CdTe Semiconductor Nanocrystals Research Articles

Synthesis of Group II-VI Semiconductor Nanocrystals via Phosphine Free Method and Their Application in Solution Processed Photovoltaic Devices.

Solution-processed CdTe semiconductor nanocrystals (NCs) have exhibited astonishing potential in fabricating low-cost, low materials consumption and highly efficient photovoltaic devices. However, most of the conventional CdTe NCs reported are synthesized through high temperature microemulsion method with high toxic trioctylphosphine tellurite (TOP-Te) or tributylphosphine tellurite (TBP-Te) as tellurium precursor. These hazardous substances used in the fabrication process of CdTe NCs are drawing them back from further application. Herein, we report a phosphine-free method for synthesizing group II-VI semiconductor NCs with alkyl amine and alkyl acid as ligands. Based on various characterizations like UV-vis absorption (UV), transmission electron microscope (TEM), and X-ray diffraction (XRD), among others, the properties of the as-synthesized CdS, CdSe, and CdTe NCs are determined. High-quality semiconductor NCs with easily controlled size and morphology could be fabricated through this phosphine-free method. To further investigate its potential to industrial application, NCs solar cells with device configuration of ITO/ZnO/CdSe/CdTe/Au and ITO/ZnO/CdS/CdTe/Au are fabricated based on NCs synthesized by this method. By optimizing the device fabrication conditions, the champion device exhibited power conversion efficiency (PCE) of 2.28%. This research paves the way for industrial production of low-cost and environmentally friendly NCs photovoltaic devices.

Synthesis of CdTe Semiconductor Nanocrystals on Hydrotalcite Matrix Surface for Electrochemical Detection of Ciprofloxacin

The synthesis of CdTe in the inorganic hydrotalcite matrix (LDH) was performed to form a hybrid material with synergistic properties to develop a sensitive and selective electrochemical method for the detection of ciprofloxacin (CPX). Despite its pharmacological relevance, CPX can be considered an emerging pollutant with known environmental effects [1-2], being found in μg L-1 to ng L-1 concentration ranges in both hospital and domestic effluents. For this reason, several analytical methods have been proposed for the determination of CPX [3-4]. Compared with other instrumental methods, electrochemistry fulfils such requirements with the possibility of electrode modification in order to become increasingly sensitive and selective to antibiotics [5-6]. Thus, the development of increasingly sensitive, novel low cost and simple electrochemical methods for CPX determination is highly desirable. The emission and absorption spectroscopies highlighted the growth of the CdTe semiconductor nanocrystals in the inorganic matrix [7]. Cyclic voltammetry confirmed the presence of CdTe grown in LDH (Figure 1a). The A1 oxidation peak (+0.35V) can be assigned to surface defects related to dangling bonds, while the other two peaks, A2 (+1.20V) and C1 (-1.32V) are assigned respectively to oxidation of the tellurium species in CdTe nanocrystals and the cathodic potential of refers to the reduction of oxidation products of metallic nature (CdTe + 6OH- → Cd2+ + TeO3 2- + 3H2O + 6e-). Carbon paste electrodes (CPE) and modified electrodes (MCPE) immobilizing LDH and synthesized hybrid (LDH/QD) were prepared for CPX detection (Figure 1b). The modified electrode obtained by the immobilization of LDH/QD presented better sensitivity for the detection of ciprofloxacin. The use of 20% in the paste composition at BR buffer (pH 6.0) during 300 s accumulation time and 20 mV s-1 scanning speed favored the analytical signal in terms of intensity and resolution. The analytical curve (Figure 1c) was determined from differential pulse voltammetry evidencing a linear behavior (R2 = 0.995) for CPX concentrations in the 2.5 x 10-8 – 1.2 x 10-5 mol L-1 range. The resulting equation was Ip,a(μA) = 3.00[CPX] – 7.00 x 10-5 where Ip,a refers to the anodic peak current, while [CPX] is concentration of ciprofloxacin. The limit of detection (LOD) was found to be 4.2 x 10-8 mol L-1 (three point three times the signal blank/slope) and limit of quantification (LOQ) was1.3 x 10-7 mol L-1 (ten times the signal blank/slope). In order to get information about the selectivity of MCPE/LDH-QD for CPX, an interference study was carried out in the presence of potential interferers (Zn2+, Fe2+, Cu2+, citric acid and ascorbic acid) using 0.1:1; 1:1; 10:1 interferer:CPX ratios. The CPX signal decreased in the presence of Zn2+, Fe2+ and Cu2+, with negligible effects for the low interferer concentrations. On the other hand, both citric and ascorbic acids interfered positively in CPX determination, since the current intensity increased slightly. A relative standard deviation (RSD) of 3.0% was found for CPX determination, indicating a remarkable reproducibility and precision, with 94% of recovery. The modified electrode was stored for two months at 4 °C, keeping the response at 95% of its initial value, suggesting that the MCPE-LDH/QD electrode is significantly stable. The method developed here was also applied to determine CPX in commercial 500 mg tablets. A certain weight of the tablet, milled and homogenized, was dissolved in 10 mL of ultrapure miliQ water. Ciprofloxacin was determined by the standard addition method and the result obtained (495 mg) is in agreement to the declared CPX content. Acknowledgements: FAPITEC, CNPq, CAPES, Corrosion and Nanotechnology Laboratory – NUPEG and CLQM (Center of Chemistry Laboratories Multi-users) from Federal University of Sergipe for the analysis support. [1] Shan, J.; Liu, Y.; Li, R.; Wu, C.; Zhu, L.; Zhang, J.; J. Electroanal. Chem. 2015, 738, 123. [2] Zhang, Y.; Cai, X.; Lang, X.; Qiao, X.; Li, X.; Chen, J.; Environ. Pollut. 2012, 166, 48 [3] Montes, R.H.; Marra, M.C.; Rodrigues, M.M.; Richter, E.M.; Muñoz, R.A.; Electroanalysis 2014, 26, 432. [4] Zhang, F.; Gu, S.; Ding, Y.; Zhang, Z.; Li, L.; Anal. Chim. Acta 2013, 770, 53. [5] Beitollahi, H.; Hamzavi, M.; Torkzadeh-Mahani, M.; Shanesaz, M.; Maleh, H. K. A.; Electroanalysis 2015, 27, 524. [6] Hua, L.; Han, H.; Zhang, X.; Talanta 2009, 77, 1654. [7] C. R. S. Matos, H. O. Souza Jr, T. B. Santana, L. P. M. Candido, F. G. C. Cunha, E. M. Sussuchi, I. F. Gimenez, Microchim. Acta 2017, 184, 1755. Figure 1

Synthesis of Hydrotalcite-Supported CdTe Semiconductor Nanocrystals for Electrochemical Detection of Ciprofloxacin

In this work, CdTe quantum dots (QDs) were controllably grown onto the surface of layered double hydroxide (LDH) aiming to develop a sensitive and selective method for the electrochemical detection of ciprofloxacin (CPX). Emission and absorption spectroscopy results as well as high-resolution transmission electron microscopy (HRTEM) images evidenced the formation of LDH/QD hybrid material. Unmodified carbon paste electrodes (CPE) as well as CPE chemically modified (MCPE) with native LDH and with the LDH/QD hybrid were prepared for CPX detection, revealing that MCPE-LDH/QD had the highest sensitivity for the detection of ciprofloxacin. Optimum detection conditions included a modifier dosage of 20% in MCPE, Britton-Robinson (BR) buffer (pH 6.0) as analytical medium, 300 s accumulation time and a scanning rate of 20 mV s-1. Linear current versus concentration curve was observed from 2.5 × 10-8-1.2 × 10-5 mol L-1 (coefficient of determination (R2) = 0.995), with sensitivity (limit of detection (LOD) = 4.2 × 10-8 mol L-1; limit of quantification (LOQ) = 1.3 × 10-7 mol L-1), precision (relative standard deviation (RSD) = 3.0%), accuracy (94.0%) and satisfactory selectivity in the presence of Zn2+, Fe2+, Cu2+, citric acid and ascorbic acid. Tests of CPX determination in commercial 500 mg ciprofloxacin tablets evidenced the applicability of the method.

Probing Absolute Electronic Energy Levels in Hg-Doped CdTe Semiconductor Nanocrystals by Electrochemistry and Density Functional Theory.

The absolute electronic energy levels in Hg-doped CdTe semiconductor nanocrystals (CdHgTe NCs) with varying sizes/volumes and Hg contents are determined by using cyclic voltammetry (CV) measurements and density functional theory (DFT) -based calculations. The electrochemical measurements demonstrate several distinct characteristic features in the form of oxidation and reduction peaks in the voltammograms, where the peak positions are dependent on the volume of CdHgTe NCs as well as on their composition. The estimated absolute electronic energy levels for three different volumes, namely 22, 119 and 187 nm(3) with 2.7±0.3 % of Hg content, show strong volume dependence. The volume-dependent shift in the characteristic reduction and oxidation peak potential scan can be attributed to the alteration in the energetic band positions owing to the quantum confinement effect. Moreover, the composition (Cd/Hg=98.3/1.7 and 97.0/3.0) -dependent alteration in the electronic energy levels of CdHgTe NCs for two different samples with similar volumes (ca. 124±5 nm(3) ) are shown. Thus obtained electronic energy level values of CdHgTe NCs as a function of volume and composition demonstrate good congruence with the corresponding absorption and emission spectral data, as well as with DFT-based calculations. DFT calculations reveal that incorporation of Hg into CdTe NCs mostly affects the energy levels of conduction band edge, whereas the valence band edge remains almost unaltered.

An effective and simple oxygen nanosensor made from MPA-capped water soluble CdTe nanocrystals

CdTe semiconductor nanocrystals (NCs) with 3-mercaptopropionic acid as the ligand exhibit a reversible response towards inter-switching oxygen and argon environments. The photoluminescence response is investigated at multiple oxygen concentrations, NC coverage and excitation intensities, in which all conditions exhibit full recovery upon exposure to flowing argon. The CdTe NC’s large surface-to-volume ratio results in high sensitivity towards oxygen molecules with significant photoluminescence quenching at a concentration of 40 ppm. This suggests a novel approach to the creation of simple, inexpensive and ultrasensitive oxygen nanosensors.

Controlled synthesis of CdTe nanocrystals for high performanced Schottky thin film solar cells

We report the synthesis of CdTe semiconductor nanocrystals (NCs) with multi-armed, rod and tetrapod shapes, developed by a facile solution process using a cadmium carboxylate as the precursor at moderate temperatures of 220–300 °C. It was found that the size and morphology of the CdTe NCs were related to synthesis parameters such as the reaction temperature, carboxyl chain length and carboxylic acid. Based on these CdTe NCs, photovoltaic cells (PVC) in simple Schottky diode configuration of ITO/CdTe/Al were fabricated. The performances of the CdTe NCs solar cells were found to strongly rely on the morphology and surface ligand of the CdTe NCs. The best device could show a power conversion efficiency (PCE) of 5.15% under AM 1.5G illumination at 100 mW cm−2, which is the highest efficiency of a CdTe NC-based Schottky solar cell reported to date. Notably, in comparison to the ITO/CdTe/LiF/Al device, the device configuration of ITO/CdTe/Al showed higher efficiency and better air-stability.

CdTe nanocrystals-enhanced chemiluminescence from peroxynitrous acid–carbonate and its application to the direct determination of nitrite

It was found that CdTe semiconductor nanocrystals (NCs) can induce a great sensitized effect on chemiluminescence (CL) emission from peroxynitrous acid (ONOOH)–Na 2CO 3 system. CL spectra, fluorescence (FL) spectra, and the quenching effect of reactive oxygen species were used to investigate the CL reaction mechanism. The CL intensity was proportional to the concentration of nitrite in the range from 0.05 to 50 μM. The detection limit ( S/ N = 3) was 0.024 μM and the relative standard deviation (RSD) for five repeated measurements of 0.5 μM nitrite was 4.2%. This method has been successfully applied to determine nitrite in well water samples with recoveries of 94.0–100.5%. This was the first work for direct (not inhibition effect) determination of analytes using semiconductor NCs-based CL sensor.

Influence of different stabilizers on the optical and nonlinear optical properties of CdTe nanoparticles

CdTe semiconductor nanocrystals were synthesized with three different stabilizers: Mercaptoacetic Acid (MAA), Mercaptopropionic Acid (MPA) and 2-Mercaptoethanol (ME) at pH ≈ 11.2 by wet chemical route using potassium tellurite and cadmium chloride as starting materials. The effect of capping agent on the preparation of these samples was evaluated using UV–Visible absorption and photoluminescence analysis. With the same reaction time but with different stabilizers, nanocrystals of different diameters were obtained. The average full width at half maximum of the photoluminescence spectra was about 69 nm which indicates that the monodispersity was quite good. The particle size was calculated by Debye–Scherrer equation from XRD data. Further characterization studies such as FT-IR and optical nonlinearity studies on the samples were carried out and the results are discussed.

Energy transfer with semiconductor nanocrystals

Forster (or fluorescence) resonant energy transfer (FRET) is a powerful spectroscopic technique to study interactions, conformational and distance changes, in hybrid nanosystems. Semiconductor nanocrystals, also known as colloidal quantum dots, are highly efficient fluorophores with a strong band-gap luminescence tuneable by size as a result of the quantum confinement effect. Starting from a short summary on the FRET formalism and on the basic properties of semiconductor nanocrystals, this Feature Article provides an overview of the major classes of hybrid FRET systems with semiconductor nanocrystals as at least one component. Systems under consideration include thin solid films containing differently sized semiconductor nanocrystals, solution-based complexes of differently sized semiconductor nanocrystals, nanocrystal-based bioconjugates, and hybrid structures of semiconductor and gold nanoparticles. We focus in particular on the directional energy transfer in layer-by-layer assembled multilayers of differently sized CdTe semiconductor nanocrystals and on the energy transfer from individual rod-like semiconductor CdSe/CdS nanoantennae to single dye molecules, which can be efficiently controlled by external electric fields leading to the realisation of the FRET optical switch.

CdTe nanocrystals sensitized chemiluminescence and the analytical application

It was found that the mixing of CdTe semiconductor nanocrystals (NCs) with luminol in the presence of KMnO 4 can induce a great sensitized effect on chemiluminescence (CL) emission. When the concentration of luminol, KMnO 4 and NaOH were fixed at 1 μM, 1 μM and 0.05 M, respectively, the most excellent performance can be obtained for the CdTe NCs sensitized CL. By means of CL and photoluminescence spectra, we suppose the enhanced CL signals resulted from the accelerated luminol CL induced by the oxidized species of CdTe NCs. Based on the finding, using thioglycolic acid-capped CdTe NCs as label and immunoglobulin G (IgG) as a model analyte, a CL immunoassay protocol for IgG content detection was developed. The strong inhibition effect of phenol compounds on luminol–KMnO 4–CdTe NCs CL system was also observed. All these findings demonstrated the possibility of semiconductor nanocrystals induced chemiluminescence to be utilized for more practical applications.

Facile one-pot preparation and functionalization of luminescent chitosan-poly(methacrylicacid) microspheres based on polymer–monomer pairs

In this paper, we present a facile and robust approach to synthesize multifunctionalorganic/inorganic composite microspheres with chitosan-poly(methacrylic acid)(CS-PMAA) shells and cadmium tellurium/iron oxide nanoparticle cores. Due to the strongelectrostatic interaction between the negatively charged nanoparticles and the protonatedCS polymers, the CS/nanoparticle complexes were utilized as templates for the subsequentpolymerization of methacrylic acid. The resulting composite microspheres withluminescence and magnetic properties have regular morphologies and narrow sizedistributions. In contrast to previous reports, this route was based on a one-pot strategywithout the aid of surfactants, organic solvent, or polymerizable ligands in aqueoussolution. The encapsulated CdTe semiconductor nanocrystals inside the microspheresexhibited strong and stable photoluminescence properties in the pH range 5.0–11.0.When the pH was adjusted below 4, the photoluminescence decreased sharply andeven quenched completely. However, the weakened fluorescence emission could berecovered to some degree upon an increase of pH above 5. Additionally, when bothFe3O4 and CdTe nanoparticles were encapsulated within CS-PMAA microspheres, the magneticcontent of the microspheres could be efficiently controlled by tuning the feeding molar ratioof MAA monomers and glucosamine units of CS. From the preliminary attempts, it wasfound that the multifunctional microspheres as imaging agents could improvethe rate and extent of cellular uptake under short-term exposure to an appliedmagnetic field, and so exhibit a great potential as bioactive molecule carriers.

A facile and green preparation of high-quality CdTe semiconductor nanocrystals at roomtemperature

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth ofsemiconductor nanocrystals (cadmium telluride) instead of additional energy, which wasapplied to the synthesis of high-quality CdTe nanocrystals at room temperature andambient conditions within several hours. Under this mild condition the mercapto stabilizerswere not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrowand uniform distribution over the largest possible range. The CdTe nanocrystals(photoluminescence emission range of 530–660 nm) synthesized in this way hadvery good spectral properties; for instance, they showed high photoluminescencequantum yield of up to 60%. Furthermore, we have succeeded in detecting the livingBorrelia burgdorferi of Lyme disease by its photoluminescence image using CdTenanocrystals.

Luminescent CdTe and CdSe Semiconductor Nanocrystals: Preparation, Optical Properties and Applications

We demonstrate herein a "green" pathway for the formation of a gold nanocomposite using the cuttlebone-derived organic matrix. The gold nanocomposite is achieved through the first exposure of the organic matrix to HAuCl4 solution at room temperature and its subsequent heating at 80 degrees C. The process results in the formation of a macro porous gold nanocomposite consisting of gold nanoparticles embedded in the cuttlebone-derived organic matrix background, which shows the characteristic plasma absorption of gold nanostructures. UV-vis-IR spectrophotometer and transmission electron microscope (TEM) were used to characterize the gold nanocomposite and trace the formation process. A highlight of the research is that we adopted a nontoxic and renewable reagent of cuttlebone-derived organic matrix, which functioned as the reducing reagent, stabilizer and scaffold for the synthesis of gold nanoparticles.

Luminescent CdTe and CdSe Semiconductor Nanocrystals: Preparation, Optical Properties and Applications

The novel optical and electrical properties of luminescent semiconductor nanocrystals are appealing for ultrasensitive multiplexing and multicolor applications in a variety of fields, such as biotechnology, nanoscale electronics, and opto-electronics. Luminescent CdSe and CdTe nanocrystals are archetypes for this dynamic research area and have gained interest from diverse research communities. In this review, we first describe the advances in preparation of size- and shape-controlled CdSe and CdTe semiconductor nanocrystals with the organometallic approach. This article gives particular focus to water soluble nanocrystals due to the increasing interest of using semiconductor nanocrystals for biological applications. Post-synthetic methods to obtain water solubility, the direct synthesis routes in aqueous medium, and the strategies to improve the photoluminescence efficiency in both organic and aqueous phase are discussed. The shape evolution in aqueous medium via self-organization of preformed nanoparticles is a versatile and powerful method for production of nanocrystals with different geometries, and some recent advances in this field are presented with a qualitative discussion on the mechanism. Some examples of CdSe and CdTe nanocrystals that have been applied successfully to problems in biosensing and bioimaging are introduced, which may profoundly impact biological and biomedical research. Finally we present the research on the use of luminescent semiconductor nanocrystals for construction of light emitting diodes, solar cells, and chemical sensors, which demonstrate that they are promising building blocks for next generation electronics.

Comparison of Brightness of Emitting Semiconductor Nanocrystals with That of Rare-Earth Phosphor

A method was developed to compare the brightness of newly developed thin films with dispersed photoluminescent CdTe semiconductor nanocrystals (NCs) at an ultimately high concentration (ca. 0.01 M) with that of a typical commercial rare-earth phosphor (Y2O2S:Eu). We have found it is reasonable to compare their brightness under conditions of the same sample thickness, excitation intensity, and wavelength. At the weak-excitation limit, the brightness of the new films was about 30 times higher. This higher brightness is due to the higher concentration and emission efficiency of NCs, and the larger absorption cross section per unit volume of NCs. The difference in the brightness increases with the excitation intensity because rare-earth phosphors exhibit a strong saturation phenomenon due to their long emission decay time. Because these films are efficiently excited by UV–blue diodes, the power of which is steadily increasing, they will become more applicable in future.

Investigation into the Growth Kinetics of CdTe Nanocrystals in Germanophosphate Glasses by Optical Spectroscopy

The evolution of the absorption, photoluminescence, and Raman spectra of germanophosphate glasses containing CdTe semiconductor nanocrystals is investigated. It is shown that two stages can be distinguished in the evolution of the absorption spectra during isothermal annealing. At the first stage, the annealing is accompanied by the appearance of the absorption peak. At the second stage, an increase in the heat treatment time leads to a shift in the absorption peak toward the short-wavelength range. The dependence of the mean size of nanocrystals is calculated within the tight-binding model. It is revealed that, at the second stage, the dependence of the mean size of CdTe nanocrystals formed in the germanophosphate matrix can be described by the relationship R ∼ t0.12−0.16. This dependence is confirmed by the photoluminescence and Raman spectroscopic data (on the position of the Lamb mode).

Synthesis of CdSe and CdTe Nanocrystals without Precursor Injection

With high quality and in high yield: The synthesis presented here affords CdSe and CdTe semiconductor nanocrystals without the need of a precursor injection. It allows the detailed control of the size and shape of the nanocrystals, as can be seen from the tetrahedral CdSe nanocrystals that have been prepared (TEM image). The method is suitable for industrial-scale preparations.

Luminescent Polymer Microcapsules Addressable by a Magnetic Field

The simultaneous encapsulation of both luminescent semiconductor and magnetic oxide nanoparticles in polymer microcapsules is demonstrated for the first time. Highly luminescent CdTe semiconductor nanocrystals serve as luminescent markers, while magnetic Fe3O4 nanoparticles allow external manipulation of the capsules by magnetic field. The method introduced is general enough to allow the fabrication of different types of multifunctional capsules in a similar way. The use of multifunctional water-compatible capsules introduced in this paper for the controlled release and directed drug delivery in biological systems is envisaged.

Electrochemical synthesis of CdTe nanocrystal/polypyrrole composites for optoelectronic applications

Electrochemical polymerisation has been found to be a convenient method for the synthesis of a thin film composite of a conducting polymer (polypyrrole) and strongly luminescent CdTe semiconductor nanocrystals. Optimal conditions (relatively low anodic potential, neutral pH, aqueous solution) for the synthesis of uniform high-quality films combining the mechanical, electrical and optical properties of the polymer with the luminescence properties of the semiconductor nanocrystals have been established. It has been shown that insertion of the CdTe nanoparticles into the polypyrrole matrix leads to a significant increase in their electroluminescence quantum efficiency.