High-quality CdSe Quantum Dots Research Articles

Synthesis, Structural and Optical Investigation of Cdse Semiconductor Quantum Dots

In this paper, we present a simple synthetic route for the development of high quality CdSe quantum dots TGA capped in aqueous solutions. CdSe semiconducting Quantum dots were prepared by a chemical method at room temperature. The crystal structure, morphology, spectral and compositional properties were analyzed from X-ray Diffraction, High resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-VIS absorbance and Photoluminescence (PL), Fourier transform infrared (FTIR) and Fourier transform RAMAN (FT-RAMAN) techniques. The XRD results depicted the formation of CdSe quantum dots with an average crystallite size of 3 nm and 4 nm, which is in accordance with observations from HRTEM and TEM micrographs with an average particle diameter range between 2-3 nm. The UV-VIS absorbance peaks indicate a broad absorption behavior of CdSe quantum dots. The calculated band gap energy is found to be 2.55 eV and further it is found the particle size estimated from the maximum excitonic peaks for CdSe 2.7 nm. The photoluminescence studies evidenced that the luminesce property of quantum dots can be varied by systematically tuning precursor concentrations and the PL confirms the strong excitation peaks for the synthesized CdSe QDs with peak centered at 603 nm. The capping of TGA was confirmed from FTIR and FT-RAMAN studies. From the FTIR spectra it is observed that, for the synthesized CdSe QDs almost all the peaks are common with slightly shifting behavior towards larger and shorter wave numbers. FT-Raman analysis was performed to study the sample qualities such as micro crystallinity, homogeneity and surface conditions for the as synthesized CdSe quantum dot. The resulting colloids are very stable, and no precipitate is observed over a period of 6 months.

Microwave-assisted growth of high-quality CdSe quantum dots and its application as a sensitizer in photovoltaic cells

We introduced a fast and safe synthesis method for the growth of CdSe quantum dots (QDs). After the examination of different solvents, we chose the N-Methyl-2-pyrrolidone as an appropriate solvent and used microwave irradiation for QDs synthesis. To compare with the previous colloidal method, we also synthesized the CdSe quantum dots in the organic solvents of octadecene and liquid paraffin. Results show that the size and the bandgap energy of QDs are easily controlled in the proposed growth method. Finally, QD-sensitized solar cells show the efficiency of 3.5 %, indicating the QDs as a suitable sensitizer in a cell.

Multivariate optimization of optical properties of CdSe quantum dots obtained by a facile one-pot aqueous synthesis

Four parameters are simultaneously optimized to provide a simple, fast and reproducible synthesis procedure to obtain high-quality CdSe quantum dots.

Synthesis, Structural and Optical Investigation of CdSe semiconductor Quantum Dots

In this paper, we present a simple synthetic route for the development of high quality CdSe quantum dots TGA capped in aqueous solutions. CdSe semiconducting Quantum dots were prepared by a chemical method at room temperature. The crystal structure, morphology, spectral and compositional properties were analyzed from powder X-ray Diffraction, High resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-Vis absorbance and Photoluminescence (PL), Fourier transform infrared (FTIR) and Fourier transform RAMAN (FT-RAMAN) techniques. The XRD results depicted the formation of CdSe quantum dots with the average crystallite size of 3 nm and 4 nm, which is in accordance with observations from HRTEM and TEM micrographs predict an average particle diameter of the QDs range between 2-3 nm. The UV-Vis absorbance peaks indicate the broad absorption behavior of the synthesized CdSe quantum dots. The calculated band gap energy was 2.55 eV and further it is found the particle size estimated from the maximum excitonic peaks for CdSe 2.7 nm. The photoluminescence studies evidenced that the luminesce property of quantum dots can be varied by systematically tuning precursor concentrations. The PL emission spectrum depicts the strong excitation peaks for the synthesized CdSe QDs with peaks centered at 603 nm. The capping of TGA was confirmed from FTIR and FT-RAMAN studies. From the FTIR spectra it is observed that, for the synthesized CdSe QDs almost all the peaks are common with slightly shifting behavior towards larger and shorter wave numbers. FT-Raman analysis was performed to study the sample qualities such as microcrystallinity, homogeneity and surface conditions for the as synthesized CdSe quantum dot. The resulting colloids are very stable, and no precipitate is observed over a period of 6 months.

A facile method to synthesis high-quality CdSe quantum dots for large and tunable nonlinear absorption

The CdSe nanocrystals (NCs) were synthesized by a hot injection method in the atmospheric environment without any protective gas. The size of CdSe NC was tuned by controlling the growth time and the NCs' high-quality was confirmed by UV–visible spectroscopy, photoluminescence spectroscopy, X-ray diffraction and transmission electron microscopy. A large third-order nonlinear optical (NLO) absorption of CdSe NCs was obtained by using Z-scan technique with 30 ps excitation at 532 nm, which was tunable with variable size and the energy difference between the first exciton absorption peak and the laser wavelength. The NLO susceptibility of CdSe NCs can reach as high as 1.81 × 10−10 esu at the size of 3.3 nm and at resonance absorption peak.

Facile synthesis of CdSe quantum dots in a high-boiling two-phase liquid/liquid system

We introduce a facile way to synthesize high-quality CdSe quantum dots (QDs) in a high-boiling two-phase liquid/liquid system. The cadmium myristic acid salt (Cd-MA) dispersed in the dimethylbenzene and selenourea dissolved in the ethylene glycol (EG) reacted at the two-phase interface for the nucleation and growth of nanocrystals. The n-trioctylphosphine oxide (TOPO) was used as capping agent of the CdSe QDs. In this route, the selenourea used as the precursor was dissolved in viscous ethylene glycol (EG), which facilitated the control of the nanocrystal growth by virtue of the slow decomposition and diffusion of selenourea in EG. The size, shape, crystalline structure and optical properties of CdSe QDs were investigated by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV⿿vis spectrometer and photoluminescence spectroscopy. This route could be exploited to synthesize nanocrystals with a large scale and could broaden to synthesis of metal or other semiconductor nanocrystals.

Intensification of nucleation stage for synthesizing high quality CdSe quantum dots by using preheated precursors in microfluidic devices

We developed a simple and facile microfluidic approach to continuously synthesize high quality CdSe quantum dots by using preheated precursors. The preheating process could intensify the burst of nucleation, and CdSe quantum dots with smaller size would be synthesized compared to previous methods using room-temperature precursors directly. Besides, a burst of nucleation stage and a stable growth stage without prolonged nucleation could reduce the size distribution of CdSe quantum dots through the preheating process. By this method, high quality quantum dots with small size or high quality crystal seeds could be synthesized easily, which is necessary for the synthesis of small core–shell quantum dots or large quantum dots with high monodispersity.

Green Synthesis of High Quality CdSe Quantum Dots: High Luminescence in Green to Red Region

Green Synthesis of High Quality CdSe Quantum Dots: High Luminescence in Green to Red Region

Continuous synthesis of high quality CdSe quantum dots in supercritical fluids

Demonstration of a powerful scalable continuous supercritical fluids approach to synthesize high quality CdSe quantum dots (QDs).

Surface passivation of CdSe-TOPO quantum dots by poly(acrylic acid): solvent sensitivity and photo-induced emission in water

The principal available methods for the preparation of high quality CdSe quantum dots (QDs) are based on organic ligands such as tri-n-octylphosphine oxide (TOPO) which lead to non-water soluble nanocrystal QDs. As most biological interactions take place in aqueous media, much effort has been made on preparation of water soluble QDs. In this report, the water soluble CdSe QDs were prepared via a ligand exchange process between organic soluble CdSe-TOPO quantum dots and poly(acrylic acid). The poly(acrylic acid) (PAA) can attach onto the surface of CdSe-TOPO quantum dots in a ligand exchange process to make water-soluble CdSe-PAA complexes. In spite of CdSe-TOPO QDs, the resultant CdSe-PAA QDs are soluble in polar solvents such as methanol or water. Optical properties of CdSe-PAA QDs in several solvents showed that the emission intensity of QDs was mainly decreased in protic solvents such as methanol or water. The TEM images of dots in different solvents were examined and some aggregation of dots was found in protic solvents. In comparison with PAA, the addition of PDMAEMA to the solution of CdSe-TOPO QDs in THF increased the emission intensity of QDs. Furthermore, we found that the entitled ligand exchange process was fast and conjugation process completed at short time intervals. The UV-irradiation of the CdSe-PAA conjugate in water showed that the emission was amplified by increasing the irradiation time.

Synthesis of high-quality CdSe quantum dots in aqueous solution

By employing sodium selenite as selenium source and mercaptosuccinic acid (MSA) as stabiliser, the authors demonstrate that high-quality CdSe quantum dots (QDs) can be conveniently prepared in aqueous solution. The obtained products were characterised by UV–vis absorption, photoluminescence spectra, X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). XRD analysis showed that the MSA-capped CdSe QDs were of cubic zinc-blende crystal structure, UV–vis absorption spectra and TEM exhibited that the QDs were nearly monodisperse and relatively uniform. The quantum yield of as-prepared CdSe QDs can reach up to 18%, and the full-width at half-maximum value was merely 35 nm.

49.3: Synthesis of High Quality CdSe Quantum Dots with Tunable Size

AbstractA cheaper, greener approach for the synthesis of highly monodisperse and tunable size CdSe semiconductor quantum dots was developed by thermolysis of a mixed solution of CdO and Se in non‐coordinating solvent 1‐octadecene at 240°C. Systematic vary of the precursor molar ratios allowed the particle size (from 2.5 nm to 5.5 nm) to be tuned and the size distribution (full width at half maximum of photoluminescence spectra from 26 nm to 37 nm) to be controlled. The results revealed that initial Cd:Se molar ratios play an important role in controlling both the size and size distribution of the as‐prepared CdSe quantum dots. Moreover, the obtained CdSe quantum dots are all of zinc blende phase. The possible reason was discussed. The reaction has been conducted in relatively low temperature at 210°C in the absence of expensive organic phosphine ligands, such as trioctylphoshine and trioctylphoshine oxide. This approach has great value for both the laboratory research and industrial application in term of “green chemical principles”.

Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage (∼2.2V) .The EL peak intensity was found to increase by increasing the operating current.

CdSe Quantum Dots Decorated by 3-Aminobenzeneboronic Acid as Fluorescence Probe for Glucose

A simple route to the production of high-quality CdSe quantum dots (QDs) is presented. The characterization of CdSe QDs was measured by Zetasizer Nano ZS, ultraviolet-visible spectoscopy and fluorospectrophotometer. The CdSe QDs were decorated by 3-Aminobenzeneboronic acid to obtain good fluorescent characteristic. Under the optimal conditions, the decreased normalized absorbance was linear to the concentration of glucose from 1.0×10−7 to 2.9×10−6 mol·L-1with a detection limit of 5.0´10-8mol·L-1. The relative standard deviation (RSD) for the determination of 1.0×10-7mol·L-1was 1.4 % by 11 replicate determination. In this paper, the fluorescent behavior of glucose with the decorated CdSe QDs was studied, and it is found that the system has a high sensitivity and selectivity for analysis of glucose.

ChemInform Abstract: Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production.

AbstractHigh‐quality CdSe quantum dots are synthesized by microwave heating of aqueous solutions containing Cd(OAc)2, Na2SeSO3, NaOH, EtOH, and oleic acid (40—120 °C, 1—15 min, 80—140 W).

Optimized Synthesis of Water-Soluble and Small-Size CdSe Quantum Dots

An optimized synthesis route was applied for controlling the preparation of CdSe quantum dots (QDs) in an aqueous solution. Some key factors which influencing the properties of CdSe QDs, such as initial pH, ratio of precursor etc, were investigated. The as-prepared products have been characterized by TEM, XPS, XRD, UV-Vis and fluorescence (FL) spectra. The result showed that the high-quality CdSe QDs with 3 nm was obtained. The experiments also conformed that the CdSe QDs with better FL properties were obtained with properly initial pH, 5, suitably [Cd2+] / [SeSO3 2-], range from 1:0.25 to 1:0.75 and the ratio of [Cd2+] / [TGA] is 1:2~1:3.

Controlled Synthesis of CdSe Quantum Dots by a Microwave‐Enhanced Process: A Green Approach for Mass Production

A method that does not employ hot-injection techniques has been developed for the size-tunable synthesis of high-quality CdSe quantum dots (QDs) with zinc blende structure. In this environmentally benign synthetic route, which uses less toxic precursors, solvents, and capping ligands, CdSe QDs that absorb visible light are obtained. The size of the as-prepared CdSe QDs and thus their optical properties can be manipulated by changing the microwave reaction conditions. The QDs were characterized by XRD, TEM, UV/Vis, FTIR, time-resolved fluorescence spectroscopy, and fluorescence spectrophotometry. In this approach, the reaction is conducted in open air and at a much lower temperature than in hot-injection techniques. The use of microwaves in this process allows for a highly reproducible and effective synthesis protocol that is fully adaptable for mass production and can be easily employed to synthesize a variety of semiconductor QDs with the desired properties. Possible applications of the CdSe QDs were assessed by deposition on TiO(2) films.

Synthesis and photoluminescence properties of high-quality CdSe quantum dot in liquid paraffin

High-quality cadmium selenide (CdSe) quantum dots (QDs) were synthesised in liquid paraffin with a mixture of octadecylamine and trioctylphosphine oxide as stabilising ligands. The synthesised CdSe QDs were characterised by ultraviolet–visible absorption and photoluminescence spectroscopy, transmission electron microscopy and selected area electron diffraction techniques. Compared with CdSe QDs synthesised in liquid paraffin stabilising with only oleic acid, CdSe QDs synthesised by this new route possess higher quantum yields, more symmetric and narrower emission spectra. The new route enables us to achieve high-quality CdSe QDs in less expensive solvent, liquid paraffin.

Ambient Synthesis and Characterization of High-Quality CdSe Quantum Dots by an Aqueous Route

Herein, we report the ambient synthesis of CdSe nanoparticles of widely tunable particle size by a solution route. The proposed protocol uses hydrazine hydrate to form an air-stable complex of selenium. These nanoparticles are characterized by X-ray diffraction, FTIR, optical absorption, photoluminescence, and transmission electron microcopy measurements. By varying the molarities of Cd(2+) and Se(2-) ions in solution with 3-mercaptopropionic acid as the capping ligand, the method permits us to synthesize nanoparticles of size ranging from 1.58 to 3.42 nm (estimated from optical absorption edge measurements) by controlling the annealing time of the starting colloid at 100 degrees C. The extracted quantum dots are of high quality (40% photoluminescence quantum yield) and exhibit colors ranging from deep blue to red. The resulting colloids are very stable, and no precipitate is observed over a period of 6 months. Thus, the method is simple and easily scalable to synthesize fluorescent CdSe nanoparticles.

Phosphine-Free Synthesis of CdSe Quantum Dots in a New Co-CappingLigand System

High-quality CdSe quantum dots with zinc blende structure were successfully synthesized via a new cheaper, greener phosphine-free route, using environmentally friendly N,N-dimethyl-oleoyl amide as the solvent of Se. The process eliminates trioctylphoshine from the synthesis, using oleic acid (OA) as a primary capping ligand and benzophenone (BP) as a secondary ligand in the noncoordinating solvent. It has been found that the addition of BP can improve the size distribution (below 10%) of as-synthesized CdSe quantum dots greatly, and the nucleation and growth process can also be well-separated. Moreover, a comprehensive examination on the control of particle size and size distribution was performed by systematically varying the BP/OA molar ratio. The phosphine-free route enables us to obtain high-quality CdSe quantum dots with sharp UV-vis absorption peak, size ranging from 2.8 to 6.8 nm, and narrow full width of half-maximum between 27 and 35 nm with purely band-edge luminescence, and without any post-synthesis processing.