Core-shell Quantum Dots Research Articles

Near-Unity Photoluminescence Quantum Yield of Core-Only InP Quantum Dots via a Simple Postsynthetic InF3 Treatment.

Indium phosphide (InP) quantum dots (QDs) are considered the most promising alternative for Cd and Pb-based QDs for lighting and display applications. However, while core-only QDs of CdSe and CdTe have been prepared with near-unity photoluminescence quantum yield (PLQY), this is not yet achieved for InP QDs. Treatments with HF have been used to boost the PLQY of InP core-only QDs up to 85%. However, HF etches the QDs, causing loss of material and broadening of the optical features. Here, we present a simple postsynthesis HF-free treatment that is based on passivating the surface of the InP QDs with InF3. For optimized conditions, this results in a PLQY as high as 93% and nearly monoexponential photoluminescence decay. Etching of the particle surface is entirely avoided if the treatment is performed under stringent acid-free conditions. We show that this treatment is applicable to InP QDs with various sizes and InP QDs obtained via different synthesis routes. The optical properties of the resulting core-only InP QDs are on par with InP/ZnSe/ZnS core-shell QDs, with significantly higher absorption coefficients in the blue, and with potential for faster charge transport. These are important advantages when considering InP QDs for use in micro-LEDs or photodetectors.

Metal Fluorides Passivate II-VI and III-V Quantum Dots.

Quantum dots (QDs) with metal fluoride surface ligands were prepared via reaction with anhydrous oleylammonium fluoride. Carboxylate terminated II-VI QDs underwent carboxylate for fluoride exchange, while InP QDs underwent photochemical acidolysis yielding oleylamine, PH3, and InF3. The final photoluminescence quantum yield (PLQY) reached 83% for InP and near unity for core-shell QDs. Core-only CdS QDs showed dramatic improvements in PLQY, but only after exposure to air. Following etching, the InP QDs were bound by oleylamine ligands that were characterized by the frequency and breadth of the corresponding ν(N-H) bands in the infrared absorption spectrum. The fluoride content (1.6-9.2 nm-2) was measured by titration with chlorotrimethylsilane and compared with the oleylamine content (2.3-5.1 nm-2) supporting the formation of densely covered surfaces. The influence of metal fluoride adsorption on the air stability of QDs is discussed.

Heterointerface Effects on Carrier Dynamics in Colloidal Quantum Dots and Their Application to Light-Emitting Diodes.

Colloidal quantum dots (QDs) are promising candidates for next-generation display technology because of their unique optical properties and have already appeared in the market as a high-end product. On the basis of their extraordinary properties, QD emissions with a given chemical composition can be tailored in a wide spectral window due to quantum size effects, which constitutes a key advantage of QDs in the display field. Specifically, investigations of structure-dependent and composition-dependent characterizations outside the quantum confinement effect have become an important part of practical applications. Therefore, from the perspective of designing nanostructures with well-defined heterointerfaces, strong quantum confinement effects with effective carrier confinement are desirable. Our results show that the photoluminescence (PL) intensity of CdSe/CdZnS core-shell QDs was enhanced 5.7 times compared with that of the CdSe core QDs. Supplementary analytical techniques involving transmission electron microscopy revealed the heterointerface configuration and composition distribution of the core and shell materials. The effects of the heterointerface on carrier dynamics in core-shell QDs were revealed by monitoring wavelength-dependent time-resolved PL. To further develop the QD light-emitting diodes (QD-LEDs), we produced an all-solution processed inverted QD-LEDs using CdSe/CdZnS core-shell QDs as the emitter. The electroluminescence spectrum of deep-red emissive QD-LEDs with CIE chromaticity coordinates of (0.68, 0.32) exhibited a peak at 638 nm.

Core-shell structure N-doped graphene quantum dots Fe3O4/Co3O4 nanoparticles for colorimetric detection of H2O2

Hydrogen peroxide (H2O2) is an environmentally friendly intermediate in the environmental field and also plays an important role in human metabolism, but the production and accumulation of excessive H2O2 will cause harm to the human body, resulting in serious damage to cells. Therefore, N-doped graphene quantum dots Fe3O4/Co3O4 nanoparticles with core-shell structure were prepared by in-situ synthesis and precipitation. The experimental results show that the prepared Co3O4 nanoparticles have more efficient peroxidase activity than Co3O4 nanoparticles alone. It can catalyze the oxidation of 3, 3, 5, 5-tetramethylbenzidine (TMB) to produce a blue product (TMBox) in the presence of H2O2. In addition, Co3O4 with negative charge in the shell can produce a strong electrostatic driving coordination effect with positively charged TMB, which enhances the affinity between the nanoparticles and the substrate, and selectively catalyzes H2O2 oxidation of colorless TMB to turn it blue. Based on these experimental results, a simple, low-cost, and efficient colorimetric method for H2O2 detection was established, which showed a sensitive response to H2O2 in the range of 0.02–2.5 μM with a detection limit of 2.3 nM. In addition, due to the magnetic properties of the prepared nanoparticles, they could be easily recovered by applying a magnetic field. This research provides a viable approach for magnetic nanomaterials with encouraging prospects for environmental monitoring, biosensing, and more.

A novel fluorescent sensor for selective rifampicin detection based on the bio-inspired molecularly imprinted polymer-AgInS2/ZnS quantum dots.

A fluorescent sensing material based on the ternary core-shell quantum dots with outstanding optical properties and a bio-inspired molecularly imprinted polymer (MIP) as a recognition element has been prepared for selective detection of rifampicin (RFP). Firstly, AgInS2/ZnS core/shell quantum dots (ZAIS QDs) were prepared by a hydrothermal process. Then, the fluorescent sensor was prepared by coating these QDs by a dopamine-based MIP layer. The fluorescence of MIP@ZAIS QDs was quenched by RFP probably due to the photoinduced electron transfer process. The quenching constant was much higher for MIP@ZAIS QDs than the non-imprinted polymer@QDs, indicating that MIP@ZAIS QDs could selectively recognize RFP. Under the optimized conditions, the sensor had a good linear relationship at the RFP concentration range of 5.0 to 300nM and the limit of detection was 1.25nM. The respond time of the MIP@ZAIS QDs was 5min, and the imprinting factor was 6.3. It also showed good recoveries ranging from 98 to 101%, for analysis of human plasma samples. The method is simple and effective for the detection of RFP and offers a practical application for the rapid analysis of human plasma samples.

Impurity states in non-concentric spherical core-shell quantum dot

It was suggested the model of the non-concentric spherical core-shell quantum dot with hydrogenic impurity. It has been defined that the electron energy spectrum as a function of both an impurity and the core location. The splitting and degeneration of energy levels has been discussed. It is shown that displacing the core of a quantum dot or impurity in opposite directions can lead to alternate splitting and degeneracy of the energy levels of excited states. In certain configurations of arrangements, compensatory effects associated with the partial restoration of spherical symmetry in the field are observed.

Surface Plasmon Resonance Enhanced Photoelectrochemical Sensing of Cysteine Based on Au Nanoparticle-Decorated ZnO@graphene Quantum Dots.

In this work, Au nanoparticle-decorated ZnO@graphene core-shell quantum dots (Au-ZnO@graphene QDs) were successfully prepared and firstly used to modify an ITO electrode for the construction of a novel photoelectrochemical biosensor (Au-ZnO@graphene QDs/ITO). Characterization of the prepared nanomaterials was conducted using transmission electron microscopy, steady-state fluorescence spectroscopy and the X-ray diffraction method. The results indicated that the synthesized ternary nanomaterials displayed excellent photoelectrochemical performance, which was much better than that of ZnO@graphene QDs and pristine ZnO quantum dots. The graphene and ZnO quantum dots formed an effective interfacial electric field, enhancing photogenerated electron-hole pairs separation and leading to a remarkable improvement in the photoelectrochemical performance of ZnO@graphene QDs. The strong surface plasmon resonance effect achieved by directly attaching Au nanoparticles to ZnO@graphene QDs led to a notable increase in the photocurrent response through electrochemical field effect amplification. Based on the specifical recognition between cysteine and Au-ZnO@graphene QDs/ITO through the specificity of Au-S bonds, a light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine with an extremely low detection limit of 8.9 nM and excellent selectivity. Hence, the Au-ZnO@graphene QDs is a promising candidate as a novel advanced photosensitive material in the field of photoelectrochemical biosensing.

Carboxyl-Modified Quantum Dots for NIR-IIb Bone Marrow Imaging.

Real-time, noninvasive, and nonradiative bone imaging can directly visualize bone health but requires bone-targeted probes with high specificity. Herein, we propose that carboxyl-rich fluorescent nanoprobes are easily absorbed by macrophages in bone marrow during circulation, enabling optical bone marrow imaging in vivo. We used PbS/CdS core-shell quantum dots with NIR-IIb (1500-1700 nm) emission as substrates to prepare the carboxyl-rich nanoprobe. In vivo NIR-IIb fluorescence imaging with the nanoprobes showed high resolution and penetration depth in bone tissues and allowed for imaging-guided fracture diagnosis. Bone tissue slices showed substantial accumulation of carboxyl nanoprobes in the bone marrow and strong colocalization with macrophages. Similar results with CdSe quantum dots and an organic nanofluorophore suggest that carboxyl surface modification is effective to achieve bone marrow targeting, providing a novel strategy for developing bone/bone marrow imaging probes.

Analytical Modeling for Photocurrent and Detectivity of TiO2/ZnS Core‐Shell Quantum Dot Photodetectors

AbstractIn this paper, a theoretical model has been presented to calculate the photocurrent and detectivity in a TiO2/ZnS core‐shell quantum dot (CSQD) photodetector. Analytical modeling permits to calculate the available photocurrent and corresponding detectivity from the CSQD structures. In this theoretical model, the subband energy levels of the CSQD are estimated using the 3D symmetric quantum box structures with a finite potential barrier. The finite band offset determines the number of available subband energy levels in the CSQD structures depending on the size of the core. Theoretical results show the variation of photocurrent and corresponding detectivity with different core sizes of the CSQD for a constant shell thickness. The calculations indicate that for electronic intersubband transitions detectivity is higher compared with the hole transitions.

Analyzing photoionization cross-sectional modulation in CdSe/CdS core–shell nanodots: Impact of strain and applied electric field

The role of strain in material properties is well-established, serving as a tool for altering atomic positions and defect formation, adjusting electronic structures and lattice vibrations, and influencing phase transitions, physical characteristics, and chemical properties. In this study, we conducted theoretical calculations of the binding energy and photoionization cross section (PCS) within a spherical core/shell quantum dot (CSQD) for the different transitions between the ground state of a donor impurity and the four low-lying conduction band states. During our study, we employed the finite element method to determine the energy levels and wave functions of the system within the effective mass approximation. Subsequently, we investigated the changes in PCS and binding energy while varying shell width under the influence of an applied electric field, considering both cases with and without the effect of strain. The strain effect was incorporated based on Hooke's law, and we developed specific expressions and utilized the continuum linear elasticity mechanical model for a single spherically symmetric shell. The results demonstrate that the strain correction enhances the binding energy of the four low-lying energy levels, leading to a shift of the PCS peaks toward higher energies. Conversely, the application of an external electric field has varying effects depending on the specific transition being considered. We compared our theoretical results with available experimental data and found them to be in good agreement. The pronounced blue-shift and substantial enhancement in magnitude of PCS spectra concerning shell width, electric field, and strain make CSQDs highly promising candidates for applications in adjustable nano-optoelectronic devices.

Cumulative effect of spectral downshifting, anti-reflection and space-charge region formation in enhancing the spectral response of self-powered silicon photodetectors on sensitisation with CdZnS/ZnS core-shell quantum dots

Despite their ubiquity, Silicon (Si)-based photodetectors face intrinsic limitations that inhibit their performance, especially in the critical ultraviolet (UV) range. Downshifting of high energy photons by employing luminescent quantum dots (QDs) has up to now been the commonest photon harvesting technique in Si photodetectors. This research article describes the monolithic integration of CdZnS/ZnS core-shell QDs with Si photodetectors to make use of the spectral downshifting effect. Silicon detectors sensitised with these QDs have shown remarkably enhanced responsivity and external quantum efficiency over a broad spectral range of 300 - 1100 nm. Apart from the spectral down-shifting process, the anti-reflection effect of the QD film and the formation of a space charge region at the Si-CdZnS/ZnS interface have also contributed to enhanced device performance. The additive effect of spectral downshifting, anti-reflection effects and heterojunction formation has given these QD-sensitized devices enhanced responsivity and EQE values of 345 mA/W and 0.5, markedly higher than the values of 110 mA/W and 0.15 seen in pristine devices. Given the notable enhancement demonstrated without the need for the application of epitaxial techniques, this study may assist in mitigating the inherent limitations of Si photodetectors.

Water-soluble near-infrared CuInS2/ZnS fluorescent quantum dots for Cu2+ detection and cellular imaging

The detection and imaging of intracellular copper ions (Cu2+) play a crucial role in understanding their physiological implications and their involvement in various cellular processes. This study focuses on the synthesis and characterization of water-soluble near-infrared fluorescent CIS/ZnS core–shell quantum dots (QDs) with excellent biocompatibility and stability. The QDs exhibit exceptional selectivity and sensitivity for Cu2+ detection, allowing for precise quantification of Cu2+ content within biological systems. Furthermore, Co-incubation of the QDs with HeLa cells demonstrates their impressive cellular imaging capabilities, facilitated by fluorescence bursts in response to changing Cu2+ content. Overall, our proposed QDs are of great significance in advancing the research and application of near-infrared semiconductor quantum dots in biomedicine, and their near-infrared fluorescence properties and high fluorescence quantum yield (34.48 %) make them very advantageous for the precise detection of intracellular Cu2+ and cell fluorescence imaging. This research contributes to the understanding of copper ion dynamics within cells and opens avenues for further exploration of its role in cellular physiology.

Competitive fluorescent immunosensor based on FRET between core-shell graphene quantum dots and Au nanoparticles for ultra-sensitive detection of ochratoxin A

Ochratoxin A (OTA) is a kind of mycotoxin, and developing a sensitive and simple method to detect OTA is of great significance for ensuring food safety and human health. In this study, a competitive fluorescent immunosensor based on fluorescence resonance energy transfer (FRET) was designed for the ultra-sensitive detection of OTA. Here, Ag@SiO2 @N, S-GQDs nanocomposites were successfully designed, fabricated, and characterized by heteroatom co-doping and metal enhanced fluorescence (MEF) techniques, which can improve the fluorescence intensity and quantum yield. This study indicated that FRET between OTA antigen-modified Ag@SiO2 @N, S-GQDs (Ag@SiO2 @N, S-GQDs-OTA-Antigen) and OTA antibody-modified AuNPs can effectively quench the strong fluorescence of Ag@SiO2 @N, S-GQDs-OTA-Antigen. The competitive fluorescent immunosensor based on FRET can detect OTA with a linear range of 0.5–1000 pg/mL and a limit of detection (LOD) of 0.094 pg/mL under optimal conditions. The recoveries ranged from 94% to 110% for the red wine sample, suggesting that the developed FRET-based competitive fluorescent immunosensor can be an effective tool for the ultra-sensitive detection of OTA, meanwhile, it might provide a better method for the detection of other toxic small molecules in food and the environment.

Evidence of carrier diffusion between emission states in CdSe/ZnS core-shell quantum dots: a comprehensive investigation combining fluorescence lifetime correlation spectroscopy (FLCS) and single dot photoluminescence studies.

Investigation of carrier dynamics in CdSe/ZnS core-shell quantum dots (QDs) is performed using fluorescence-lifetime-correlation-spectroscopy (FLCS) and single-dot PL blinking studies. The origin of an emitted photon from a QD in an FLCS study is assigned to either an exciton state or trap state based on its excited state lifetime (τfl). Subsequently, two intrastate autocorrelation functions (ACFs) representing the exciton and trap states and one cross-correlation function (CCF) coupling these two states are constructed. Interestingly, the timescales of carrier diffusion (τR) show striking similarities across all three correlation functions, which further correlate with τR of the conventional FCS. However, ACFs notably deviate from the CCF in their μs progression patterns, with the latter showing growth, whereas the former ones display decay. This implies inter-state carrier diffusions leading to the QD blinking. Further study of single particle PL blinking on a surface-immobilized QD indicates shallow trap states near the band edge cause the blinking at low excitation power, while trion recombination becomes an additional contributing factor at higher pump power. Overall, the results highlight not only an excellent correlation between these two techniques but also the potential of our approach for achieving an accurate and comprehensive understanding of carrier dynamics in CdSe/ZnS QDs.

CdSe@CdS core-shell quantum dots as antifungal agents: significance of particle size and shell thickness

CdSe@CdS core-shell quantum dots as antifungal agents: significance of particle size and shell thickness

Physico-chemical properties of nanocomposites based on multi-component hybrid quantum dots

Composites of inorganic nano-objects such as quantum dots (QDs) and organic materials such as luminescent or polymers can be developed based on them for special applications such as optical devices, electro-optical devices and computing. In the study, nanocomposites based on multi-component quantum dots were obtained and nanocomposites were obtained by inserting them into polymethyl methacrylate (PMMA). First, core-shell hybrid quantum dots were synthesized, then core/shell/shell systems were obtained, and their absorption, luminescence spectra and sizes were obtained. In this work, information is presented about the opening of wide opportunities for the use of semiconductor nanocrystals related to obtaining new hybrid nanocomposite systems for nanomedicine and biomedicine.

Similarity of multicomponent nanomaterials in a safer-by-design context: the case of core–shell quantum dots

Concepts of similarity applied to complex multicomponent advanced materials for an informed balance of performance and hazard.

Effect of interfacial electronic structure on conductivity and space charge characteristics of core-shell quantum dots/polyethylene nanocomposite insulation

To investigate the effect of the interface electronic structure of core-shell quantum dots on the conductivity and space charge characteristics of polyethylene insulation, nanocomposite insulations, namely CdSe@ZnS/LDPE and ZnSe@ZnS/LDPE, are synthesized. The study focuses on elucidating the evolution patterns of DC conductivity and space charge in the nanocomposite insulation, and analyzing the effect of the interfacial electronic structure of core-shell quantum dots on the distribution of charge traps. Comparative analysis reveals that in contrast to LDPE insulation, ZnSe@ZnS/LDPE nanocomposite insulation demonstrates a substantial reduction in DC conductivity by 47.2% and a decrease in space charge accumulation by 40.3% under the conditions of elevated temperature and strong electric field. The increase of trap energy level means an enhanced trap effect on charger carriers. According to density functional theory, the band structure characteristics of core-shell quantum dots integrated with polyethylene are computationally assessed. The findings underscore that the band misalignment at the core-shell interface and the shell-insulation interface induces shifts in the conduction band bottom and at the valence band top, respectively. These shifts impose a confinement effect on electrons and holes, with the extent of this effect escalating with the augment of the difference in band gap between the core layer and the shell layer. Consequently, this phenomenon curtails carrier migration, thereby inhibiting space charge accumulation under the conditions of elevated temperature and strong electric fields.

Photo-induced single-electron tunnelling based Coulomb staircase effect observed at high applied bias in ZnSe/CdSe core-shell quantum dots

Photo-induced single-electron tunnelling based Coulomb staircase effect observed at high applied bias in ZnSe/CdSe core-shell quantum dots

Synthesis and characterization of CIS/CISe core–shell structured quantum dots in green systems

I–III–VI2 group compounds, such as CuInSe2 (CISe), and CuInS2 (CIS) quantum dots (QDs), are promising for photovoltaic applications by virtue of their excellent photoelectric properties and low toxicity. Considering that the surface of QDs with smaller sizes tends to have a larger density of defect states, inorganic shell layer modification is beneficial to passivate the surface defects and enhance the optical properties and quantum efficiency of QDs. In this study, a novel core–shell structure was constructed by growing a CISe shell layer with a narrower band gap on the surface of CIS nanocrystals with a wider band gap through a green and simple method. The components and properties of the core–shell QDs were analyzed by different characterization methods (XRD, TEM, EDS, UV–Vis, Raman, and fluorescence spectroscopy). The prepared CIS/CISe core–shell QDs with increased size and good coating effects exhibited high absorbance and extended carrier lifetime while showing quantum effects associated with the CISe shell layer, as well as a promising application in the field of solar cells.