ZnSe Quantum Dots Research Articles

Manipulation of defect state emission in Zn chalcogenide quantum dots and their effects on chlorophyll spectral response

Water soluble Zn based quantum dots (QDs) are of interest due to their biocompatibility and less toxic features. They have been frequently used in studies related to biotechnology, especially in agriculture studies. However, to control the optical properties of Zn based QDs has still been a challenge. In this work, the defect state emission of ZnSe QDs was successfully controlled through two different routes; 1) By creating a sulfur rich outer region around the Se rich core 2) By changing the capping agent. Gradient alloyed ZnSeS QDs with Se rich core and S rich outer region were successfully synthesized with two different capping agents; N-Acetyl-L-Cysteine (NAC) and 3-Mercaptopropionic Acid (3-MPA). The contribution of emission originated from surface-defects almost disappeared in NAC capped ZnSeS QDs, with causing a significant increase in photoluminescence quantum yield. The interaction between Zn based QDs with chlorophyll molecules was also investigated. The absorption capacity of chlorophylls significantly enhanced upon interaction with 3-MPA capped ZnSeS QDs. Also, the spectral response of chlorophylls could be modulated through interaction with 3-MPA capped ZnSeS QDs, which could be manipulated by using ZnSeS QDs with different chemical composition. Our results indicated that ZnSeS QDs have potential to be used in agriculture, which could act as a modulator of light-harvesting capacity of chlorophylls. The ability to modulate chlorophyll spectral responses through QD interaction opens new possibilities for optimizing light utilization in photosynthetic organisms, thereby contributing to enhanced crop yields and more efficient use of light energy in natural and artificial ecosystems.

Edta-assisted rapid synthesis of highly monodisperse and water-soluble ZnSe quantum dots colloids by electron-beam irradiation

ZnSe quantum dots (QDs) have attracted attentions due to small size and strong fluorescence. However, ZnSe QDs are easy to agglomerate and insoluble in aqueous solutions, which limits their practical applications. Herein, we report a novel strategy for synthesizing highly dispersed and water-soluble ZnSe QDs by electron beam radiation with the aid of EDTA within only a few minutes at room temperature without any reduction reagents. In the reaction system, EDTA plays an important role in controlling the quantum size of crystal growth, inhibiting the agglomeration of ZnSe QDs and improving the water solubility. ZnSe QDs exhibit a large bandgap of 4.3 eV, significantly blue shifted compared with bulk ZnSe due to the quantum confinement effect. Constructed the structural model by MS, the nucleation reaction and growth mechanism of ZnSe QDs are proposed. Electron-beam irradiation can be widely used to synthesize water-soluble semiconductor QDs with promising application in biological imaging.

Magnesium Chalcogenide Nanocrystals and Their Core/Shell Nanostructures

AbstractMagnesium chalcogenide with wide bandgap semiconductor is an important candidate for the next generation semiconductor for optoelectronic devices. Colloidal magnesium chalcogenide (MgS, MgSe, and MgTe) nanocrystals are produced with the colloidal method, showing the optoelectronic properties for wide bandgap semiconductors in the violet region. The shape and size of magnesium chalcogenide nanocrystals are precisely controlled via tuning the precursors and ligands. Magnesium chalcogenide are further deposited on ZnSe and ZnS quantum dots for shell materials to enhance fluorescence emission due to the wide bandgap and suitable lattice in magnesium chalcogenide. Magnesium chalcogenide in nanoscale exhibits the potential for wide‐band semiconductors and the shell materials to light‐emitting quantum dots.

Synthesis and optimization of MPA-capped ZnSe quantum dots for photo-activation based applications

Synthesis and optimization of MPA-capped ZnSe quantum dots for photo-activation based applications

Reaction-dependent optical behavior and theoretical perspectives of colloidal ZnSe quantum dots

Colloidal quantum dots (QDs) are attracting research interest because of their unique optical properties that result from the quantum confinement effect. ZnSe QDs, which are II–VI semiconductors, offer a wide direct bandgap (2.7 eV), making them promising for applications such as light-emitting diodes, photodetectors, and biomedical labeling. In the present work, colloidal ZnSe (QDs) were synthesized by the hot-injection method with a Zn:Se ratio of 1:1. The optical properties of ZnSe QDs obtained at different reaction times were investigated by spectrophotometric UV–vis absorption and emission measurements. The as-synthesized ZnSe QDs exhibit blue excitonic emission, and no defect emission was detected. Transmission electron micrographs indicated that the QDs have a spherical morphology with dimensions ranging from 3.69 to 4.53 nm. In particular, the Brus model was applied to demonstrate a correlation between the QD sizes and the optical bandgaps obtained from Tauc plots.

Enhanced luminescence using the core‐shell‐shell structure of 3‐mercaptopropionic acid‐capped ZnSe/ZnS: Mn/ZnS quantum dot

AbstractIn this study, we used the surface stabilizer 3‐mercaptopropionic acid (MPA) to synthesize ZnSe quantum dots in nontoxic aqueous solvents. Because of the –COOH group, MPA is an SH‐R‐COOH molecule that is added to improve the dispersion and quantum dot (QD) compatibility with antibodies. The different structures ZnSe, Mn‐doped ZnSe, Mn‐doped ZnSe/ZnS, and ZnSe/Mn‐doped ZnS/ZnS were investigated to find the optimum photoluminescence (PL). The structure and distribution element of ZnSe/Mn‐doped ZnS/ZnS QD were analyzed by the high‐resolution TEM image and scanning transmission electron microscopy. This finding of the ZnS buffer layer helps to reduce the defect lattice of QDs, which increases PL significantly. The highest PL intensity of ZnSe/ZnS:Mn/ZnS is significantly more than that of ZnSe and ZnSe/ZnS 6.2 and 3.3 times, respectively. In addition, the fluorescence efficiency of ZnSe/ZnS:5%Mn/ZnS‐MPA was 74.37% higher than that of ZnSe:5%Mn/ZnS‐MPA (55.04%) in ZnS buffer.

Zinc selenide quantum dots as fluorescent labels for biomedical imaging

We, herein, report a facile green synthetic route for the gram‐scale synthesis of high‐quality thiol‐derivatized zinc selenide quantum dots (QDs) using selenourea as the source of selenium at a relatively low temperature. The one‐pot synthesis of colloidal dots has been achieved by selenizing zinc (II) acetate in a non‐coordinating solvent medium. The structural, microstructural, optical, thermal, textural and electronic properties of the as‐synthesized monodisperse ZnSe dots have been investigated in detail. We attribute the observed green emission from the dots to the donor‐acceptor pair (DAP) recombination of photoexcited charge carriers. All the findings of the investigation indicate that ZnSe QDs hold great promise as a nanoscale emissive probe to unveil cellular dynamics beyond the capabilities of conventional imaging techniques.

Applications of ZnSe quantum dots for solar energy harvesting

To reduce the large usage of fossil fuels, scholars have made great efforts to develop green energy such as wind energy, biomass energy, and solar energy. Solar energy has special benefits, thus solar energy harvesting technologies including solar cells, luminescent solar concentrators, photocatalysis have been studied widely. It is meaningful to study the working principle of those technologies. For the special properties of ZnSe, different kinds of nanostructure of it have been used for solar energy harvesting. Among them, since quantum qot structure has some specific characters, the application of it for solar energy harvesting are worthwhile to mention. This study aims to introduce solar cells, luminescent solar concentrators, photocatalysis technologies and the applications of ZnSe quantum dots for them. It found that ZnSe quantum dots enhanced the behavior of Si nanowire solar cells. Besides, the outstanding performance of luminescent solar concentrators based on InP/ZnSe quantum dots is partly own to ZnSe shell structure. Moreover, some quantum dots including ZnSe shell structure behave good photocatalytic H2 evolution performances. At the same time, the nanostructures of the quantum dots mentioned are shown.

The role of surface functionalization in quantum dot-based photocatalytic CO2 reduction: balancing efficiency and stability.

Photocatalytic CO2 reduction offers a promising strategy to produce hydrocarbons without reliance on fossil fuels. Visible light-absorbing colloidal nanomaterials composed of earth-abundant metals suspended in aqueous media are particularly attractive owing to their low-cost, ease of separation, and highly modifiable surfaces. The current study explores such a system by employing water-soluble ZnSe quantum dots and a Co-based molecular catalyst. Water solubilization of the quantum dots is achieved with either carboxylate (3-mercaptopropionic acid) or ammonium (2-aminoethanethiol) functionalized ligands to produce nanoparticles with either negatively or positively-charged surfaces. Photocatalysis experiments are performed to compare the effectiveness of these two surface functionalization strategies on CO2 reduction and ultrafast spectroscopy is used to reveal the underlying photoexcited charge dynamics. We find that the positively-charged quantum dots can support sub-picosecond electron transfer to the carboxylate-based molecular catalyst and also produce >30% selectivity for CO and >170 mmolCO gZnSe-1. However, aggregation reduces activity in approximately one day. In contrast, the negatively-charged quantum dots exhibit >10 ps electron transfer and substantially lower CO selectivity, but they are colloidally stable for days. These results highlight the importance of the quantum dot-catalyst interaction for CO2 reduction. Furthermore, multi-dentate catalyst molecules create a trade-off between photocatalytic efficiency from strong interactions and deleterious aggregation of quantum dot-catalyst assemblies.

Molecular Additive-Assisted Tellurium Homogenization in ZnSeTe Quantum Dots.

The addition of aqueous hydrohalic acids (HX, X = F, Cl, Br) during the synthesis of colloidal quantum dots (QDs) is now widely employed to achieve high-quality QDs. However, this reliance on the use of aqueous solutions is incompatible with oxygen- and water-sensitive precursors such as those used in the synthesis of Te-alloyed ZnSe QDs. Herein, we show this incompatibility, leads to phase segregation into Te-rich and Te-poor regions, causing spectral broadening and luminescence peak shifting under high laser irradiation and applied electrical bias. Here we report a synthetic strategy to produce anhydrous-HF in-situ by using benzenecarbonyl fluoride (BF) as a chemical additive. Through in-situ 19 F nuclear magnetic resonance spectroscopy, we find that BF reacts with surfactants in tandem, ultimately producing intermediary F···H···trioctylamine adducts. These act as a pseudo-HF source that releases anhydrous HF. The controlled release of HF during the nucleation and growth steps homogenizes the Te distribution in the ZnSeTe lattice, leading to spectrally-stable blue-emitting QDs under increasing laser flux from ∼3 μW to ∼12mW and applied bias from 2.6 to 10V. Single-dot photoluminescence (PL) spectroscopy and analyses of the absorption, PL and transient absorption spectra together with density functional theory point to the role of anhydrous HF as a Te homogenizer. This article is protected by copyright. All rights reserved.

UV Light as an Efficient Tool for Reducing Surface Defects of ZnSe-MSA Quantum Dots.

Defects in ZnSe quantum dots are responsible for increasing the trap states, which can lead to the drastic reduction of their fluorescence output, being one of the major drawbacks of these materials. As surface atoms become more relevant in these nanoscale structures, energy traps due to surface vacancies, play a very definite role in the final emission quantum yield. In the present study, we report the use of photoactivation procedures to decrease surface defects of ZnSe QDs stabilized with mercaptosuccinic acid (MSA), in order to improve the radiative pathways. We applied the colloidal precipitation procedure in a hydrophilic medium and evaluated the role of Zn/Se molar ratios as well as the Zn2+ precursors (nitrate and chloride salts) on their optical properties. Best results (i.e. increment of 400% of the final fluorescence intensity) were obtained for nitrate precursor and a Zn/Se = 1.2 ratio. Thus, we suggest that the chloride ions may compete more efficiently than nitrate ions with MSA molecules decreasing the passivation capability of this molecule. The improvement in ZnSe QDs fluorescence can potentialize their use for biomedical applications.

Study Using the Brus Equation to Examine How Quantum Confinement Energy Affects the Optical Characteristics of Cadmium Sulfide and Zinc Selenide

In this paper, the Brus equation was used to study the effects of quantum confinement energy on the optical properties of material with quantum dot (QD). It was found that the wavelength and energy gap depend on the quantum confinement energy. With the increase in the energy of quantum confinement, the energy gap increases and the absorption wavelength decreases and shifts toward the UV region. This large blue shift observed in CdS and ZnSe QDs could be exploited for the potential applications as smart materials in photonic nanodevice and various other applications.

Photoluminescence from Cu / Mn: ZnSe quantum dots and their phase transformation in silicate glass

To realize the polychromatic and tunable luminescence of ZnSe quantum dots (QDs) in glass, Cu and Mn co-doped ZnSe QDs (Cu/Mn: ZnSe QDs) glass were prepared by melt quenching and subsequent heat treatment method. For the ZnSe QDs glass without Cu and Mn dopants, there is only intrinsic luminescence from ZnSe QDs observed. For Cu/Mn: ZnSe QDs glass, the band edge emission from ZnSe QDs is quenched and the broadband emission from Cu2+/Mn2+ ions is observed, which is resulted by the effective energy transfer from ZnSe QDs to Cu2+/Mn2+ ions. With the increase of heating temperature, the emission spectra of Cu/Mn: ZnSe QDs glass change from green to orange light, which is characteristic luminescence wavelengths of Cu2+ and Mn2+ ions, respectively. For the ZnSe QDs glass without Cu2+ and Mn2+ dopants, ZnSe QDs undergo a phase transformation from the cubic to the hexagonal structure at higher heating temperature (≥610 °C) than those of Cu/Mn: ZnSe QDs glass at 600 °C and Cu-doped ZnSe QDs glass at 580 °C, in addition, For Cu/Mn: ZnSe QDs glass, the phase transformation temperature drops to 600 °C. For Cu-doped ZnSe QDs glass, the phase transformation temperature is further reduced to 580 °C. However, for Mn-doped ZnSe QDs glass, there is no phase transformation. It indicated that Cu2+ promotes the phase transformation of ZnSe QDs.

Advances in Solution-Processed Blue Quantum Dot Light-Emitting Diodes.

Quantum dot light-emitting diodes (QLEDs) have been identified as a next-generation display technology owing to their low-cost manufacturing, wide color gamut, and electrically driven self-emission properties. However, the efficiency and stability of blue QLEDs still pose a significant challenge, limiting their production and potential application. This review aims to analyse the factors leading to the failure of blue QLEDs and presents a roadmap to accelerate their development based on the progress made in the synthesis of II-VI (CdSe, ZnSe) quantum dots (QDs), III-V (InP) QDs, carbon dots, and perovskite QDs. The proposed analysis will include discussions on material synthesis, core-shell structures, ligand interactions, and device fabrication, providing a comprehensive overview of these materials and their development.

Effect of thermal treatment on ZnSe quantum dots and energy transfer in borosilicate glasses doped with ZnSe and Er3+/ZnSe

This study assessed the effect of heat treatment on the spectroscopic properties of borosilicate glasses doped with ZnSe quantum dots (QDs) and co-doped with Er3+/ZnSe. The gradual growth of ZnSe QDs upon heat treatment was probed by TEM. The emission intensity of ZnSe-doped glasses rapidly increased up to 20 h of heat treatment because of the formation and development of ZnSe QDs, then gradually decreased due to the rise in non-radiative loss between the enlarged particles. With increasing number of ZnSe QDs, the energy transfer from QDs to Er3+ ions became prominent in Er3+/ZnSe-co-doped glasses, showing enhanced emission up to 20 h of heat treatment. The excited state 4S3/2 lifetime values, increased with heat treatment, whereas an opposite trend was observed for the lifetime values of state 4I13/2, indicating a possible participation of the ZnSe QDs in facilitating the energy migration mechanism through the 4I13/2 level, followed by non-radiative decay.

Synthesis of I@MPA-Mn:ZnSe as an efficient contrast agent for CT/fluorescence bi-modal imaging application

Bi-modal imaging contrast agent has attracted considerable attention in medical physics research field via quantum dots (QDs) fabrications. Doped quantum dots are playing an important role in seeking alternatives to conventional heavy metal-containing particles for medical applications. In order to improve imaging diagnosis, herein we report the design and synthesis of I@MPA-Mn:ZnSe as an efficient contrast agent. The medium, mercaptopropionic acid (MPA) capped Mn:ZnSe QDs surface-conjugated with a commercial contrast agent (Iohexol), was synthesized in seeking to overcome the limitations of Iohexol, also towards advancing bi-modal imaging approaches. In this study, morphology, elemental, absorption and fluorescence analysis were investigated, followed by a preliminary study of CT contrast enhancement and cell viability. In comparison to Iohexol, the fluorescence of I@MPA-Mn:ZnSe is observed at 585 nm. The CT Hounsfield unit (HU) increases linearly with mass concentration, with a four-fold increment in HU over that of Iohexol, producing greater than 328 ΔHU at similar concentrations, confirming the CT contrast efficiency of I@MPA-Mn:ZnSe. Cytotoxicity studies have confirmed that the medium possesses good biocompatibility and low toxicity to cells (HepG2 and MDA-MB-321). Present results for CT enhancement and brightness of fluorescence of I@MPA-Mn:ZnSe point to its great potential as a bi-modal contrast medium for further diagnosis applications.

Highly stable water-soluble ZnSe:Cu quantum dots coated with doubly ZnS shell

Doped ZnSe quantum dots (QDs) have become a potential substitute for Cd-based QDs. In this paper, center-doped monodisperse Cu-doped ZnSe (ZnSe:Cu) QDs are synthesized as the first step in aqueous solution by co-nucleation doping method, and then the double-layered ZnS shell is grown by successive growth. The prepared ZnSe:Cu/ZnS/ZnS QDs have high photoluminescence(PL) intensity and excellent stability in the blue region. The crystal structure has not been changed and the PL intensity maintains 95% after 365 days stored in the air. The outstanding performance of the prepared QDs benefit from the ZnS shell grown outside the core of ZnSe:Cu, especially the second layer of the ZnS shell can effectively limit excitons and Cu in the ZnSe core and isolate O2. The strategy in our work paves a new path to elevate the stability of QDs.

Efficient photoluminescence from Cu2+ doped ZnSe/ZnS core-shell quantum dots in silicate glass

As a nontoxic and harmless photoelectric material, ZnSe quantum dots (QDs) have a broad application prospect. Incorporation of ZnSe QDs into glass provides a stable and robust substrate for QDs, but the low fluorescence efficiency of ZnSe QDs in glass limits their application. In this work, ZnSe/ZnS core-shell structure QDs is prepared in silicate glass by melt quenching and subsequent heat treatment, which is evidenced by XRD, TEM and Raman results. The surface defects of ZnSe QDs are passivated by the ZnS shell, which enhanced the luminescence of ZnSe QDS and increased the PL quauntum yeilds (PLQY) to 1.2%. With the introduction of Cu2+, two PL spectra around 500 nm and 650 nm appear simultaneously. The PL spectrum at 500 nm shows obvious size dependence, which is due to the energy transfer between ZnSe QDs and the D orbital of Cu2+, while the spectrum at 650 nm is attributed to a deeper defect. With the increase of heat treatment temperature and Cu2+ concentration, the defect luminescence gradually weakened and PLQY further increased to 4.62%.

Arrays of size-dispersed ZnSe quantum dots as artificial antennas: Role of quasi-coherent regime and in-gap states of excitons for enhanced light harvesting and energy transfer

Densely packed thin films of semiconductor quantum dots (QDs) shows specific the optoelectronic properties originate from the QDs coupling that may pave the way for new controllable building blocks for quantum technologies and light-harvesting complexes in natural photosynthetic systems and photovoltaic cells. In this work we were compared the optical properties and an excitonic energy transfer (EET) process in an aqueous solutions and dense packed films of ZnSe QDs with a narrow size distribution. An unexpectedly large nonlinear increase in the photoluminescence (PL) intensity was detected in QDs films with the decrease of an excitation energy that can be explained by resonantly transferred of EET through the quantum states. We found that with decreasing of the excitation energy form of quasi-coherent regime of excitons and the quantum and surface PL emission increases by a factor ∼10 and ∼6, respectively, due to increasing the EET rate.

Highly sensitive and selective microRNA photoelectrochemical assay with magnetic electron donor–acceptor covalent organic framework as photoactive material and ZnSe QDs as photocurrent-polarity-switching factor

Herein, taking microRNA-138 (miRNA-138) as a model due to its important role in pre-diagnosis and therapy of Alzheimer's disease, a highly sensitive and selective photoelectrochemical (PEC) sensor was developed based on the magnetic electron donor–acceptor (D–A) covalent organic framework (COF), Fe3O4 @D–A COF, as the photoactive material and ZnSe quantum dots (QDs) as the photocurrent-polarity-switching factor. Fe3O4 @D–A COF, which contained the structure of D–A with a fast separation and transportation of photogenerated carriers, showed a large cathodic photocurrent. ZnSe QDs, as a photosensitive material, matched with D–A COF in energy level and could change the photocurrent polarity of D–A COF. Finally, the obtained Fe3O4 @D–A COF-hairpin DNA1/ZnSe QDs-hairpin DNA2 complex, which was formed through the miR-138-induced catalytic hairpin assembly (CHA) reaction, was adsorbed magnetically on the surface of the magnetic indium tin oxide electrode, producing a large anodic photocurrent. Based on the CHA reaction amplification, magnetic separation, D–A structure of COF and photocurrent-polarity-switching strategy, miRNA-138 was selectively and sensitively assayed (linear range, 1 fM to 10 nM; detection limit, 45 aM). The proposed sensor shows its great prospects in clinical analysis and early diagnosis of disease.