As-prepared CdSe Quantum Dots Research Articles

One-Step Synthesis of CdSe Quantum Dots by Using Hydrazine Hydrate Reduction of Selenium Dioxide

Hydrazine hydrate was used as a novel reducing agent for the synthesis of water soluble and stable cadmium selenide (CdSe) quantum dots (QDs). The as-prepared CdSe quantum dots were investigated by X-ray powder diffraction, high-resolution transmission electron microscopy, photoluminescence, and UV-vis absorption spectroscopy analyses. The results show that the as-prepared CdSe QDs possess a cubic crystal structure and an average size of 2 nm. The effects of the pH of the original solution, thioglycollic acid (TGA)/Cd2+ molar ratio (nTGA/nCd2+), and the Cd/Se molar ratio on the luminescence properties of CdSe QDs were also systematically analysed.

Composition-controlled optical properties of colloidal CdSe quantum dots

A strategy with respect to band gap engineering by controlling the composition of CdSe quantum dots (QDs) is reported. After the CdSe QDs are prepared, their compositions can be effectively manipulated from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich QDs. To obtain Cd-rich CdSe QDs, Cd was deposited on equimolar CdSe QDs. Further deposition of Se on Cd-rich CdSe QDs produced Se-rich CdSe QDs. The compositions (Cd:Se) of the as-prepared CdSe quantum dots were acquired by Energy-dispersive X-ray spectroscopy (EDX). By changing the composition, the overall optical properties of the CdSe QDs can be manipulated. It was found that as the composition of the QDs changes from 1:1 (Cd:Se) CdSe to Cd-rich and then Se-rich CdSe, the band gap decreases along with a red shift of UV–vis absorption edges and photoluminescence (PL) peaks. The quantum yield also decreases with surface composition from 1:1 (Cd:Se) CdSe QDs to Cd-rich and then to Se-rich, largely due to the changes in the surface state. Because of the involvement of the surface defect or trapping state, the carrier life time increased from the 1:1 (Cd:Se) CdSe QDs to the Cd-rich to the Se-rich CdSe QDs. We have shown that the optical properties of CdSe QDs can be controlled by manipulating the composition of the surface atoms. This strategy can potentially be extended to other semiconductor nanocrystals to modify their properties.

Synthesis of Color-Tunable CdSe Nanocrystals via a Green Synthetic Method

In this letter, ascorbic acid was used as a novel and environmental friendly reducing agent in the synthesis of high-quality L-cysteine-capped CdSe nanocrystals. The X-ray diffraction and high-resolution transmission electron microscope results show that the as-prepared CdSe quantum dots (QDs) had a cubic crystal structure with an average size of 5 nm. The synthetic conditions were optimized by adjusting the n(L-Cys)/n(Cd2+), pH, and Cd/Se molar ratios. Under optimum conditions, the quantum yield of CdSe QDs reached 22%.

Self-Replication Fabrication of Ligand-Free CdSe Quantum Dots on a Nanofiber Microreactor via a Solid–Liquid Interfacial Method

In this work, we present the self-replication fabrication of oil-soluble and ligand-free CdSe quantum dots (QDs) via a “solid–liquid interface” method using electrospun nanofibrous mats as the microreactor. The electrospun sodium alginate-based nanofibers with the cadmium source act as the solid phase, while octadecene containing selenium in trioctylphosphine as the Se source serves as the liquid phase. After reacting on the nanofibrous microreactor, the as-prepared CdSe QDs without using any ligands are released from the microreactor, presenting a monodispersion with a mean diameter of ∼3 nm along with good fluorescent properties (λem = 620 nm). ZnSe QDs could also be prepared in the same manner, indicating this self-replication method to have wide suitability for the construction of QDs via this solid–liquid interface microreactor. For practice, we further applied the CdSe QDs as fluorescent inks for versatile printing of luminescent patterns toward anticounterfeit and optoelectronic applications.

One-step microwave-assisted synthesis of water soluble CdSe quantum dots for white light-emitting diodes with excellent color rendering

Thiol-capped and red-emitting CdSe quantum dots (QDs) have been successfully synthesized in the air without hot-injection by one-step microwave method with friendly environment. The size and optical properties can be tuned by changing the reaction time, growth temperature, microwave power, and the Cd2+/Se molar ratio. The as-prepared CdSe QDs were mixed with the yellow-emitting YAG:Ce phosphor and coated onto a blue LED chip, a white LED with an excellent color rendering property was obtained. It exhibited a luminous efficiency of 67lm/W and a Ra as high as 85, which is acceptable for general lighting. It indicates that the combination of the phosphor and QD in LEDs should be a good solution to obtain white light sources with high color rendering.

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.

Aqueous synthesis of highly monodispersed thiol-capped CdSe quantum dots based on the electrochemical method

A facile green approach is developed to control the growth regime in the aqueous synthesis of CdSe semiconductor quantum dots (QDs) based on the electrochemistry method. The low growth temperature and slow injection of Se precursors are used to prolong the diffusion controlled stage and thus suppress the Ostwald ripening during nanocrystal growth. The experimental results show that a low concentration of Se precursor would definitely influence the growth procedure. The narrow absorption peaks in the UV–visible absorption spectra, as well as transmission electron microscopy images indicate that the as-prepared CdSe QDs have a good monodispersity. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggest that the as-prepared QDs have high crystallinity and cubic structure. The QDs exhibit high fluorescence QYs of about 30% without any postpreparative treatment over a broad spectral range of 560–660nm, which could be further broadened by long-term refluxing. The current work suggests that the electrochemical method is an attractive approach to the synthesis of high-quality II–VI semiconductor QDs at a large scale.

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”.

Studies on light emitting CdSe quantum dots in commercial polymethylmethacrylate

CdSe quantum dots (QDs) prepared using an aqueous sodium selenosulphite and N, N′-dimethylformamide (DMF) in commercial polymethylmethacrylate (PMMA) showed excellent optical properties. Tuning of the absorption and emission wavelengths by varying the selenium concentration with respect to cadmium is studied. As-prepared CdSe quantum dots showed absorption band at 405 nm (3.06 eV) associated with the formation of ‘early-stage’ CdSe nano-particles along with weak absorption at 480–90 nm due to continuous growth of the particles. The blue-green and yellow-green light emissions were observed from as-prepared solutions. Photoluminescence (PL) measurement showed band-edge emissions at around 430 nm for small clusters but a more stable emission at 544 nm for the 1:1 CdSe sample. X-ray diffraction (XRD) pattern of the CdSe/PMMA powder with Cd/Se ratio of 1:1 showed broad pattern for cubic CdSe. Transmission electron microscopy (TEM) showed cube like de-shaped spherical dots in the region of about 5 nm.

Photoacoustic characterization of optical and thermal properties of CdSe quantum dots

We report on the optical absorption properties of as prepared CdSe quantum dots (QDs) measured by the photoacoustic (PA) method. CdSe QDs were fabricated by the chemical solution deposition (CD) technique. With increasing growing time, the redshift of the PA spectra can be clearly observed and optical absorption in the visible region due to CdSe Q-dots is demonstrated. The average diameters of the CdSe QDs for each growth time interval is estimated using the effective mass approximation giving diameters ranging from 2.6 nm to 3.4 nm. These values are comparable to those obtained by scanning tunnelling microscope (STM). Thus, PA spectroscopy is useful to obtain the QDs sizes as grown and with no further preparation. In addition, PA measurements provide also the thermal diffusivity of samples of different sizes which in this case show an increase by at least an order of magnitude than the bulk value.

Phosphine-free Fabrication of CdSe Quantum Dots with Good Thermal Stability and Promising Application in Multiplexed Bioassay

Abstract High-quality cadmium selenide (CdSe) quantum dots (QDs) with good thermal stability were prepared by using liquid paraffin as a solvent and oleic acid as a ligand under relative low temperatures. Moreover, the as-prepared CdSe quantum dots were embedded into the porous polystyrene (PS) beads to fabricate optically encoded beads, which suggests their promising application in multiplexed bioassays.

Synthesis and characterization of mondispersed CdSe nanocrystals at lower temperature

Nearly monodispersed CdSe quantum dots have been prepared by a soft solution approach using air-stable reagents at lower temperature. The temporal evolution of the absorption and room temperature photoluminescence spectra were used to follow the reaction process and to characterize the optical properties of as-prepared CdSe quantum dots. The results exhibited clear exciton peaks in absorption and bright band-edge luminescence. The structures of the CdSe nanocrystals were determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The influence of the temperature on the properties of the resultant CdSe nanocrystals was investigated. The distribution of properties within ensembles of CdSe nanocrystals was also studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed.