Narrow Results

Excitonic effects are observed in the optical absorption and photoluminescence of strongly confined CdS quantum dots embedded in the polymer matrix. CdS nanoparticles of different crystallite sizes have been prepared by chemical route with polymer as a host material. The CdS nanocomposite film was made up of particle smaller than 5 nm and shows a composite band gap up to 3.2 eV, whereas the band gap for bulk hexagonal CdS is about 2.42 eV. Photoluminescence spectra show a strong emission band corresponding to electron–hole recombination and a weak band due to defect emission. The decrease of particle size was monitored from the U-V visible absorption measurement as well as photoluminescence, which suffered blue shift with decrease in particle size. The particle size and surface morphology were also analyzed by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM).

The optical spectral band positions and spin-Hamiltonian parameters (g factors g_‖, g_⊥ and zero-field splitting D) of CdS: Ti²⁺ and CdSe: Ti²⁺ crystals are calculated from the complete diagonalizaion (of energy matrix) method based on a two-spin-orbit parameter model for 3d² ions in trigonal symmetry. In the model, both the contribution to spin-Hamiltonian parameters due to the spin-orbit parameter of central 3d² ions and that of ligand ions are included. The crystal field parameters used in the calculations are obtained from the superposition model which enables correlation of the optical and EPR spectral data with the defect structure of the studied paramagnetic impurity centers in crystals. From the calculations, the defect structures of Ti²⁺ centers in CdS: Ti²⁺ and CdSe: Ti²⁺ are acquired, the signs of zero-field splittings D are suggested, and the optical band positions and spin-Hamiltonian parameters are explained. The results are discussed.

Cadmium Sulphide (CdS) thin films with different thicknesses were prepared by pulsed laser deposition technique using Nd:YAG laser with wavelength 1064 nm. AC electrical conductivity was studied in the frequency range 100–1000 KHz as a function of temperature. AC conductivity increased with increasing the frequency. The values of the activation energy of the AC conduction were calculated for CdS thin films of different thicknesses at various frequencies. The dielectric constant and dielectric loss were investigated as a function of temperature at different frequencies.

In this paper, we give a microscopic view concerning influence of the growth conditions on the physical properties of nanocrystals (NCs) thin films made of CdS, prepared using chemical bath deposition CBD technique. We show a crystalline phase transformation of CdS NCs from hexagonal wurtzite (W) structure to cubic zincblende (ZB) when the growth conditions change, particularly the solution pH values. This effect was confirmed using X-ray diffraction (XRD), transmission electron microscopy (TEM), optical absorption and photoluminescence (PL) measurements. The optical absorption spectra allow calculation of the bandgap value, $E_g$, where significant increase $\sim$200 meV in the CdS bandgap when transforming from Hexagonal to Cubic phase was found.

Formation energies of cadmium sulfide clusters are calculated with the help of density functional theory. The investigated structures include clusters that represent the CdS three main phases, wurtzite, zincblende and rock-salt. The investigation includes electronic, vibrational and thermal properties. CdS clusters are represented by wurtzoids, diamondoids and cuboids for the three phases, wurtzite, zincblende and rock-salt, respectively. The energy gap of the largest investigated molecules approaches that of bulk experimental 2.42 eV. The calculated longitudinal optical (LO) vibrational mode is 304.2 cm${}^{-1}$ which is in good agreement with the experimental bulk value of 305 cm${}^{-1}$. To calculate Gibbs free energy, enthalpy and entropy of formation for the clusters, we redefined these quantities so that they represent the difference between the CdS formation energy and their constitutes Cd and S clusters energy. The calculated Gibbs free energy of formation, enthalpy and entropy of the investigated clusters approach that of bulk. Wurtzoids are more stable than diamondoids and cuboids with the release of more heat as deduced from their cluster Gibbs energy and enthalpy of formation. The entropy of clusters is dependent on the size of the cluster. The present method draws a relation between known solid state phases and small cluster calculations.

This paper deals with an investigation on the photoluminescence (PL) properties of PP+PbS/CdS nanocomposites at different temperatures ($100^{\circ }\mathrm{\text{C}}$, $120^{\circ }\mathrm{\text{C}}$ and $140^{\circ }\mathrm{\text{C}}$) under vacuum. The optical bandgap was calculated on the basis of the spectra of UV absorption and it was shown that after thermal treatment the nanocomposites optical bandgap changed. The change has been attributed to the modification of the upper molecular structure of the polymer matrix due to the thermal process. The luminescence spectra of nanocomposites before and after thermal treatment at different temperatures ($100^{\circ }\mathrm{\text{C}}$, $120^{\circ }\mathrm{\text{C}}$ and $140^{\circ }\mathrm{\text{C}}$) under vacuum were also measured and discussed. A very high luminescence intensity was observed after thermal treatment at $100^{\circ }\mathrm{\text{C}}$ temperature. This was attributed to the luminescent centers’ increase and the optimal structure formation.

In this work, we study the influence of the temperature on the mechanism of current transfer in the reverse branch of the current–voltage (I–V) characteristics of n-CdS/p-CdTe heterostructures. The study of the heterostructure, using the technique of on energy-dispersive X-ray analysis, showed that a layer of CdS_xTe${}_{1-x}$ is formed at the boundary of the heterojunction with a varying composition, being equal $x\approx 0.48$ from the side of CdS and $x\approx 0.02$ from the CdTe side. In the studied range of the temperatures and bias voltage, the current-voltage characteristics are described well by a power law $J=A{V}^{\alpha }$, where the exponent $\alpha$ changes with the temperature and voltage. Under the influence of the temperature and charge carrier concentration, the mechanism of current transfer in the structure changes from exclusion ($\alpha \approx 0.5$) to ohmic ($\alpha \approx 1$), and then goes to injection ($\alpha \approx 2$). The inhomogeneous intermediate CdS_xTe${}_{1-x}$i-layer at the boundary of the n-CdS/p-CdTe heterostructure is characterized by the presence of metastable states that rearrange at high temperatures and certain charge carrier concentrations. As a result of this, the exclusion slows down and electrons are injected from the rear molybdenum contact.

Well-defined CdS branched nanorod arrays on ITO glass were fabricated via a facile one-step hydrothermal approach in large scale employing cadmium sulfide and thiourea as starting agents. Structural and morphological evolutions of CdS branched nanorod arrays were studied by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A formation mechanism of the hierarchical structure via this one-step synthesis was tentatively studied by investigating the reaction time. Tree-like nanostructures can also be obtained at relative higher reaction temperatures. As CdS can directly grow on transparent conductive substrate, the product obtained here should have potential applications in optoelectric devices such as solar cells and light sources.

Cadmium sulfide (CdS) and aluminum-doped zinc oxide (Al:ZnO) thin films are used as buffer layer and front window layer, respectively, in thin film solar cells. CdS and Al:ZnO thin films were produced using chemical bath deposition (CBD) and sol–gel technique, respectively. For CBD CdS, the effect of bath composition and temperature, dipping time and annealing temperature on film properties was investigated. The CdS films are found to be polycrystalline with metastable cubic crystal structure, dense, crack-free surface morphology and the crystallite size of either few nanometers or 12–17 nm depending on bath composition. In case of CdS films produced with 1:2 ratio of Cd and S precursors, spectrophotometer studies indicate quantum confinement effect, owing to extremely small crystallite size, with an increase in E_g value from 2.42 eV (for bulk CdS) to ~ 3.76 eV along with a shift in the absorption edge toward ~ 330 nm wavelength. The optimum annealing temperature is 400°C beyond which film properties deteriorate through S evaporation and CdO formation. On the other hand, Al:ZnO films prepared via spin coating of precursor sols containing 0.90–1.10 at.% Al show that, with an increase in Al concentration, the average grain size increases from 28 nm to 131 nm with an associated decrease in root-mean-square roughness. The minimum value of electrical resistivity, measured for the films prepared using 0.95 at.% Al in the precursor sol, is ~ 2.7 × 10^-4 Ω ⋅ cm. The electrical resistivity value rises upon further increase in Al doping level due to introduction of lattice defects and Al segregation to the grain boundary area, thus limiting electron transport through it.

Cube-shaped CdS nanoparticles have been successfully prepared by a sonochemical method in an oil-in-water microemulsion. The product was characterized by using techniques including X-ray powder diffraction, high-resolution transmission electron microscopy, energy-dispersive X-ray analysis and UV-visible absorption spectroscopy. This microemulsion system in the presence of high-intensity ultrasound irradiation provides special conditions for the nucleation and growth of the CdS nanoparticles.

Materials such as CdS and CdSe inorganic nanoparticles have photoluminescence. Sodium oleate has been used as effective stabilizers for the synthesis of CdS and CdSe nanoparticles in water by autoclave method. Photoluminescence of CdS and CdSe with particle size of 5–14 nm showed λ_max at 520 nm and 600 nm, respectively, when were excited at 365 nm. These nanoparticles doped into the PVA resulted in the organic/inorganic films (PVA/CdS, CdSe). Photoluminescence, X-ray diffraction and transmission electron microscopy were employed for their characterization.

Cadmium sulfide nanoparticles were synthesized and grown on glass substrates by chemical bath deposition. The method involves the preparation of aqueous solutions containing cadmium chloride (CdCl₂) and thiourea [CS(NH₂)₂] as source materials for cadmium and sulfur components, respectively. Ammonium hydroxide (NH₄OH)–ammonium chloride (NH₄Cl) solution was used as a complexing agent in this study. The hexagonal and cubic crystal structure of as-deposited CdS films, determined by X-ray diffraction (XRD), is shown. The effects of Cd:S ratio variation on the surface morphology and optical properties of CdS films are also reported. The UV-vis transmission spectrum and SEM micrographs indicated that the Cd:S ratio in the aqueous solution had an impact on the band gap as well as the crystallite size and packing density of the CdS particles due to the quantum confinement effect.

Cadmium sulfide nanoparticles have been synthesized by hydrothermal method using cadmium acetate, thiosemicarbazide, and sodium hydroxide as precursors with hexamethylene tetramine as the surfactant. From the X-ray diffraction analysis, it is observed that synthesized CdS nanoparticles show cubic phase. The presence of HMTA in CdS was confirmed by FT-IR analysis. The bandgap value of CdS nanostructure has been estimated by DRS–UV-Visible spectral analysis. The formation of flower-like nanoclusters was observed using scanning electron microscopy (SEM). The application of CdS nanoparticles in photocatalytic degradation was also studied.

Fluorescent semiconductor nanocrystals have been widely used as fluorescent materials in chemical sensors, biotechnology, medical diagnostics, biological imaging and many other fields. Compared to the conventional organic fluorophores, the inorganic quantum dots (QDs) have many advantages, including broad absorption spectra, narrow emission spectra, good photostability and long fluorescent lifetime after excitation. Here, the high quality CdS QDs were synthesized directly from sulfur and CdO using the paraffin liquid as solvent and the oleic acid as the reacting media. The synthesized CdS QDs with a zinc blende (cubic) crystal structure were proved by X-ray diffraction. HRTEM observation revealed that the CdS QDs were uniform and the average grain size was about 4 nm. The optical properties of the CdS QDs were characterized by using photoluminescence (PL) spectrophotometer and Ultraviolet-visible (UV-Vis) absorption spectrophotometer. The formation mechanism of CdS QDs in the paraffin liquid and oleic acid system was proposed.

In the present work, Cadmium sulfide (CdS) and CdS doped with copper (Cu) and iron (Fe) metals thin films were deposited on glass slides using chemical bath deposition technique. 1% content of Cu and Fe were used as dopants. The films were prepared at a reaction temperature of approximately 80^∘C and for an hour as the reaction time without any heat treatment. The pure and doped films were diagnosed and examined by several techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and UV-visible spectrometry to study the effect of the doping and the type of dopant material on the surface, structural and optical properties of CdS films. From the results of XRD can be noticed there is no effect for the dopant on the type of crystal structure except small shifting in the position of main peak after doping. The bandgap energy of the Fe-doped CdS films has been found to be lower than that of the undoped films between 2.62 eV and 2.43 eV.

Two asymmetrical amphiphilic phthalocyanines simultaneously containing hydrophobic alkoxy and hydrophilic 15-crown-5-ether substituents at the phthalocyanine periphery H₂{Pc(15C5)₃[(OC₈H${}_{17}{)}_2$]}(Pc-1) and H₂{Pc(15C5)[(OC₈H${}_{17}{)}_6$]}(Pc-2) and their symmetrical analogue H₂[Pc(OC₈H${}_{17}{)}_8$] (Pc-3) have been synthesized and characterized. The Pc-n/CdS ($n=$ 1, 2 and 3, respectively) hybrid films are obtained successfully via a simple quasi-Langmuir–Shäfer (QLS) method using H₂S-vapor annealing over the Pc-n/Cd${}^{2+}$ self-assembled film formed at the interface of the air/CdCl₂ aqueous solution. The film-structure and properties of both the hybrid Pc-n/CdS and pure Pc-n films are comparatively studied by a wide range of methods including UV-vis, polarized UV-vis, XRD, SEM and I–V measurements. Experimental results exhibit a slipped co-facial stacking mode in an “edge-on” conformation ($H$-type aggregate) formed for the phthalocyanine molecules in both pure Pc-n films and the corresponding Pc-n/CdS hybrid films, with increasing intermolecular $\pi$–$\pi$ interactions in the order of Pc-n <Pc-n/CdS and Pc-3/CdS <Pc-2/CdS <Pc-1/CdS, respectively. Accordingly, film-microstructures, crystallinity and conductivity are effectively improved by introducing CdS nanoparticles into the 15-crown-5-substituented phthalocyanines forming Pc-1/CdS and Pc-2/CdS hybrid films. These render excellent sensing performance towards NO₂ in the 0.05–2.5 ppm range within a fast dynamic exposure period of 30 s. Strikingly, Pc-1/CdS hybrid film presents an unprecedented high sensitivity of 157.3%.ppm${}^{-1}$vs. very low NO₂ concentration range of 0.05˜0.25 ppm, achieving one of the best room temperature sensing performances in terms of high sensitivity, rapid responsibility and low detection limit among self-assembled film-based NO₂ sensors.

II–VI Semiconductor nanocrystals (NCs) with tunable visible emission, such as CdS, CdSe and CdTe, were synthesized in aqueous solution using thiols as capping molecules. Hydrazine was found to promote the growth of NCs through a special mechanism. In only a few hours, the synthesis process was completed at room temperature. Under moderate conditions, the capping molecules not only changed the growth rate of NCs simply by varying the concentration, but also altered the spectral properties of NCs. The capping molecules with amino groups were propitious to the growth of CdS NCs, whereas the kinetic growth of CdS NCs was more affected by the surface passivation efficiency of NCs than by steric hindrance in the system. The fastest growth of the CdS NCs was achieved when glutathione was used as a capping molecule, while the emission of CdS and CdSe NCs were shown to remain steady and tunable using the same capping molecule. The growth rate of 3-mercaptopropionic acid-capped CdS and CdSe NCs slowed down significantly, while CdTe NCs were obtained with excellent emission properties when capped with the same molecule. Furthermore, our approach will also be useful for the study of the kinetic growth of NCs in aqueous solution.

A new-type photocatalyst of cadmium sulfide carbon nanotubes (CdS/CNTs) was prepared by the hydrothermal method. This as-prepared CdS/CNTs composite photocatalyst was proved to exhibit an excellent photocatalytic activity for degradation of tetracycline (TC). Specially, the 95%-CdS–5%-CNTs composite photocatalyst played the best degradation rate (81.2%) in 60 min under the visible light irradiation. Moreover, this 95%-CdS–5%-CNTs composite photocatalyst possessed great stability and could be used at least four cycles with almost no loss of photocatalytic efficiency. Furthermore, the as-synthesized CdS/CNTs composite photocatalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-Vis diffused reflectance spectra (UV-Vis), Raman and thermal gravimetry (TG). In addition, the possible mechanism and kinetics of photodegradation of TC with CdS/CNTs photocatalyst was also discussed.

A unique CdS/Fe₃O₄/rGO composite photocatalyst is successfully synthesized by the microwave method. It displays promising photocatalytic activity towards the photo-degrading of tetracycline (TC) in aqueous solution, the degradation rate of TC is 69% with adding 0.1g CdS/Fe₃O₄/rGO photocatalyst into 20mg/L tetracycline for 2h under visible light irradiation. Furthermore, the mechanism was systematically investigated by active species trapping experiment. It can be known that ${\mathrm{\text{e}}}^{-}\mathrm{\text{was}}$ the major active species in the photodegradation process and the possible process of charge transfer for CdS/Fe₃O₄/rGO was proposed based on the experimental results. The as-prepared samples were carefully evaluated by XRD, TEM, XPS, VSM, PL spectra, Raman spectrometer.

An integrated tandem photoelectrochemical (PEC) cell, composed of a three-dimensional (3D) ZnO/CdS/NiFe layered double hydroxide (LDH) core/shell/hierarchical nanowire arrays (NWAs) photoanode and a $p$-Cu₂O photocathode, was designed for unassisted overall solar water splitting in this study. The optical and photoelectrochemical characteristics of ZnO-based photoanodes and Cu₂O photocathode were investigated. The results show that ZnO/CdS/NiFe LDH nanostructures offer significantly enhanced performances with a photocurrent density reaching 5.8mA$\cdot$cm${}^{-2}$ at 0.9V and an onset potential as early as 0.1V (versus RHE). The enhancement can be attributed to the existence of CdS nanoparticles (NPs) which boosts the light absorption in visible region and enhances charge separation. Moreover, the introduction of NiFe LDH nanoplates, with unique hierarchical mesoporous architecture, promotes electrochemical reactions by providing more active sites as co-catalyst. On the above basis, the ZnO/CdS/NiFe LDH–Cu₂O two-electrode tandem cell system was established. At zero bias, the device shows a photocurrent density of 0.4mA$\cdot$cm${}^{-2}$ along with the corresponding solar-to-hydrogen (STH) conversion efficiency reaching 0.50%. Our results indicate that the tandem PEC cells consisting of metal–oxide–semiconductor photoelectrodes based on Earth-abundant and low-cost materials hold promising application potential for overall solar water splitting.