ZnSe Quantum Dots Research Articles

Rapid ratiometric detection of Cd2+ based on the formation of ZnSe/CdS quantum dots.

Developing simple and sensitive non-aggregation strategy for detecting Cd2+ is necessary for improving the selectivity and sensitivity of probe. Here, we establish a simple, rapid and ratiometric strategy for the recognition of Cd2+ based on the formation of core-shell ZnSe/CdS structure using ZnSe quantum dots (QDs). The transformation from binary ZnSe QDs to core-shell ZnSe/CdS QDs both change the elemental composition and structure of ZnSe QDs, leading to the changes in band gap of ZnSe QDs, which could be observed in the UV-vis spectra. In the detection process, ZnSe QDs only possess absorption peak at 343 nm, the formation of ZnSe/CdS after the addition of Cd2+ leads to the appearance of the new peak at 397 nm, while other heavy metal ions could not cause the appearance of new absorption peak. Therefore, this strategy shows good selectivity for Cd2+ detection. Based on this strategy, the limit of detection (LOD) for Cd2+ is 11 nM by UV-vis spectroscopy with a desirable relation of linearity (R2 = 0.999) between A397/A343 and Cd2+ contents, which is superior to the LOD of most reported nanomaterials. The response time for Cd2+ detection is as short as 60 s, which is suitable for rapid detection. This ratiometric probe has also been applied to the detection of Cd2+ in tap water samples, the recovery of Cd2+ was between 94.9% and 105.6% for tap water samples, indicating the high accuracy of our ratiometric assay. Our strategy not only provided a new method for detecting Cd2+, but also put forward an implication that the band energy changes of QDs caused by heavy metal ions can be applied in the selective and sensitive detection of heavy metal ions.

Facile synthesis and color conversion of Cu-doped ZnSe quantum dots in an aqueous solution

A facile growth-doping method in aqueous solution has been developed to synthesize Cu-doped ZnSe (ZnSe:Cu) QDs by using thioglycolic acid (TGA) as a stabilizer. The effects of the Cu doping concentration, reaction temperature and pH value on the synthesis of ZnSe:Cu QDs were investigated systematically. The as-synthesized ZnSe:Cu QDs with an excellent green emission still belong to a cubic zinc blende crystalline structure, and the average particle size is approximately 3.0 nm. The photoluminescent quantum yield (PLQY) is as high as 20%, and the exciton radiative lifetime is approximately 113.8 ns. Moreover, the patterned ZnSe:Cu QDs thin films have been successfully fabricated by using an inkjet printing method to verify the ability of the potential application to the color conversion. With the assistance of 5.5 pair distributed bragg reflector (DBR) structures, the color coordinate of the ZnSe:Cu QDs thin film excited by the blue LEDs is located at (0.2182, 0.4352) and the intensity of PL peak located at 513 nm reaches to be 45.1%. In addition, the PLQY of color conversion-based ZnSe:Cu QDs thin film is approximately 9.64%. Based on these results, ZnSe:Cu QDs are potentially useful for the fabrication of optoelectronic devices, especially QDs photoluminescence and electroluminescence.

Synthetic development in Cd–Zn–Se quantum dots chemistry

Despite a great number of studies devoted to the synthesis of chalcogenide quantum dots (QDs), many essential questions remain open up to date. Primarily, it is a safety of the synthesis, both in the laboratory and in the industry. Another issue is the reproducibility of QDs with desired characteristics. And, without doubt, the ability to adjust properties of the resulting QDs by the implementation of various approaches to the synthesis is significant. Here we provide a novel approach to the synthesis of ternary Cd–Zn–Se QDs (ratios Cd: Zn = 10 : 90; 25 : 75; 50 : 50; 75 : 25; 90 : 10) using disubstituted selenourea as a novel source of selenium. (Z)-1-hexyl-3-(octadec-9-enyl)selenourea was synthesized in three steps with a good yield of the final product. It opens up a simple, convenient and environmentally friendly way to the synthesis of the selected QDs. Varying the molar ratios of Cd and Zn, QDs of different composition were produced in high yields. According to the conducted research, highly photoluminescent ternary Cd–Zn–Se QDs (photoluminescent quantum yield PL QY up to 64%) are uniform, both in elemental composition and in size (3.6–5.3 nm). Moreover, the selection of given selenourea made it possible to scale the synthesis by 24 times with an increase in the amount of QDs without loss of product quality. This demonstrates the feasibility to produce such type of materials on an industrial scale.

Tuning of emission from copper-doped ZnSe quantum dots

In this paper, different concentrations of copper-doped zinc selenide quantum dots (Cu:ZnSe QDs) were synthesized and compared with differently sized (2.0–3.7 nm) Cu:ZnSe QDs by keeping the concentration of Cu fixed at 5%. In both cases a high-temperature wet chemical route was employed for synthesis. As the concentration of Cu increased from 2.5% to 12.5% in the solution, a clear redshift was observed in the absorption spectrum, which is an indication that Cu ions have been incorporated into the host lattice. In order to identify the state in which the Cu ions are present, electron paramagnetic resonance (EPR) studies were carried out on the samples. The EPR spectra reveal a resonance signal which is characteristic of Cu2+ ions. With an increase in concentration of Cu ions it is found that the component increases. Photoluminescence emission and excitation studies revealed both band-edge and Cu-related emission, further strengthening the incorporation of Cu ions in the host lattice.

Serial dilution bioassay for the detection of antibacterial potential of ZnSe quantum dots and their Fourier transform infra-red spectroscopy

The aim of this work lies in synthesize of ZnSe nanoparticles (quantum dots: QDs) by microwave (MW) irradiation-assisted method; this method can provide the reduced-dimension particles having high quantum confinements. The Cu-doped and undoped ZnSe QDs were synthesized at the presence of mercaptoacetic acid (MAA) capping agent at different physical-chemical conditions of pH-end (8.0, 10.2, 11.2 and 12.2) of suspension solution, different MW irradiation times (MWIRT = 0, 1, 2, 3, 4 and 6 min) and also at different Cu concentrations (0, 0.1, 0.75, and 1.5 mol%); so, produced QDs were characterized structurally employing Fourier transform infra-red spectroscopy (FTIR) to complete previously published results on their X-ray diffraction (XRD) and UV–Visible spectroscopy. Also, serial dilution bioassay was performed against both gram positive and gram negative bacteria to assess their antibacterial activity; for the antibacterial experiments, four Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus bacteria were used as test strains. Results show that these QDs are as potential and promising antibacterial agents, with a dominant (optimal) activity in the cases of (pH = 10.2, MWIRT = 0 min), (pH = 12.2, MWIRT = 0 min; and pH = 11.2, Cu dopant = 1.5%) and (pH = 11.2, MWIRT = 4 min) for Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus, respectively. Minimum inhibitory concentration (MIC) results suggest them as novel class of bio-agents. The studied ZnSe QDs had a size of about ∼2 nm and MIC of about 3 ppm for all tested samples. All samples have the same minimum bactericidal concentration (MBC) as MIC, indicating both inhibition and killing of microorganisms. To draw inference about the prominent bio-activity of ZnSe QDs, they should be synthesized in nano-scale, in which effectively enable them to penetrate to the cell walls of both gram-negative and gram-positive bacteria. The FTIR absorption peaks for the synthesized samples, confirm the formation of ZnSe structure, justifying the previously reported results of XRD, field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX); so, the interaction between Se2− and Zn2+ ions were confirmed via FTIR analysis.

Ligand-assisted synthesis and cytotoxicity of ZnSe quantum dots stabilized by N-(2-carboxyethyl)chitosans

Here we report a green synthesis of ZnSe quantum dots (QDs) in aqueous solution of polyampholyte chitosan derivative – N-(2-carboxyethyl)chitosan (CEC) with substitution degrees (DS) from 0.7 to 1.3 and molecular weight (MW) of 40 kDa and 150 kDa. We have shown that the maximum intensity of photoluminescence (PL) is exhibited by ZnSe QDs synthesized in solutions of CEC with DS 1 at Se:Zn molar ratio 1:2.5. The defect-related band was predominant in the PL spectra of ZnSe QDs obtained at room temperature; however, hydrothermal treatment at 80–150 °C during 1–2 h significantly increased contribution of exciton emission to the spectra. Cytotoxicity of ZnSe QDs was investigated by MTT assay using cancer cell lines SKOV-3; SkBr-3; PANC-1; Colon-26 and human embryonic kidney cell line HEK293. Cytotoxicity of ZnSe QDs did not depend on MW or DS of CEC but significantly depended on the cell line, being the lowest for normal human cells HEK293 and breast cancer cell line SKOV-3. The hydrothermally treated ZnSe QDs showed higher toxicity toward both normal and cancer cell lines. Since ZnSe QDs were toxic for most of the investigated cancer cell lines, they cannot be used as inert tracers for bioimaging, but can be promising for further investigation for anticancer therapy.

Synthesis and dual-channel optical properties of Mn-doped ZnSe quantum dots

We have successfully demonstrated the colloidal hot-injection process to easily obtain the Mn-doped ZnSe quantum dots (QDs) with a size of about 4–5 nm, and d-spacing is 0.31 nm, corresponding to the (1 1 1) lattice plane of ZnSe. Experimental results show that UV–vis absorption and fluorescence spectra were recorded to elucidate the role of Mn2+ ions substituted into ZnSe, which resulted in the carrier transfer of luminescent sites by a small amount of Mn2+ dopant. The small size of the Mn-doped ZnSe QDs offers intriguing opportunities for their application in photonic, bioimaging, and spintronics devices.

Influence of a Capping Ligand on the Band Gap and Excitonic Levels in Colloidal Solutions and Films of ZnSe Quantum Dots

Semiconductor quantum dots are promising nanostructures for their application in solar cells of the 3rd generation, photodetectors, light emitting diodes, and as biological markers. However, the issue concerning the influence of superficial organic stabilizers (ligands) on the energy of excitons in quantum dots still remains open. In this work, by analyzing the optical spectra of colloidal solutions and films of ZnSe quantum dots stabilized with 1-thioglycerol, it is found that the energy of excitons and their migration depend not only on the quantum confinement effect, but also on the superficial contribution from the thiol stabilizer group –SH. The dependence of the exciton energy in ZnSe quantum dots on the surface stabilizer concentration is experimentally revealed for the first time. The short size of the stabilizer molecular chain and the large initial energy of excitons are shown to result in the effective migration of excitons over an array of quantum dots.

Thioglycolic acid-capped ZnSe quantum dots as nanoprobe for cobalt(II) and iron(III) via measurement of grey level, UV-vis spectra and dynamic light scattering.

Thioglycolic acid-functionalized ZnSe quantum dots (QDs) as a colorimetricnanoprobe were prepared and applied to the determination of cobalt(II) and iron(III). Test strips were obtained by a dipping-drying process. On exposure to Co(II), they undergo a color change from white to brown, and on exposure to Fe(III) from white to pink. The limits of detection (LOD) are 2.6mgL-1 for Co(II) and 2.2mgL-1 for Fe(III). Test strips introduce a low-cost, portable, rapid and convenient tool for determination of Co(II) and Fe(III). In addition, two other analytical methods have been studied for detection of Co(II) and Fe(III) at low concentration. The first is UV-vis spectrometry which has a LOD as low as 0.14mgL-1 for Co(II) (at 412nm) and 0.12mgL-1 for Fe(III) (at 400nm). The second is dynamic light scattering (DLS) with a LOD of 3.0μgL-1 for Co(II) and 2.5μgL-1 for Fe(III). Graphical abstract Thioglycolic acid-functionalized ZnSe quantum dots (TGA-ZnSe QDs) show high sensitivity and low detection limits for Co2+ and Fe3+.

Preparation of ZnSe Quantum Dots by Hydrothermal Method Assisted by Ammonia

ZnSe quantum dots (QDs) with high intrinsic fluorescence quantum efficiency (QY) and low defect luminescence were prepared by hydrothermal method assisted with ammonia, in which the selenium powder and zinc acetate were used as Se and Zn source, and the mercaptopropionic acid (MPA) was used as ligand. Effect of ammonia amount, Zn/Se ratio, Zn/MPA ratio, and reaction time was investigated in detail in this study. The as-prepared ZnSe QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption spectrum (UV-Vis), fluorescence spectrum (PL). ZnSe QDs assisted with ammonia were sphalerite, and with emission peak in the range of 380~405nm. The optimal condition was following: Zn/Se ratio was 5, Zn/MPA ration was 0.25, reaction temperature was 110 °C and reaction time was 6 h. Under the optimal condition, ZnSe QDs with intrinsic emission QY of 47% and diameter of 3.8±0.3 nm can be obtained. The ZnSe QDs prepared in this study were expected to replace toxic Cd-related QDs in biomarkers, violet and blue light solid luminescent devices, and provide excellent parent materials for the doped ZnSe QDs system.

Influence of Germanium and Zinc Selenium Nanocrystals on the Photoelectric Properties of the n-GaAs – p-(GaAs)0.69(Ge2)0.17(ZnSe)0.14 Heterostructure

The article determines the technological conditions of growing the films of solid solution (GaAs)1-x-y(Ge2)x(ZnSe)y on GaAs substrates by the method of liquid phase epitaxy from the tin melt-solution. The grown epitaxial films had the thickness of ~ 10 μm, n -type conductivity with specific resistances of ~ 0.1 Ωˑcm and the current carrier concentration of 5.1ˑ1017 cm-3. Spectral photosensitivity of n-GaAs – p-(GaAs)0.69(Ge2)0.17(ZnSe)0.14heterostructureshave been studied and two distinct peaks corresponding to Ge nanocrystals with GaAs molecule compounds and ZnSe quantum dots have been detected. It is shown that the photosensitivity spectrum of the studied solid solution has six Gaussian components which correspond to the pair atoms of Ge2 and compounds AsGe, GaGe, GeSe, AsZn, GaSe and ZnSe. The spatial configurations of tetrahedral bonds within nanoclusters formed by Ge and ZnSe impurities based on a GaAs unit cell are presented. It is also determined that the nanoclusters in the solid solution (GaAs)1-x(Ge2)x consist of three As atoms, two Ge atoms and three Ga atoms. Since the unit cell of the lattice with the diamond-like structure consists of eight atoms, the linear dimensions of the nanocluster are 5.6, 5.6, 5.6 A. In the nanocluster in the solid solution (GaAs)1-x-y(Ge2)x(ZnSe)y formed by the GaAs molecule, ZnSe and the Ge2 pair atoms contains 14 atoms: five As atoms, two Ge atoms, one Se atom, one Zn atom, and five Ga atoms. So the As and Ga atoms are bound through the Ge, Zn, and Se atoms, and therefore the linear dimensions of the nanoclusters become 5.6; 5.6; 10 A. Thus, the matrix lattice consists of GaAs molecules and twin Ge atoms, and ZnSe molecules are located on their surface defective regions. Since zinc selenide molecules and germanium selenide compounds form three acceptor levels in the GaAs valence band, and the ZnSe lattice parameter is slightly larger than the matrix lattice, at ZnSe locations, the lattice microdistortions are observed and they have an increased potential which promotes the formation of ZnSe nanocrystals.

Temperature dependence of photoluminescence properties of water-soluble ZnSe quantum dots

We have investigated the optical properties of ZnSe quantum dots (QDs) prepared by a hydrothermal method. The photoluminescence (PL)-decay profiles become slower with an increase in temperature up to 160 K, contrary to an ordinary behaviour due to thermal quenching. The temperature dependence of the PL-decay profile is explained by a three-state model consisting of a ground state and two excited states of the lower-lying bound-exciton and higher-lying dark-exciton states. The analysis of the temperature dependence of the decay time indicates that the dark-exciton state contributes to the PL-decay process in the ZnSe QDs.

Preparation of ZnSe-ZnS alloy quantum dots by a hydrothermal method and their optical properties

We prepared colloidal ZnSexS1−x alloy quantum dots (QDs) and investigated their optical properties. ZnSexS1−x QDs were successfully prepared by a hydrothermal method, which was confirmed by the results of X-ray structural analysis. When the alloy composition was decreased from x = 1 to 0, the absorption energy continuously shifted to the high energy side. Band-edge photoluminescence (PL) was the main PL band in ZnSe QDs, whereas only defect - related PL band was observed in ZnS QDs. The band-edge PL was clearly observed as the main PL band for x = 0.52 to 1, which shifted to the high energy side by decreasing x.

Investigation of the effect of Sr-doped in ZnSe layers to improve photovoltaic characteristics of ZnSe/CdS/CdSe/ZnSe quantum dot sensitized solar cells

In this work, QDSSCs were synthesized based on CdS/CdSe QDs with two ZnSe layers and we investigated the effect of alkaline earth metal ions (such as: Mg2+, Ca2+, Sr2+, Ba2+) dopants in outer ZnSe passivation layer to improve the photovoltaic performance in QDSSCs. Amongst different metal ions, Sr2+ doped ZnSe passivation layer obtained the best PCE comparing to plain ZnSe passivation layer. Then, at the following, we investigated the effect of Sr2+ ions doped in two ZnSe layers: the inner, the outer and each two layers simultaneously. The cell devices were prepared using photoanodes with different configurations, polysulfide electrolyte and Cu2S/Brass foil counter electrode. Photovoltaic measurement results represent that Sr2+ ions doped in two ZnSe layers assist to a notable improvement in the photocurrent, photovoltage and power conversion efficiency of the resultant cell device in comparison with a plain ZnSe layers and show the best performance between all studied cell devices with a solar PCE of 4.10% under one full sun illumination. The results of impedance spectroscopy (IS) show that doping of Sr2+ ions in both of the ZnSe layers increase the photogenerated electron lifetime and better transport electron and hole in the photoanode comparing to plain ZnSe treated photoanode.

A review on the progress of ZnSe as inorganic scintillator

• Fundamentals of scintillation in inorganic scintillators. • Properties of common inorganic scintillators and discussion of investigations on ZnSe based scintillators. • Factors affecting scintillation performance of ZnSe based scintillators. • Basics of quantum dots, efforts taken for synthesis of ZnSe quantum dots and advantages of ZnSe quantum dot scintillators. Modern scintillator detectors act as an efficient tool for detection and measurement of ionizing radiations. ZnSe based materials have been found to be a promising candidate for scintillation applications. These scintillators show much-needed scintillation efficiency along with advantages such as high thermal and radiation stability, less-toxicity, non-hygroscopicity, emissions in the visible range and small decay time etc. Further, in quantum confinement regime, they show improvement in luminescent properties and size dependent emissions. In this review article, the attempt has been made to trace the progress of ZnSe based materials towards highly efficient quantum dot scintillators. Here, the fundamental process of scintillation has been explained. Factors such as doping, annealing, heavy ion irradiation which affects the scintillation response of ZnSe based scintillators have also been discussed. Method of synthesis plays a key role in optimization of quantum dot properties. Hence, it has been tried to trace the development in methods of synthesis of quantum dots. With optimized synthesis, we can extend applications of these highly efficient quantum dot scintillators for various scientific and industrial applications.

PH-, microwave irradiation time-, and dopant content- sensitive photoluminescence of pure and Cu-doped ZnSe quantum dots fabricated by rapid microwave activated method

Synthesis and photoluminescence (PL) of colloidal MAA-capped ZnSe and ZnSe:Cu quantum dots (QDs) is investigated here. The size of QDs is varied tunably by changing the pH, MWIR time and Cu dopant percentage. Results show that the as-synthesized ZnSe QDs and doped QDs (dQDs) have similar cubic zinc blend structure. PL properties is synthesis condition-sensitive in which can be controlled by them, suggesting applications in bio-sensors. It was founded that, PL peak positions had red shift and PL intensities increase commonly as pH increases for different MWIR times; relatively such trend could be observed with increase of Cu dopant. It is suggested that MAA dissociates from the ZnSe outer shell at higher pH, resulting in aggregation and loss of solubility and can change the fluorescence of the MAA-capped QDs. Also, Cu ions as doping agent may be the centers of energy transfer role in the lattice. Generally, PL intensity increases slightly by increasing in pH, and MW irradiation time. Linear decremental, non-linear variation, and nonlinear decremental trends of optical gap were identified at different mentioned synthesis conditions, correspondingly. In brief, the studied QDs promises a novel range of green-emission luminescent QDs for development of nano-probes in bio-imaging applications.

Hydrothermal synthesis of ZnSe:Mn quantum dots and their optical properties

Water-soluble Mn2+-doped ZnSe quantum dots (QDs) were synthesized using a hydrothermal method. The characteristics of the precursor solutions greatly affected the photoluminescence (PL) properties of the ZnSe:Mn QDs. In QDs synthesized with alkaline precursor solutions, a PL band originating from the intra-3d shell transition of Mn2+ is clearly observed, indicating that Mn2+ ions are thoroughly doped inside the ZnSe QDs. The PL quantum yield of the ZnSe:Mn QDs synthesized under the optimum conditions reached 20%. By introducing a ZnS shell at the surface of the ZnS:Mn QDs, the PL properties were improved and the PL quantum yield was further increased to 30%.

Ultrasensitive electrochemiluminescence biosensor for dopamine based on ZnSe, graphene oxide@multi walled carbon nanotube and Ru(bpy)32+

A ultrasensitive electrochemiluminescence (ECL) biosensor was designed for the detection of dopamine using ZnSe quantum dots and Ru(bpy)32+ as the signal probes, and graphite oxide and multi-walled carbon nanotube as the supporting matrix. The biosensor exhibits efficient and stable anodic ECL signal (at 1.10 V vs. Ag/AgCl) in phosphate buffer solution (pH 9.0) containing Tripropyl amine. The ECL emission decreases with adding dopamine, which can be attributed to the quenching effect from interaction between ZnSe and dopamine. The possible reaction mechanism of the ECL system is studied, and a method for the determination of dopamine is proposed. Under the optimal experimental conditions, the ECL emission decreases linearly with the logarithm of dopamine concentration in a wide linear range from1 × 10−9 to 1 × 10-5 mol L−1 with a detection limit of 6 × 10-10 mol L-1 (S/N = 3). The biosensor is also successfully applied to detect dopamine in human blood serum samples.

Quantum Dot Doping-Induced Photoluminescence for Facile, Label-Free, and Sensitive Pyrophosphatase Activity Assay and Inhibitor Screening.

Development of simple, convenient, and sensitive assay methods for pyrophosphatase (PPase) activity is of importance, for disease diagnosis and drug discovery. Herein, a simple, rapid, label-free, and sensitive fluorescence sensor for PPase activity assay is developed, using Cu2+ doping-induced quantum dot (QD) photoluminescence as a signal reporter. The Cu2+ doping of ZnSe QD can induce a dopant-dependent emission response, which will be inhibited after the premixing of Cu2+ with pyrophosphate (PPi), to form a Cu2+-PPi complex. Then, the hydrolysis of PPi into phosphate (Pi), specifically catalyzed by PPase, liberates the free Cu2+ to regain the QD doping for the fluorescence response, which is highly dependent on the PPase activity. The PPase can be sensitively and selectively assayed, with a detection limit of 0.1 mU/mL. The developed sensing strategy can be also employed for the PPase inhibitor screening. Thus, the current QD doping-based sensing strategy offers an efficient and promising avenue for Cu2+, PPi, or PPase-related target analysis, and might hold great potential for the further applications in the clinical disease diagnosis.

Optical and structural properties of ZnSe quantum dot with europium

Rare earth elements possessing unique 4f electrons have been investigated as excellent candidates for luminescent centers in doped II-VI nanocrystals, because of their abundant emission colors based on the 4–4f or 5d-4f transitions. In particular, ZnSe quantum dot (QDs) fabricated with the lanthanide Europium (Eu) can emit in both the visible and near-infrared region. In our work, the structural, morphological and optical properties were investigated the color-tunable ZnSe:Eu QDs. We focused on the ZnSe:Eu QDs synthesized by controlling Eu amount. According to the results, the optical property of ZnSe:Eu QDs showed that emission in the bluish to yellow-ocher range, and concentration quenching occurred upon increasing the Eu amount. The expected structure of the ZnSe:Eu QDs with Eu (Eu/Zn = 0.5, 1 and 1.5) was verified by XRD, TEM, XPS and gibbs free energy value using a HSC chemistry software.