to 560.4 nm, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 M to 0.004 M, respectively. With Ca2+ cations, the aggregation of QDs was enhanced due to the bridging effects from the formation of complexes between Ca2+ cations in solution and the carboxyl group located on the surface coating of QDs. In the presence of SRNOM, the aggregation of QDs was enhanced in both monovalent and divalent electrolyte solutions. The degree of aggregation formation between QDs through cation-NOM bridges was superior for Ca2+ cations compared to Na+ cations. The presence of SRNOM resulted in a small increase in the size of the QD aggregates for each of NaCl concentrations tested (i.e., 0.01 to 3.5 M, except 0.1 M), and induced a monodispersed and narrower size distribution of QDs suspended in the monovalent electrolyte NaCl concentrations. In the presence of SRNOM, the aggregation rates of QDs increased from 0.01 to 0.024 nm 1 with the increase of NaCl concentrations from 0.01 to 2 M, respectively. The presence of SRNOM in QDs suspended in divalent electrolyte CaCl2 solutions enhanced the aggregation of QDs, resulting in the increase of z-avg. HDs of QDs by approximately 19.3%, 42.1%, 13.8%, 1.5%, and 24.8%, at CaCl2 concentrations of 0.002, 0.003, 0.005, 0.01, and 0.1 M, respectively. In the case of CaCl2, an increase in aggregation rates occurred from 0.035 to 0.865 nm·s−1 with an increase in ionic strength from 0.0001 to 0.004 M, respectively. Our findings demonstrated the colloidal stability of QDs and cations-NOM-QD nanoparticle complexes under a broad spectrum of conditions encountered in the natural and engineered environment, indicating and the potential risks from these nanoparticles in terms of human and ecosystem health.

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

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

Restriction‐In‐Motion of Surface Ligands Enhances Photoluminescence of Quantum Dots—Experiment and Theory

AbstractThe relationship between emission and ligand restriction of a series of ZnSe/ZnS quantum dots (QDs) encapsulated in nanoparticles is investigated systematically via experiments and quantum theory. The QDs have a ZnSe core and a ZnS shell, capped with hydrophobic ligands (triotylphosphine oxide/hexadecylamine), allowing them to be entrapped in a model biomembrane, bicelle, made of zwitterionic dipalmitoyl and dihexanoyl phosphatidylcholines and charged dipalmitoyl phosphatidylglycerol. Enhanced photoluminescence is observed upon encapsulation, depending on the QD‐to‐lipid ratio. Transmission electron microscopy and small‐angle X‐ray scattering confirm that QDs are preferably situated at the rim of bicellar discs. A simplified quantum dissipation heat‐bath theory is proposed to correlate the enhancement with slower nonradiative processes caused by the restriction‐in‐motion (RIM) of the surface ligands. However, Förster resonance energy transfer due to QD aggregation counteracts the effect.