Characterization Of CdTe Quantum Dots Research Articles

Solid and Liquid State Fluorescent Sensor Using CdTe Quantum Dots for Mercury Detection

Fluorescence based sensors are attractive owing to its ultra-sensitivity and ability to detect the analyte of interest with high specificity. Many metal ions although play vital role in ample number of biological events, few are highly toxic and even fatal.1 , 2 Hence, the field of metal ion detection using fluorescence spectroscopic technique has received tremendous attention in recent years.3 Among the fluorophores used for the metal ion detection, semiconductor based quantum dots such as CdTe, CdSe and CdS quantum dots have been exploited extensively for sensor applications on account of their bright and tuneable luminescence and ease of preparation.4 , 5 The present report focuses on the fluorescence based detection of Hg2+ ions using green-yellow emitting CdTe quantum dots, which perform as both signalling and analyte specific material. A complete characterization of CdTe quantum dots and CdTe-Hg2+ is carried out to confirm the formation of quantum dots and to understand the quenching mechanism. Here the emission of quantum dots is quenched by the addition of Hg2+, hypothesized to be due to the electron transfer mechanism. The sensor responds to Hg2+ in the linear range of 12 to 40 μM with a limit of detection 2 μM. Further, an easy visual detection strategy for Hg2+ is also established by dropcasting CdTe quantum dots over a glass plate.

Fabrication of CdTe quantum dots–apoferritin arrays for detection of dopamine

A method was proposed for detecting dopamine using a two-dimensional CdTe quantum dots (QDs)–apoferritin array fabricated on a modified silicon (Si) surface. First, CdTe QDs were synthesized in the cavity of horse spleen apoferritin (HsAFr). Then, the characterization of CdTe QDs in apoferritin was performed using photoluminescence (PL) spectroscopy. Transmission electron microscopy was used to analyze the size and structure of CdTe QDs. An atomic force microscopy image was obtained to evaluate the topography of the Si surface. In addition, the PL change resulting from the conjugation reaction of the CdTe QDs-apoferritin array with dopamine was investigated. When the array was linked to dopamine, a significant quenching of fluorescence was observed. Accordingly, the CdTe QDs–apoferritin arrays could be employed as useful sensing media for dopamine detection.

Synthesis and characterization of CdTe quantum dots by one-step method

L-Cysteine (Cys)-capped CdTe quantum dots (QDs) were prepared when sodium tellurite worked as a tellurium source and sodium borohydride acted as a reductant. The influences of various experimental variables, including pH values, Cd/Te and Cd/Cys molar ratios, on the photoluminescence (PL) quantum yield (QY) of the obtained CdTe QDs have been systematically investigated. Experimental results indicated that green to red emitting CdTe QDs with maximum quantum yield of 19.4% can be prepared at pH 11.5 and n(Cd2+):n(Te2−):n(Cys) = 1:0.07:2.0. X-Ray powder diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the crystal structure and shape of CdTe QDs. The results showed that the prepared CdTe QDs were of cubic zinc blend crystal structure in a sphere-like shape. KEY WORDS: Semicondutor nanocrystal, Chemical synthesis, Optical properties, Luminescence Bull. Chem. Soc. Ethiop. 2013, 27(3), 387-393.DOI: http://dx.doi.org/10.4314/bcse.v27i3.7

Voltammetry as a Tool for Characterization of CdTe Quantum Dots

Electrochemical detection of quantum dots (QDs) has already been used in numerous applications. However, QDs have not been well characterized using voltammetry, with respect to their characterization and quantification. Therefore, the main aim was to characterize CdTe QDs using cyclic and differential pulse voltammetry. The obtained peaks were identified and the detection limit (3 S/N) was estimated down to 100 fg/mL. Based on the convincing results, a new method for how to study stability and quantify the dots was suggested. Thus, the approach was further utilized for the testing of QDs stability.

Synthesis and Characterization of CdTe Quantum Dots Capped by N-Acetyl-L-Cysteine

The highly luminescent cadmium telluride quantum dots (CdTe QDs) have been synthesized by using N-acetyl-L-cysteine (NAC) as stabilizer in aqueous solution. Experiments indicate that the QDs nanocrystals could grow larger as the extension of reaction time, causing the red shift of emission spectra. The typical product was analyzed by fluorescence spectroscopy, high-resolution transmission electron microscope (HRTEM), x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The morphological and structural characterization confirmed the formation of monodisperse CdTe QDs with several nanometers in size.

Microstructure and optical characterization of CdTe quantum dots synthesized in a record minimum time

The CdTe quantum dots (QDs) are synthesized at room temperature in a record minimum time of 5 min by mechanical alloying the stoichiometric mixture of Cd and Te powders under Ar in a high energy planetary ball mill. Microstructure characterization of ball milled CdTe powders by x-ray diffraction employing the Rietveld structure refinement method reveals that the stoichiometric cubic CdTe phase is formed after 15 min of milling and in the course of milling upto 4 h, size of the isotropic QDs reaches ∼5 nm which is close to that obtained by transmission electron microscope (∼4.5 nm) and quite below the Bohr exciton radius of CdTe (∼6.9 nm). These QDs contain significant amount of stacking and twin faults. Microstructure characterization by high resolution TEM corroborates the findings of the x-ray analysis where the presence of stacking and twin faults on (111) plane are clearly noticed. A distinct blueshift with the decreasing particle size of the QDs in absorbance spectrum confirms the size quantization. Optical band gap of these QDs are very different from the bulk CdTe and changes with increasing milling time and that can be fine tuned with varying milling time.

Synthesis and characterization of CdTe quantum dots embedded gelatin nanoparticles via a two-step desolvation method

Novel CdTe quantum dots (QDs) embedded gelatin nanoparticles (CdTe/gelatin nanoparticles) were synthesized via a two-step desolvation method. The morphology and size distribution of the nanoparticles were characterized by transmission electron microscope (TEM) and laser particle size analyzer. They are presented spherically and relatively uniform with a diameter of 150 nm. The luminescent properties of the nanoparticles were investigated by using fluorescence spectrophotometry and fluorescence microscopy. The fluorescence stability of nanoparticles was tested in vitro. It was found that the nanoparticles were stable in water and phosphate-buffered saline (PBS) solution (pH 7.4) for at least 15 days. A possible formation mechanism of the CdTe/gelatin nanoparticles was also proposed. The inherent stability and biocompatibility indicate that the nanoparticles are expected to be promising candidates for in vivo biological imaging studies.

CdTe 양자점 합성과 물리적 특성 분석

CdTe 양자점 합성과 물리적 특성 분석

Characterization of CdTe quantum dots grown on Si(111) by hot wall epitaxy

We report on the growth and characterization of CdTe quantum dots on Si(111) by direct island nucleation. The samples were grown by hot wall epitaxy on Si(111) substrates treated with diluted HF solution only and the resulting hydrogen-terminated surface permitted the growth of good quality CdTe layers using substrate temperatures below 300 °C. The samples, grown at very low growth rates, were investigated by atomic force microscopy. Our measurements show that this system follows the Volmer-Weber growth mode, with nucleation of isolated CdTe islands on the Si substrate surface even for just 0.6 monolayers of evaporated material. As the growth proceeds, the density and size of quantum dots increase until the point at which they start to coalesce to form a uniform layer. We describe the size and density distribution of these islands as a function of growth time and substrate temperature. The results show that the Volmer-Weber growth mode can be successfully used to obtain self-assembled quantum dots of CdTe on Si, with reasonable size dispersion, using an inexpensive growth technique.