Bare CdTe Research Articles

Particle swarm optimization for performance enhancement of cadmium telluride thin film solar cells by embedded nano-grating structures with a plasmonic metal coating layer

As the demand for energy in world is increasing rapidly and there is pursuit for renewable energy sources which is cheap, easy to generate and requires low maintenance, solar energy is a top contender. The world is in dire need of photovoltaic solar cells that can aid in keeping up with the hiking energy demands. However, thin film solar cells (TFSCs) which are developed for cost effectivity, suffer in performance due to reduced thickness. Therefore, this computational study uses Finite-Difference Time-Domain (FDTD) and delves into the scope of using a 1-D nano-grating structure embedded into absorbing layer of cadmium telluride TFSC to enhance the optoelectronic performance. A unique nano-grating structure with SiO2 at its core and aluminium coating aims to enhance the performance of CdTe TFSC with cost effectivity and ease of fabricability as the main motifs. Additionally, an evolutionary computational technique, Particle Swarm Optimization (PSO), was used to determine the optimal parameters of nano-gratings on CdTe TFSCs, i.e., nano-grating height, angle, duty cycle, aluminium coating thickness and grating substrate thickness. The PSO algorithm resulted in a nano-grating structure that yielded an efficiency increase of 52.86% and increase in short-circuit current density of 25.45% with respect to bare CdTe TFSCs. Subsequently, the performance of the optimal nano-grating structure was also observed to be insensitive to variation of wide range of incidence angle of light, a key feature preferred for versatile application of TFSCs.

Carbon encapsulated CdTe nanorods to execute the enhanced and photo corrosion free hydrogen production

We present carbon-encapsulated CdTe nanorods synthesized through a well-established hydrothermal method. The impact of varying weight percentages of carbon on CdTe nanorods has been explored. XRD, HR-TEM, XPS, Raman and UV-Vis characterization techniques are used to examine the physicochemical and optical properties of prepared compounds. The loading of the carbon layer can be regulated by varying the quantity of sucrose utilized during the synthesis process. The optimized photocatalyst exhibits a superior rate of hydrogen evolution at 247.7 mmol. h−1. g−1cat compared to bare CdTe nanorods. Here, the carbon layer serves a dual purpose as a photocorrosion inhibitor and facilitates electron tunneling for surface reactions. This combined effect of carbon on CdTe is responsible for the observed improvement in the hydrogen evolution rate. As the loading of carbon varies, the activity is aligning closely with the light penetration effect in photocatalysis. Furthermore, we investigated the durability of the optimized photocatalyst, revealing that it retains 89 % of its initial activity even after five cycles. After the activity experiments, essential characterizations such as XRD, Raman and XPS were also analyzed, and the solar to H2 conversion efficiency was computed.

Finely-Tuning Chemiluminescent Color of CdTe Nanocrystals and Its Application for Near-Infrared Semi-Automatic Immunoassay.

Chemiluminescence (CL), especially commercialized CL immunoassay (CLIA), is normally performed within the eye-visible region of the spectrum by exploiting the electronic-transition-related emission of the molecule luminophore. Herein, dual-stabilizers-capped CdTe nanocrystals (NCs) is employed as a model of nanoparticulated luminophore to finely tune the CL color with superior color purity. Initialized by oxidizing the CdTe NCs with potassium periodate (KIO4), intermediates of the reactive oxygen species (ROS) tend to charge CdTe NCs in both series-connection and parallel-connection routes and dominate the charge-transfer CL of CdTe NCs. The CdTe NCs/KIO4 system can exhibit color-tunable CL with the maximum emission wavelength shifted from 694 nm to 801 nm, and the red-shift span is over 100 nm. Both PL and CL of each of the CdTe NCs are bandgap-engineered; the change in the NCs surface state via CL reaction enables CL of each of the CdTe NCs to be red-shifted for ∼20 nm to PL, while the change in the NCs surface state via labeling CdTe NCs to secondary-antibody (Ab2) enables CL of the CdTe NCs-Ab2 conjugates to be red-shifted for another ∼20 nm to bare CdTe NCs. The CL of CdTe753-Ab2/KIO4 is ∼791 nm, which can perform near-infrared CL immunoassay and semi-automatically determined procalcitonin (PCT) on commercialized in vitro diagnosis (IVD) instruments.

CdTe/CdS Core–Shell Quantum Dots: Synthesis and Applications as a Heavy Metal Ion's Fluorescence Sensor and Photocatalyst for Photodegradation of Organic Dyes

Herein, a simple method for the growth of the CdS shell around CdTe QDs and the formation of the CdTe/CdS core–shell structure is proposed. The synthesized QDs are characterized using Raman, Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), and UV–vis analyses. XRD patterns confirm the formation of a core–shell‐type structure and particle sizes, lattice strain (ε), and displacement density (δ) are calculated using Williamson–Hall (W–H) and Williamson–Smallman (W–S) approaches. Obtained results show that the CdTe/CdS QDs are spherical with an average crystal size about 5.41 nm. In this work, derivation of absorption spectrum fitting (DASF) is used for the determination of the optical bandgap of the prepared QDs. Prepared CdTe/CdS QDs are applied for the detection of the heavy metal ions and photodegradation of the different organic dyes in aqueous media. The prepared QDs show good performance for the detection of mercury ions (Hg2+) in water with superior selectivity and for photodegradation of the methylene orange (MO) under UV light. The comparison of the obtained results for CdTe/CdS with bare CdTe QDs shows that the core–shell CdTe/CdS QDs have higher sensitivity and enhanced photocatalyst properties compared to the CdTe QDs.

CdTe surface passivation by electric field induced at the metal-oxide/CdTe interface

In this study, three kinds of metal oxide (MOs), namely, V2O5, Al2O3 and NiO, were deposited on CdTe thin films to study possible passivation effect on the CdTe surface. Time-resolved photoluminescence (TRPL) measurements were carried out to study the minority carrier lifetime of the MO-coated CdTe and bare CdTe. The results showed that the TRPL decay curves were consisted of a fast and a slow decay process for all samples. For both the bare and NiO-coated CdTe surface, the fast and the slow decay lifetimes were found to be 0.5 and 1.0 ns. While for the Al2O3- and V2O5-coated CdTe, the fast decay lifetime was 0.6 and 0.7 ns, and the slow decay lifetime was 2.1 and 2.4 ns, respectively. CdTe surface defect states with high surface recombination velocity, ~106 cm/s, were responsible for the fast decay. The CdTe surface was effectively passivated by a 3-nm-thick V2O5 or Al2O3 coating layer. The simulation and experimental results indicated that the passivation was ascribed to the electric field effect induced by negative fixed charges in V2O5 and Al2O3.

Novel biomolecule-capped CdTe nanoparticles for highly efficient photodegradation of methyl orange dye under visible-light irradiation

In this study, L-arginine-capped cadmium telluride (CdTe) nanoparticles (NPs) were successfully prepared using the hydrothermal process. The formation, morphology, and physicochemical properties of the prepared samples were successfully characterized using different analytical techniques, such as X-ray diffraction (XRD), Fourier transforms infrared (FTIR), High-resolution transmission electron microscopy (HRTEM), Ultraviolet–visible spectroscopy (UV–Visible) and Photoluminescence spectroscopy (PL). The photocatalytic activity of the prepared samples was evaluated by the degradation of methyl orange (MO) dye under visible-light. It was observed that 86.3% MO dye removal efficiency was achieved over L-arginine-capped CdTe NPs, which was 1.6 times higher than that of the bare CdTe NPs. Interestingly, the L-arginine-capped CdTe photocatalyst was recycled in four consecutive runs without significant activity loss.

Plasmon-Assisted Suppression of Surface Trap States and Enhanced Band-Edge Emission in a Bare CdTe Quantum Dot.

Colloidal quantum dots have emerged as a versatile photoluminescent and optoelectronic material. Limitations like fluorescence intermittency, nonradiative Auger recombination, and surface traps are commonly addressed by growing a wide-band-gap shell. However, the shell isolates the excitonic wave function and reduces its interaction with the external environment necessary for different applications. Furthermore, their long emission lifetime hinders their use in high-speed optoelectronics. Here, we demonstrate a high degree of control on the photophysics of a bare core CdTe quantum dot solely by plasmon coupling, showing that more than 99% of the surface defect-state emission from a trap-rich quantum dot can be quenched. Moreover, the band-edge state excitonic and biexcitonic emission rates are Purcell enhanced by 1460- and 613-fold, respectively. Our findings show how plasmon coupling on bare quantum dots could make chemical approaches developed for improving their optical properties unnecessary, with implications for nanoscale lasers, light-emitting devices, solar cells, and ultrafast single-photon sources.

Enhanced fluorescence properties of type-I and type-II CdTe/CdS quantum dots using porous silver membrane

This paper reports the metal-induced fluorescence property on the CdTe/CdS core/shell quantum dots (QDs), which exhibit the systematic band-gap transition from type-I to type-II with increasing shell thickness, near porous silver membrane by using time-resolved fluorescence lifetime imaging microscopy (FLIM). The results revealed that notable fluorescence enhancement came from the closed location to the cavity of the porous silver metal due to an increase in the local electromagnetic fields at the cavity. In the cases of the type-II CdTe/CdS QDs, interestingly, multiple exciton generation can be an additional factor for the lifetime reduction and fluorescence amplification compared to the type-I QDs. Without CdS shell, the strong interaction between the bare core CdTe QDs and silver caused emission quenching.

A novel method for fabricating hybrid biobased nanocomposites film with stable fluorescence containing CdTe quantum dots and montmorillonite-chitosan nanosheets

A method was presented for fabricating the fluorescent nanocomposites containing CdTe quantum dots (QDs) and montmorillonite (MMT)-chitosan (CS). MMT-CS/CdTe QDs nanocomposites were prepared via a simple, versatile and robust approach combination of covalent and electrostatic assembly methods (Scheme 1). The negatively charged MMT was initially modified with positively charged CS through electrostatic assembly, followed by incorporation of CdTe-QDs into the MMT-CS nanosheets by covalent connections between the amino groups of CS and the carboxylic acid groups of thioglycollic acid (TGA). The X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and the FTIR were used to prove the QDs have intercalated into the MMT-CS matrix. The fluorescence emission spectra showed that the MMT-CS/CdTe QDs nanocomposites had the best fluorescence intensity compared with the bare CdTe QDs and CS-QDs.

Strongly confining bare core CdTe quantum dots in polymeric microdisk resonators

We report on a simple route to the efficient coupling of optical emission from strongly confining bare core CdTe quantum dots (QDs) to the eigenmodes of a micro-resonator. The quantum emitters are embedded into QD/polymer sandwich microdisk cavities. This prevents photo-oxidation and yields the high dot concentration necessary to overcome Auger enhanced surface trapping of carriers. In combination with the very high cavity Q-factors, interaction of the QDs with the cavity modes in the weak coupling regime is readily observed. Under nanosecond pulsed excitation the CdTe QDs in the microdisks show lasing with a threshold energy as low as 0.33 μJ.

Reduced graphene oxide and CdTe nanoparticles co-decorated TiO2 nanotube array as a visible light photocatalyst

TiO2 nanotube array (TiO2 NT) was co-decorated by reduced graphene oxide (RGO) and CdTe nanoparticles (NPs) through a simple one-step electrodeposition process. RGO film was formed on the top surface of TiO2 NT and CdTe NPs homogeneously dispersed within the RGO sheets and on the inner/outer walls of TiO2 NT. Resulting from the synergetic effect of RGO and CdTe, the photocatalytic activity of the ternary RGO/CdTe–TiO2 NT photocatalyst far exceeded those of bare TiO2 NT, RGO-TiO2 NT, and CdTe–TiO2 NT photocatalysts in the degradation of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) under simulated solar light or visible light irradiation. After 180-min UV–Vis (or visible light) irradiation, almost 100 % (or 96 %) 2,4-D removal efficiency was achieved on RGO/CdTe–TiO2 NT, much higher than 42 % (or 2 %) on bare TiO2 NT, 58 % (or 10 %) on RGO–TiO2 NT, and 52 % (or 41 %) on CdTe–TiO2 NT. This study will inspire better design of advanced photocatalysts with high visible-light photocatalytic activity.

Parallel comparative studies on the toxic effects of unmodified CdTe quantum dots, gold nanoparticles, and carbon nanodots on live cells as well as green gram sprouts

By using confocal fluorescence microscopy and direct visualization, a parallel comparative investigation has been systematically made on the relative toxicity of three common nanomaterials, such as unmodified CdTe quantum dots (QDs), Au nanoparticles (Au NPs) and carbon nanodots (C-dots), to live cells as well as green gram sprouts. Bare CdTe QDs exert the most toxic effect on a variety of cell lines (HeLa, MCF-7, NIH/3T3 cells) as well as live plants (green gram sprouts). For cells, this toxic effect leads to the partial death of cells, the decrease of cell metabolic activity, the shrinkage of cells, the breakage of chromatin, the damage of cell membrane integrity, and the fragmentation of mitochondria; for green gram sprouts, the presence of CdTe QDs markedly inhibits their growth. Moreover, the toxic behaviors of CdTe QDs are dose- and time-dependent. Under the same conditions, Au NPs only decrease the metabolic activity of cells to a small extent, and do not affect the appearance of cellular/subcellular structures and the plant growth; interestingly, C-dots exert no obvious toxicity to both live cells and the growth of green gram sprouts, showing good biocompatibility. These parallel comparative studies clearly reveal that the relative toxicity of the three nanomaterials in their native forms is bare CdTe QDs⪢Au NPs>C-dots, whose IC50 values for normal NIH/3T3 cells are 0.98μg/mL, 62μg/mL, and >250μg/mL, respectively. This quantitative information is of great importance for right choice of the nanomaterials in their practical applications.

Optimization of Quantum Dots system of CdTe and Transferrin by Capillay Electrophoresis-Laser Inductive Fluorescence and Verification in Cell Labeling

Abstract Capillary electrophoresis-laser inductive fluorescence (CE-LIF) was used to characterize the active effect difference of coupling agent N -hydroxysulfo-succinimide (NHS) and the mixture of NHS and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimides hydrochloride (EDC) on quantum dots CdTe, and to optimize the conditions of CdTe and transferring (Trf) coupling. The labeling effect of CdTe-Trf and CdTe-BSA complex as well as bare CdTe in Hela cell was compared. The results demonstrated that the property of CdTe activated by NHS was better than that of the mixture of EDC-NHS. When 12.5, 31.2 and 40.6 μM Trf were used to couple CdTe respectively, the resultant of CdTe with 31.2 μM Trf optimized by CE-LIF showed the best labeling on Hela. The CdTe-Trf resultant labeled Hela rapidly on the surface when they incubated at 4 °C for 20 min, and transferred into Hela when they incubated at 37 °C for 7 h, which manifested the CdTe-Trf resultant has biological function. The CdTe-Trf can recognize and bind the Trf receptor on cell membrane specifically and enter Hela, while CdTe-BSA cannot recognize Hela specifically and bare CdTe cannot label on cell.

Modulated exciton-plasmon interactions in Au-SiO_2-CdTe composite nanoparticles

Well-defined Au-SiO(2)-CdTe composite nanoparticles were synthesized via a multistep chemical approach in water solution to gain insight into the interaction between metal and semiconductor nanostructures. Photoluminescence measurement reveals that the fluorescence of CdTe quantum dots (QDs) in this composite with optimized SiO(2) thickness (4 nm) has over ten times enhancement compared with that of bare CdTe QDs. The considerable fluorescence enhancement of CdTe QDs is attributed to the surface plasmon resonance, which is further confirmed by the lifetime measurement. The enhanced fluorescence can be used to improve the performance of CdTe QDs as fluorescence probe and may find potential applications in biolabeling.

Electrostatic assembly of CdTe quantum dots with different charged ligands into TiO2 porous film for solar cells

We have demonstrated an approach for the electrostatic assembly of CdTe quantum dots (QDs) with different charged ligands as sensitizers, achieving high coverage and good dispersion in TiO2 porous films. The CdTe QD-sensitized TiO2 porous films were subjected to thermal annealing in a high vacuum chamber to remove the ligand linker, resulting in the formation of direct heterojunctions between the bare CdTe QDs and TiO2 for a favorable charge transfer. The as-received CdTe QD-sensitized TiO2 porous films were employed as photoanodes for quantum dot-sensitized solar cells (QSSCs), and the photocurrent density reached as high as 4.69 mA/cm2 under a standard illumination condition of simulated AM 1.5G (100 mW/cm2).

Comparison of cytotoxicity and expression of metal regulatory genes in zebrafish (Danio rerio) liver cells exposed to cadmium sulfate, zinc sulfate and quantum dots

Recent advances in the ability to manufacture and manipulate materials at the nanometer scale have led to increased production and use of many types of nanoparticles. Quantum dots (QDs) are small, fluorescent nanoparticles composed of a core of semiconductor material (e.g. cadmium selenide, zinc sulfide) and shells or dopants of other elements. Particle core composition, size, shell, and surface chemistry have all been found to influence toxicity in cells. The aim of this study was to compare the toxicities of ionic cadmium (Cd) and zinc (Zn) and Cd- and Zn-containing QDs in zebrafish liver cells (ZFL). As expected, Cd(2+) was more toxic than Zn(2+), and the general trend of IC50-24 h values of QDs was determined to be CdTe < CdSe/ZnS or InP/ZnS, suggesting that ZnS-shelled CdSe/ZnS QDs were more cytocompatible than bare core CdTe crystals. Smaller QDs showed greater toxicity than larger QDs. Isolated mRNA from these exposures was used to measure the expression of metal response genes including metallothionein (MT), metal response element-binding transcription factor (MTF-1), divalent metal transporter (DMT-1), zrt and irt like protein (ZIP-1) and the zinc transporter, ZnT-1. CdTe exposure induced expression of these genes in a dose dependent manner similar to that of CdSO4 exposure. However, CdSe/ZnS and InP/ZnS altered gene expression of metal homeostasis genes in a manner different from that of the corresponding Cd or Zn salts. This implies that ZnS shells reduce QD toxicity attributed to the release of Cd(2+), but do not eliminate toxic effects caused by the nanoparticles themselves.

Resonantly enhanced optical nonlinearity in hybrid semiconductor quantum dot – metal nanoparticle structures

The optical nonlinearity of hybrid structures composed of CdTe quantum dots and periodical particle array of gold is studied using Z-scan method. The optical nonlinearity is dramatically affected by the interaction between exciton in CdTe quantum dots and surface plasmons in Au periodical particle array. When the Au surface plasmon is tuned to be in resonance with the exciton transition in CdTe quantum dots, the largest nonlinear refractive index and the smallest two-photon absorption coefficient, n2 = −0.53 cm2/GW and β = 25 cm/GW, which are about 8 times larger and 50 times smaller than that of bare CdTe quantum dots, can be achieved.

Solution–liquid–solid growth of high-density CdTe nanowires on glass substrates and core/shell structure formation

High-density CdTe nanowires have been for the first time grown on soda-lime glass substrates via solution–liquid–solid (SLS) approach. ZnSe nanocrystals were synthesized viaTOP/TOPO route and coated on the CdTe nanowires to form CdTe/ZnSe core/shell structures. CdTe/ZnSe nanowires showed enhanced photoluminescence emission compared to bare CdTe nanowires.

Aqueous Synthesis of Highly Luminescent CdTe/CdS/ZnS Core-Shell-Shell Quantum Dots with Biocompatibility

CdTe/CdS/ZnS core-shell-shell (CSS) quantum dots (QDs) were synthesized in aqueous solution via water-bathing combined hydrothermal method using L-cysteine (L-Cys) as a stabilizer. This method possesses both the advantages of water-bathing and hydrothermal methods, and thus can prepare CSS QDs with markedly reduced synthesis time than previously reported methods. The as-prepared QDs display a higher fluorescent intensity than bare CdTe or CdTe/CdS. After co-cultured with yeast at different growth phase, the as-prepared L-Cys capped CdTe/CdS/ZnS QDs showed much less toxicity than the other CdTe or CdTe/CdS QDs. Our results demonstrate that the CSS QD would have a promising potential in fields of bio-labeling and cell imaging.

Antimicrobial activity and cellular toxicity of nanoparticle–polymyxin B conjugates

We investigate the antimicrobial activity and cytotoxicity to mammalian cells of conjugatesof the peptide antibiotic polymyxin B (PMB) to Au nanoparticles and CdTe quantumdots. Au nanoparticles fully covered with PMB are identical in antimicrobialactivity to the free drug alone, whereas partially-conjugated Au particles showdecreased effectiveness in proportion to the concentration of Au. CdTe–PMBconjugates are more toxic to Escherichia coli than PMB alone, resulting in a flatteningof the steep PMB dose–response curve. The effect is most pronounced at lowconcentrations of PMB, with a greater effect on the concentration required toreduce growth by half (IC50) than on the concentration needed to inhibit allgrowth (minimum inhibitory concentration, MIC). The Gram positive organismStaphylococcus aureus is resistant to both PMB and CdTe, showing minimal increasedsensitivity when the two are conjugated. Measurement of reactive oxygen species(ROS) generation shows a significant reduction in photo-generated hydroxyl andsuperoxide radicals with CdTe–PMB as compared with bare CdTe. There is acorresponding reduction in toxicity of QD–PMB versus bare CdTe to mammalian cells,with nearly 100% survival in fibroblasts exposed to bactericidal concentrations ofQD–PMB. The situation in bacteria is more complex: photoexcitation of theCdTe particles plays a small role in IC50 but has a significant effect on the MIC,suggesting that at least two different mechanisms are responsible for the antimicrobialaction seen. These results show that it is possible to create antimicrobial agentsusing concentrations of CdTe quantum dots that do not harm mammalian cells.