Growth and optical characterization of colloidal CdTe nanoparticles capped by a bifunctional molecule (original) (raw)
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Optical properties of thiol-stabilised CdTe nanoparticles
… Journal of Nanoparticles, 2009
Thiol-capped CdTe nanocrystals with cubic zinc blende structure were synthesised in aqueous solution by wet chemical route and microwave assisted method. A series of cadmium telluride (CdTe) nanoparticles capped with mercaptoacetic acid were prepared using different pH values. The synthesised nanoparticles have been characterised with Raman, FT-IR, ultraviolet visible (UV-Vis) absorption, fluorescence spectroscopy and X-ray powder diffraction (XRD) studies.
The role of potassium tellurite as tellurium source in mercaptoacetic acid-capped CdTe nanoparticles
Current Applied Physics, 2010
Water-soluble CdTe nanoparticles were synthesized in aqueous solution with the assistance of mercaptoacetic acid (MAA) molecules by wet chemical route and microwave-assisted method. A series of cadmium telluride (CdTe) nanoparticles capped with a bifunctional molecule, which contains both thiols and carboxylic acid groups were prepared using different pH values and using potassium tellurite as tellurium source. Thiol-capped nanocrystals of CdTe can be isolated as powders using 2-propanol. The synthesized thiol-capped CdTe were characterized with EDAX, TEM, Raman, FT-IR, UV-Visible absorption, fluorescence spectroscopy and X-ray diffraction (XRD) for the particle size determination and to understand their optical properties. The particles crystallize predominantly in cubic phase with narrow photoluminescence emission. Potassium tellurite as source of tellurium improves the photoluminescence efficiency and also avoids the cumbersome processes associated with H 2 Te or NaHTe sources.
Effect of chemical composition on luminescence of thiol-stabilized CdTe nanocrystals
Nanoscale Research Letters, 2007
Judicious selection of the amount of surfactant during synthesis enables a drastic increase in the photoluminescence efficiency of aqueous CdTe nanocrystals (NCs) stabilized by thioglycolic acid (TGA). Elemental determination of the NCs was undertaken to identify the origin of this effect. The molar ratio of (Te + S) to Cd approached unity when the optimum amount of TGA was used during synthesis, whereas the number of S atoms originating from TGA molecules in one NC (2.6 nm of diameter) remained unchanged at 90 ± 3. This indicates that the core lattice composition at the beginning of synthesis, rather than the surface conditions, affects the photoluminescence efficiency of the NCs even after prolonged refluxing.
Synthesis and characterization of thiol-stabilized CdTe nanocrystals
Berichte der Bunsengesellschaft für physikalische Chemie, 1996
In order to expand the range of high-quality nanosized semiconductor materials that can be obtained as quantum dots through a wet chemical route a series of oxidize-stable CdTe nanoclusters with narrow size distributions and extremely small particle sizes ranging from 1.3 to 2.4nm has been prepared in aqueous solution using 2-mercaptoethanol and 1 -thioglycerol as stabilizers. It has been investigated by means of UV-vis absorption and photoluminescence spectroscopy, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive x-ray analysis (EDX).
Physical Chemistry Chemical Physics, 2016
The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which-together with alloyed Cd x Hg 1Àx Te-are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D 2 O and compared to the results from previous dilution studies with a set of thiol-capped Cd 1Àx Hg x Te SC NCs in D 2 O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman's test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H 2 O compared to D 2 O, underlining also the role of hydrogen bonding and solvent molecules.
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.
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.
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.
Nanotechnology, 2008
The influence of thioalkyl acid ligand was evaluated during aqueous synthesis at 100 • C and under hydrothermal conditions (150 • C) of CdTe and CdSe quantum dots (QDs). Experiments performed with 3-mercaptopropionic acid (MPA), 6-mercaptohexanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) demonstrated that the use of MHA and MUA allowed for the preparation of very small nanoparticles (0.6-2.5 nm) in carrying out the reaction under atmospheric pressure or in an autoclave and that the photophysical properties of QDs were dependent on the ligand and on the synthesis conditions. The influence of various experimental conditions, including the Te-to-Cd ratio, temperature, and precursor concentration, on the growth rate of CdTe or CdSe QDs has been systematically investigated. The fluorescence intensities of CdTe QDs capped with MPA, MHA, or MUA versus pH were also found to be related to the surface coverage of the nanoparticles.