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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.