A Novel Organometallic Synthesis of Highly Luminescent CdTe Nanocrystals (original) (raw)
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Journal of Applied Spectroscopy, 2012
A colloidal suspension method is used to obtain CdTe nanocrystals modified with thioglycolic acid in aqueous solutions of ethylene glycol. Their photoluminescence spectrum is shifted to shorter wavelengths relative to that of CdTe nanocrystals synthesized in water. It is found that the ethylene glycol molecules participate in the stabilization of the nanocrystals and passivation of surface defects, with an optimum concentration of 10% ethylene glycol in the reactive mixture for production of stably dispersed CdTe. It is difficult to observe plasmon effects in these nanoparticles when Ag nanoparticles are present because cadmium iodide is used as a precursor salt, which leads to the appearance of I 2 , an oxidant for Ag nanoparticles, in the solution. When a protective polyelectrolyte intermediate layer of thickness ~11.7 nm is deposited on a colloidal silver substrate, the photoluminescence intensity of the CdTe nanoparticles increases by a factor of 1.7. The chemical features of these nanoparticle solutions cause their luminescence characteristics to be highly sensitive to the presence of Ag nanoparticles in the solution. Changes in the position and intensity of the photoluminescence peak are observed for concentrations of Ag nanoparticles in the solution as low as 10 -11 mol/l.
Synthesis and characterization of brightly photoluminescent CdTe nanocrystals
Surface Science, 2007
A new synthesis procedure for the preparation of spherical shaped CdTe nanocrystals (NCs) is presented, exhibiting bright luminescence with exceptionally high quantum efficiency (up to 85%). The growth of these NCs occurs in a non-coordinating solvent, octadecene, with the addition of oleic acid/tri-octylphosphine stabilizers, CdO as a precursor for the Cd monomers and additional Cd metal particles as a supplementary Cd reservoir source. The dependence of the crystalline quality and the optical properties of the CdTe NCs, on the initial Cd:Te precursors' molar ratio, and the reaction duration were investigated. It was demonstrated that the NCs' properties improved significantly as the initial Cd:Te molar ratios are increased. The obtained NCs' properties were correlated with measurements of the Cd 0 concentration in Cd metal particles, CdTe NCs and in Cd monomer solutions.
Luminescence of CdTe nanocrystals
Journal of Luminescence, 2003
The growth of highly luminescent CdTe nanocrystals synthesized in a mixture of tri-octylphosphine and dodecylamine was investigated. The CdTe nanocrystals grow in time to a constant size which is dependent on the reaction temperature. In the initial stage of the growth particles show a broad defect emission band which is replaced by an efficient excitonic emission after a few minutes of growth. Quantum yields up to 45% were obtained. The life time of the exciton emission increases with quantum yield and reaches a constant value of about 10 ns for the most efficient particles. The life time increase is explained by the reduction of the (fast) non-radiative decay for samples with a higher quantum yield. In CdTe samples aged at room temperature sharp absorption peaks at discrete energies were observed.
ChemistrySelect, 2019
The nature of the capping ligands used and the strength of their interactions with the surface atoms of the nanoparticles (NPs) impact greatly on the material properties and the stability of the resulting NPs. The structural analysis revealed that all the as-prepared CdTe NPs samples had a zinc blende crystal structure of different phases. The glutathione and L-cysteine capped CdTe NPs had the same zinc blende phase (JCPDS no. 75-2086) while thioglycolic acid capped and co-capped CdTe NPs possessed another zinc blende phase (JCPDS no. 75-2083). The calculated crystallite sizes were in the range 2-26 nm for all the samples. The optical spectroscopy studies showed various properties when different capping ligands were used. The band gap energies for all the as-prepared CdTe NPs confirmed the results obtained from the X-ray diffraction. The band gap energies were in the range of 2.39-3.34 eV for all the as-prepared CdTe NPs.
The physico-chemical properties of low-dimensional structures based on CdTe obtained in the course of colloidal synthesis have been investigated. Analyzed have been the main photoluminescence characteristics of CdTe nanocrystals, which are stabilized by thioglycolic acid and obtained using the deionized water and aqueous solutions of ethylene glycol and glycerol with different concentrations as dispersion environment. It has been shown that stability of colloidal solutions of CdTe nanocrystals depends on the nature of dispersion environment and concentration of stabilizer.
Synthesis of CdTe Quantum Dots in Aqueous Solution and Their Optical and Structural Characterization
Science of Advanced Materials, 2012
We describe the optical and structural characterization of highly luminescent thioglycolic acid-stabilized CdTe quantum dots (CdTe-QD) synthesized in water. Samples prepared under different reflux times were characterized using transmission electron microscopy (TEM), X-ray diffraction, Raman spectroscopy, absorbance and photoluminescence techniques. TEM measurements revealed CdTe-QD having a nearly spherical shape (2.5 nm in size), so as tellurium nanorods in the same sample. The corresponding Raman spectrum displays a characteristic peaks of CdTe (broad bands at 141 cm −1 and 162 cm −1 , respectively) and tellurium nanorods (121 cm −1). Three extra peaks at 228, 252 and 277 cm −1 could be associated to the TO 1 and LO 2 modes of CdS nanoparticles. X-ray diffraction measurements done on dried sample indicated the face-centered cubic structure for CdTe and testified the presence of CdS nanoparticles, crystallizing in the hexagonal phase. All refluxed samples exhibit high luminescence that increases with reflux time. Their absorbance spectra display a well resolved excitonic peak in the 350-510 nm range, whilst photoluminescence peaks shift red (500-600 nm) due to the Stokes shift. To explain the observed strong luminescence, it is assumed that a CdS shell develops at the CdTe surface due to the thioglycolic acid decomposition, providing the surface passivation.
Synthesis and characterization of colloidal CdTe nanocrystals
Nanoengineering: Fabrication, Properties, Optics, and Devices V, 2008
We synthesized CdTe nano crystals (NCs) in uniform sizes and in good quality as characterized by photoluminescence (PL), AFM, and X-ray diffraction. In this growth procedure, CdTe nano-crystal band gap is strongly dependent on the growth time and not on the injection temperature or organic ligand concentration. This is very attractive because of nano-crystal size can be easily controlled by the growth time only and is very attractive for large scale synthesis. The color of the solution changes from greenish yellow to light orange then to deep orange and finally grayish black to black over a period of one hour. This is a clear indication of the gradual growth of different size (and different band gap) of CdTe nano-crystals as a function of the growth time. In other words, the size of the nano-crystal and its band gap can be controlled by adjusting the growth time after injection of the tellurium. The prepared CdTe NCs were characterized by absorption spectra, photoluminescence (PL), AFM and X-ray diffraction. Measured absorption maxima are at 521, 560, 600 and 603 nm corresponding to band gaps of 2.38, 2.21,2,07 and 2.04 eV respectively for growth times of 15, 30, 45 and 60 minutes. From the absorption data nano-crystal growth size saturates out after 45 minutes. AFM scanning of these materials indicate that the size of these particles is between 4 -10 nm in diameter for growth time of 45 minutes. XD-ray diffraction indicates that these nano crystals are of cubic zinc blende phase. This paper will present growth and characterization data on CdTe nano crystals for various growth times.
Luminescence studies of heat treatment influence on size distribution of CdTe nanocrystals
physica status solidi (c), 2006
Variations in absorption and emission spectra induced by thermal treatment are reported for aqueous solutions of thiol-stabilized CdTe nanocrystals with different Cd 2+ :Te 2molar ratios. Heating of colloids was shown to result in appearance of two photoluminescence lines that were assigned to two ensembles of nanocrystals with different mean diameters. Effect of heat treatment on size distribution, absorption and emission properties, and stability of nanocrystals with various Cd 2+ :Te 2molar ratios is discussed in the terms of different coverage of the nanocrystal surfaces with tellurium atoms (ions?) and with thioglycolic acid molecules.
Synthesis and optical properties of CdTe nanocrystals with improved optical properties
Indian Journal of Engineering and Materials Sciences, 2009
CdTe nanocrystals are prepared by hydrothermal route using the reaction between Cd 2+ and KHTc in the presence of thioglycolic acid as the stabilizing agent. Hydrothermal synthesis under optimum conditions resulted in a rapid growth. CdTe nanocrystals with high PL intensity and narrow PL spectra are obtained in less time. The growth mechanism of CdTe nanocrystals is investigated. The growth rate in the initial stage of synthesis is higher in hydrothermal synthesis resulting in an increased growth in diffusion controlled focused region.