Surface Of Quantum Dots Research Articles

Despite Challenges, QD Vision Laid the Foundation for Quantum‐Dot Displays

Despite Challenges, QD Vision Laid the Foundation for Quantum‐Dot Displays

Aggregation Control, Surface Passivation, and Optimization of Device Structure toward Near‐Infrared Perovskite Quantum‐Dot Light‐Emitting Diodes with an EQE up to 15.4% (Adv. Mater. 18/2022)

Perovskite Light-Emitting Diodes A comprehensive optimization strategy leads to high-efficiency near-infrared quantum dot (QD)-based light-emitting diodes (QLEDs), as reported in article 2109785 by Zong-Liang Tseng, Shun-Wei Liu, Ken-Tsung Wong, and co-workers. Post-treatment of encapsulated FAPbI3 QDs reduces QD surface defects, and the passivated QDs dispersed in n-octane are effectively spin-coated on top of a treated electrode, leading to full-coverage, smooth, and dense QD films. The resulting QLED devices have electroluminescence λmax at 772 nm with external quantum efficiency up to 15.4% at a current density of 0.54 mA cm−2 (2.6 V).

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.

Fabrication of a near-infrared fluorescence-emitting SiO2-AuZnFeSeS quantum dots-molecularly imprinted polymer nanocomposite for the ultrasensitive fluorescence detection of levamisole

Levamisole is an anthelminthic drug that is usually used as a cutting agent to lace illicit cocaine samples and has been classified as a dangerous substance. In this work, we report on the fabrication of a novel fluorescence sensor for levamisole using AuZnFeSeS alloyed quantum dots (QDs)-molecularly imprinted polymer (MIP) nanocomposite. Firstly, organic-phased AuZnFeSeS QDs were synthesized via the organometallic hot-injection pyrolysis of metal precursors, surfactants, and organic ligands. Silica (SiO2) was then encapsulated on the QDs surface to render it compact, stable, and biocompatible. Via a free radical polymerization approach, a robust MIP shell templated with levamisole was coated around the SiO2-AuZnFeSeS QDs surface to form a AuZnFeSeS QDs@MIP core/shell nanocomposite. Passivation of the SiO2-AuZnFeSeS QDs core surface with the MIP shell led to radiative exciton recombination process, whereby the QDs fluorescence was enhanced. Interestingly, the SiO2-AuZnFeSeS QDs was characterized by rod-shaped and spherical-shaped particle morphology. Under optimum conditions, the fluorescence of the AuZnFeSeS QDs@MIP nanocomposite was quenched in the presence of levamisole and was selective against other tested drugs. Quantitative detection was achieved in the concentration range of 0.5 – 100 μM with a limit of detection of 0.05 μM (47.4 nM). Validation of the MIP-levamisole affinity was demonstrated by the superior sensitivity of the AuZnFeSeS QDs@MIP over the AuZnFeSeS QDs@NIP (non-templated material). Levamisole was successfully detected in a mixed drug sample containing cocaine with satisfactory analytical recoveries. This work is the first reported use of a cadmium-free quintenary alloyed QDs@MIP nanocomposite fluorescence detection system for levamisole.

Biomolecular Surface Functionalization and Stabilization Method to Fabricate Quantum Dots Nanobeads for Accurate Biosensing Detection.

The surface functionalization of quantum dots (QDs) is essential for their application as a label material in a biological field. Here, a protein surface functionalization approach was introduced to combine with silica encapsulation for the sustainable and stable synthesis of QDs nanobeads for biomarker detection. The formation of QDs nanobeads was achieved by multiple mercapto groups in bovine serum albumin (BSA) macromolecules as multidentate ligands to replace hydrophobic ligands on the surface of QDs and decompression. The resulting QDs nanobeads exhibited 20 times more photoluminescence than the corresponding hydrophobic QDs and presented excellent stability under physiological conditions due to the protection of BSA and silica. The nanobeads served as a robust signal-generating reagent to construct the lateral flow immunoassay (LFIA) biosensor for the detection of glycosylated hemoglobin (HbA1c). The concentration of HbA1c was determined within 10 min with high specificity using only 60 μL of whole blood samples collected clinically. The nanobeads-based LFIA biosensor exhibited linear detection of HbA1c from 4.2% to 13.6%. The accuracy and stability of this approach in clinical utility was demonstrated by the detection of HbA1c after a long-term storage of test strips. This protein surface modification technology provides a new way for improving the biological properties of QDs in clinical diagnosis.

Molecular Structure of Single-Stranded DNA on the ZnS Surface of Quantum Dots.

DNA-based nanoparticle assemblies have emerged as leading candidates in the development of bioimaging materials, photonic devices, and computing materials. Here, we combine atomistic simulations and experiments to characterize the wrapping mechanism of chimeric single-stranded DNA (ssDNA) on CdSe-ZnS (core-shell) quantum dots (QDs) at different ratios of the phosphorothioate (PS) modification of the bases. We use an implicit solvent, all-atom ssDNA model to match the experimentally calculated ssDNA conformation at low salt concentrations. Through simulation, we find that 3-mercaptopropionic acid (MPA) induces electrostatic repulsion and O-(2-mercaptoethyl)-Ó-methyl-hexa (ethylene glycol) (mPEG) induces steric exclusion, and both reduce the binding affinity of ssDNA. In both simulation and experiment, we find that ssDNA is closer to the QD surface when the QD size is larger. The effect of the PS-base ratio on the conformation of ssDNA is also elaborated in this work. We found through MD simulations, and confirmed by transmission electron microscopy, that the maximum valence numbers are 1, 2, and 3 on QDs of 6, 9, and 14 nm in diameter, respectively. We conclude that the maximum ssDNA valence number is linearly related to the QD size, n ∝ R, and justify this finding through an electrostatic repulsion mechanism.

Electron Delocalization in CsPbI3 Quantum Dots Enables Efficient Light‐Emitting Diodes with Improved Efficiency Roll‐Off

AbstractPerovskite quantum dot (QD) charging is prone to occur during light‐emitting diode (LED) operation due to the electron accumulation inside the QD emitters, which is caused by the unbalanced charge injection and carrier transportation. Here in order to address this issue, an electron attractor of phenethylammonium (PEA+) is introduced to the surface of perovskite QDs. The PEA+ conjugated ligands can reversibly store and release electrons driven by the electron local density of states redistribution, which enhances the delocalization of electrons in QDs, and thus suppresses QD charging at high carrier concentrations, as evidenced by the excitation energy dependent photoluminescence. Besides, PEA+ down‐shifts the Fermi level of perovskite QDs, consequently increases the hole concentration, leading to greatly improved hole conduction. Halogen‐rich synthesis environment also reduces the number of halogen vacancies, consequently narrows the distribution of electronic states at the band edges, leading to slightly improved electron conduction. Taking advantage of the enhanced electron delocalization and improved charge transportation, the CsPbI3 QDs LEDs show the maximum external quantum efficiency (EQE) of 15.6% with a low efficiency roll‐off, and the maximum luminance of 1634 cd m−2.

Selective and Sensitive Fluorometric Determination of Piroxicam Based on Nitrogen-doped Graphene Quantum Dots and Gold Nanoparticles Coated with Phenylalanine.

In this study, a sensitive fluorimetric method is proposed for the determination of piroxicam using nitrogen graphene quantum dots (N-GQDs) and gold nanoparticles coated with phenylalanine. The fluorescence emission of N-GQDs at 440nm decreases with the increase of gold nanoparticles coated with phenylalanine. However, the addition of piroxicam causes the release of gold nanoparticles from the surface of quantum dots followed by the retrieval of the fluorescence emission of N-GQDs. Under the optimum conditions, the calibration graph was linear in the concentration range of 2.0-35.0nmol L-1 for piroxicam with a limit of detection of 0.11nmol L-1. The developed method was successfully applied for the determination of piroxicam in urine and serum samples.

Construction of ratio fluorescence sensor based on CdTe quantum dots and benzocoumarin-3-carboxylic acid for Hg2+ detection

A new ratio fluorescence sensor based on mercaptamine capped cadmium telluride quantum dots (Mea-CdTe) and benzocoumarin-3-carboxylic acid (BTA) were constructed. The ratio fluorescence sensor ([email protected]) was synthesized by amidation reaction between the amino groups on the surface of Mea-CdTe quantum dots and the carboxyl groups of BTA. It is found that Hg2+ ions react with the amino groups on the surface of the quantum dots in the [email protected] sensor to quench the fluorescence, but it has no effect on the fluorescence of grafted BTA. The sensor has good selectivity and high sensitivity for Hg2+ ions detection. The detection linear range is 0.4–1.2 µM, and the detection limit is 0.03 µM. This ratio fluorescence sensor can be used for Hg2+ visual recognition in water sample detection with obvious color change.

Aggregation Control, Surface Passivation, and Optimization of Device Structure toward Near-Infrared Perovskite Quantum-Dot Light-Emitting Diodes with an EQE up to 15.4.

In recent years, the performance of perovskite quantum dots (QDs) and QD-based light-emitting diodes (QLEDs) has improved greatly, with electroluminescence (EL) efficiency of green and red emission exceeding 20%. However, the development of perovskite near-infrared (NIR) QLEDs has reached stagnation, where the reported maximum EL efficiency is still below 6%, limiting their further applications. In this work, new NIR-emissive FAPbI3 QDs are developed by post-treating long alkyl-encapsulated QDs with 2-phenylethylammonium iodide (PEAI). The incorporation of PEAI reduces the QD surface defects for giving a high photoluminescence quantum yield up to 61.6%. The n-octane solution of PEAI-passivated FAPbI3 QDs is spin coated on top of the PEDOT:PSS-treated ITO electrode modified with a thermally crosslinked hole-transporting layer to give a full-coverage, smooth, and dense QD film. Incorporating with an effective electron-transporting material, CN-T2T, which has deep lowest unoccupied molecular orbital and good electron mobility, the optimal device with EL λmax at 772nm achieves an external quantum efficiency up to 15.4% at a current density of 0.54mA cm-2 (2.6V), which is the highest efficiency ever reported for perovskite-based NIR QLEDs. This study provides a facile strategy to prepare high-quality perovskite QD films suitable for highly efficient NIR QLED applications.

Molecular Dynamics Simulations of Docetaxel Adsorption on Graphene Quantum Dots Surface Modified by PEG-b-PLA Copolymers.

Cancer is associated with a high level of morbidity and mortality, and has a significant economic burden on health care systems around the world in almost all countries due to poor living and nutritional conditions. In recent years, with the development of nanomaterials, research into the drug delivery system has become a new field of cancer treatment. With increasing interest, much research has been obtained on carbon-based nanomaterials (CBNs); however, their use has been limited, due to their impact on human health and the environment. The scientific community has turned its research efforts towards developing new methods of producing CBN. In this work, by utilizing theoretical methods, including molecular dynamics simulation, graphene quantum dots (GQD) oxide was selected as a carbon-based nanocarriers, and the efficiency and loading of the anticancer drug docetaxel (DTX) onto GQD oxide surfaces in the presence and in the absence of a PEG-b-PLA copolymer, as a surface modifier, were investigated. According to the results and analyzes performed (total energy, potential energy, and RMSD), it can be seen that the two systems have good stability. In addition, it was determined that the presence of the copolymer at the interface of GQD oxide delays the adsorption of the drug at first; but then, in time, both the DTX adsorption and solubility are increased.

Preparation and evaluation of a double-hydrophilic interaction stationary phase based on bovine serum albumin and graphene quantum dots modified silica

The bovine serum albumin (BSA) was firstly bonded on the surface of graphene quantum dots (GQDs) functionalized silica as the stationary phase named as BSA@GQDs@SiO2 which can perform hydrophilic interaction between the stationary phase and analytes. Characteristic methods including Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), thermogravimetric analysis (TGA) and scanning electron microscope (SEM) were applied to estimate the chemical bonding results and morphological features of the prepared materials. In the chromatographic evaluation part, the BSA@GQDs@SiO2 column showed excellent separation efficiency for the analysis of hydrophilic compounds involving nucleosides and bases, acids, phenols, quinolones, vitamins and alkaloids, which proved the prepared column can exhibit hydrophilic interaction mode with other interactions including hydrogen bonding and electrostatic interaction. What's more, essential experimental approaches were designed to evaluate the retention properties of the prepared column via comparing with a commercial amino column and a prepared GQDs@SiO2 column. Results indicated the prepared column showed excellent separation ability for different kinds of hydrophilic compounds than commercial and single hydrophilic columns. The study showed that BSA@GQDs@SiO2 stationary phase with double hydrophilic materials will be a potential chromatographic material for analyzing various hydrophilic analytes.

Luminescence color regulation of carbon quantum dots by surface modification

Labelling various biological molecules with multi-color carbon quantum dots (CQDs) in the same scene has great potential application for investigating the relationship between those molecules. It is still a great challenge to regulate the color of CQDs. Ample –NH2 groups on the surface of green carbon quantum dots (GCQDs) were characterized and confirmed by 1H nuclear magnetic resonance (1H NMR) data. As–NH2 groups had high organic reactivity, the surface of GCQDs was designed and modified with several organic functional groups through a simple surface modification strategy of organic reactions. The surface band gap states of GCQDs were tuned gradually by the corresponding modified functional groups, and the emission colors of GCQDs were tuned from green to yellow-green, then to orange, and finally to red. All the emission spectra for these multicolor carbon quantum dots (M-CQDs) were excitation independent, and the lifetimes for the M-CQDs were mainly determined by the second electron decay process from the surface defect band states. The red-shift colors for the M-CQDs were ascribed to the emissions from their surface defect band states, and the luminescence mechanism had been investigated. This work opens up a novel synthesis strategy to regulate the emission colors of carbon quantum dots.

Stability and luminescence properties of CsPbBr3/CdSe/Al core-shell quantum dots

To improve the stability and luminescence properties of CsPbBr3 QDs, we proposed a new core-shell structure for CsPbBr3/CdSe/Al quantum dots (QDs). By using a simple method of ion layer adsorption and a reaction method, CdSe and Al were respectively packaged on the surface of CsPbBr3 QDs to form the core-shell CsPbBr3/CdSe/Al QDs. After one week in a natural environment, the photoluminescence quantum yields of CsPbBr3/CdSe/Al QDs were greater than 80%, and the PL intensity remained at 71% of the original intensity. Furthermore, the CsPbBr3/CdSe/Al QDs were used as green emitters for white light-emitting diodes (LEDs), with the LEDs spectrum covering 129% of the national television system committee (NTSC) standard color gamut. The core-shell structure of QDs can effectively improve the stability of CsPbBr3 QDs, which has promising prospects in optoelectronic devices.

Strategies of Improving CsPbX3 Perovskite Quantum Dots Optical Performance

All-inorganic perovskite quantum dots (QDs) (CsPbX3, X = Cl, Br, I) become promising candidate materials for the new generation of light-emitting diodes for their narrow emission spectrum, high photoluminescence quantum yield, and adjustable emission wavelength. However, the perovskite QDs materials still face instability against moisture, high-temperature, and UV-light. Many strategies have been reported to improve the photoluminescence (PL) performance of QDs while increasing their stability. These strategies can be divided into three main categories: doping engineering, surface ligand modification, coating strategies. This paper reviews the recent research progress of surface ligands, inorganic and polymer coating, and metal ions doping of CsPbX3 QDs. Partial substitution of Pb2+ with non-toxic or low-toxic metal ions can improve the formation energy of the perovskite lattice and reduce its toxicity. The surface polymer modification can use their ligands to bond with the uncoordinated lead and halogen ions on perovskite QDs surface to reduce surface defects, thereby improving the PL intensity and stability. In addition, the organic or inorganic coating materials on perovskite QDs can effectively avoid their contact with the external environment, thereby improving the stability of the perovskite. The optical properties of the modified QDs, including transient absorption spectra, temperature-dependent PL spectra, time-resolved photoluminescence (TRPL) spectra properties, etc. were discussed to explain the physical mechanism. The potential applications of all-inorganic perovskite QDs as down-conversion fluorescent materials in light-emitting diodes are presented. Finally, we provide some possible methods to further improve the PL performance of the all-inorganic perovskite QDs.

Carrier Injection to In0.4Ga0.6As/GaAs Surface Quantum Dots in Coupled Hybrid Nanostructures

Stacking growth of the InGaAs quantum dots (QDs) on top of a carrier injection layer is a very useful strategy to develop QD devices. This research aims to study the carrier injection effect in hybrid structures with a layer of In0.4Ga0.6As surface quantum dots (SQDs), coupled to an injection layer of either one layer of In0.4Ga0.6As buried QDs (BQDs) or an In0.15Ga0.85As quantum well (QW), both through a 10 nm GaAs thin spacer. Spectroscopic measurements show that carrier capture and emission efficiency for SQDs in the BQD injection structure is better than that of the QW injection, due to strong physical and electrical coupling between the two QD layers. In the case of QW injection, although most carriers can be collected into the QW, they then tunnel into the wetting layer of the SQDs and are subsequently lost to surface states via non-radiative recombination. Therefore, the QW as an injection source for SQDs may not work as well as the BQDs for stacking coupled SQDs structures.

Rapid detection of ciprofloxacin in seawater based on CdTe quantum dots coated with molecularly imprinted polymers

In this work, a sensitive fluorescent sensor for the detection of ciprofloxacin (CIP) was developed by wrapping the surface of CdTe quantum dots (QDs) with molecularly imprinted polymers (MIPs). The MIP@QDs were synthesized via a simple sol–gel method using 3-aminopropyltriethoxysilane (APTES) as the functional monomer and tetraethoxysilane (TEOS) as the crosslinker. The fluorescence emission of the probe was at 643 nm. Linear calibration curves were obtained in the range of 0.5–24 [Formula: see text]M for CIP with the detection limit of 0.23 [Formula: see text]M (S/N[Formula: see text]3). The fluorescent probe was successfully applied to the determination of CIP in seawater samples with the spiked recoveries ranging from 98.2% to 110.6% and the relative standard deviation (RSD) was less than 10.7%. It is the first time that QDs with molecularly imprinted polymers (MIP@QDs) were introduced for separation and detection of CIP in seawater and obtained good specific identification ability and potential practical value.

Efficient and Stable CF3PEAI-Passivated CsPbI3 QDs toward Red LEDs.

Oleylamine and oleic acid are common organic capping ligands used in the hot injection preparation of perovskite quantum dots (QDs). Their labile nature is responsible for the poor colloidal stability and conductivity that affect the performance of perovskite QD light-emitting diodes (LEDs). We introduced 4-trifluoro phenethylammonium iodide (CF3PEAI) directly in the synthesis and found that CF3PEAI efficiently modified the I- vacancy defects on the QD surface and partially substituted the surface capping ligand oleylamine. The strong electron pulling ability of F in CF3PEAI results in a more positive -NH3+ terminal compared to that of PEAI, which promotes tight bonding of CF3PEAI on the surface of CsPbI3 QDs. As a result, we achieved bright QDs with a photoluminescence quantum yield of 92% and efficient red LEDs. The maximal luminance was improved to 4550 cd m-2 for 685 nm red light, which was nearly 4.6-fold of the LEDs with plain CsPbI3 QDs. Additionally, the peak external quantum efficiency reached 12.5%.

Influence of donor-to-acceptor ratio on excited-state electron transfer within covalently tethered CdSe/CdTe quantum dot colloidal heterostructures.

Carbodiimide-mediated coupling chemistry was used to synthesize heterostructures of CdSe and CdTe quantum dots (QDs) with varying ratios of electron-donating CdTe QDs and electron-accepting CdSe QDs. Heterostructures were assembled via the formation of amide bonds between the terminal functional groups of CdTe-adsorbed 4-aminothiophenol (4-ATP) ligands and CdSe-adsorbed N-hydroxysuccinimide (NHS) ligands. The number of charge acceptors on the surfaces of QDs can greatly influence the rate constant of excited-state charge transfer with QDs capable of accommodating far more acceptors than molecular chromophores. We report here on excited-state electron transfer within heterostructure-forming mixtures of 4-ATP-capped CdTe and NHS-capped CdSe QDs with varying molar ratios of CdTe to CdSe. Photophysical properties and charge transfer were characterized using UV-vis absorption, steady-state emission, and time-resolved emission spectroscopy. As the relative concentration of electron-accepting CdSe QDs within mixtures of 4-ATP-capped CdTe and NHS-capped CdSe QDs increased, the rate and efficiency of electron transfer increased by 100-fold and 7.4-fold, respectively, as evidenced by dynamic quenching of band-edge emission from CdTe QDs. In contrast, for non-interacting mixtures of thiophenol capped CdTe QDs and NHS-capped CdSe QDs, which served as control samples, photophysical properties of the constituent QDs were unperturbed and excited-state charge transfer between the QDs was negligible. Our results reveal that carbodiimide-mediated coupling chemistry can be used to control the relative number of donor and acceptor QDs within heterostructures, which, in turn, enables fine-tuning of charge-transfer dynamics and yields. These amide-bridged dual-QD heterostructures are, thus, intriguing for light harvesting, charge transfer, and photocatalysis.

Photobase-Triggered Formation of 3D Epitaxially Fused Quantum Dot Superlattices with High Uniformity and Low Bulk Defect Densities

Highly ordered epitaxially fused colloidal quantum dot (QD) superlattices (epi-SLs) promise to combine the size-tunable photophysics of QDs with the efficient charge transport of bulk semiconductors. However, current epi-SL fabrication methods are crude and result in structurally and chemically inhomogeneous samples with high concentrations of extended defects that localize carriers and prevent the emergence of electronic mini-bands. Needed fabrication improvements are hampered by inadequate understanding of the ligand chemistry that causes epi-SL conversion from the unfused parent SL. Here we show that epi-SL formation by the conventional method of amine injection into an ethylene glycol subphase under a floating QD film occurs by deprotonation of glycol by the amine and subsequent exchange of oleate by glycoxide on the QD surface. By replacing the amine with hydroxide ion, we demonstrate that any Brønsted-Lowry base that creates a sufficient dose of glycoxide can produce the epi-SL. We then introduce an epi-SL fabrication method that replaces point injection of a base with contactless and uniform illumination of a dissolved photobase. Quantitative mapping of multilayer (3D) films shows that our photobase-made epi-SLs are chemically and structurally uniform and have much lower concentrations of bulk defects compared to the highly inhomogeneous and defect-rich epi-SLs produced by amine point injection. The structural-chemical uniformity and structural perfection of photobase-made epi-SLs make them leading candidates for achieving emergent mini-band charge transport in a self-assembled mesoscale solid.