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The effect of 2MeV energy electrons with fluences from $0.5\times 10^{17}$ to $4.0\times 10^{17}$ electron/cm² on the crystal structure, surface morphology, absorption spectrum, band gap, Raman spectrum and microhardness of ZnS crystal was investigated. The crystal structure of ZnS is face-centered cubic with space group F-43m. Upon irradiation with a fluence of $4\times 10^{17}$ electron/cm², the unit cell parameter decreased by 0.0195Å, and the coordinates of the Zn${}^{+2}$ ions were changed. Irradiation with fluences ranging from $0.5\times 10^{17}$ to $4\times 10^{17}$ electron/cm² increased crystallite size from 20nm to 28nm. The study of the surface morphology of the ZnS single-crystal revealed that irradiation caused a reduction in both the width ($R_a$) and height ($R_z$) of the surface roughness. The band gap of the ZnS single-crystal decreased from 3.521 to 3.506eV when irradiated with fluence electrons from $0.5\times 10^{17}$ to $2.5\times 10^{17}$electron/cm². Raman spectrum observations showed an increase in the longitudinal optical (LO) mode peak (350cm${}^{-1}$) intensity following the irradiation of ZnS single-crystal with electrons. The microhardness of the ZnS single-crystal showed an exponential increase by 20% when irradiated with fluences from $0.5\times 10^{17}$ to $2.5\times 10^{17}$electron/cm².

Within a tight-binding Su–Schrieffer–Heeger model, the elementary excitations and optical absorption of a polyacene chain are investigated. The polyacene chain composed of a number of aromatic rings is considered as two strongly coupled polyacetylene chains with an open boundary condition. First of all we found an interchain-coupled neutral soliton in a pristine chain as a consequence of odd-number sites in each chain. There are two localized electronic states accompanying the soliton and appearing in the conduction and valence bands, respectively. Moreover, an injected electron or hole will induce a polaron-like deformation mixed with the interchain soliton, while two extra electrons or holes will result in three separate solitons, among which one is doubly charged and other two are neutral. The optical absorption due to these elementary excitations are obtained.

We derive a simplified Bethe–Salpeter equation for calculating optical absorption based on the assumption of a local electron–hole interaction. The original four-point equation for the kernel is reduced to a two-point one. A connection to the exchange–correlation kernel in time-dependent density functional theory can be established. The resulting f_xc is found to be -W/2 where W contains only the short-range (local) part of the Coulomb screened interaction. This simple approximation was successfully applied to optical absorption spectra of some excitonic crystals, reproducing not only the continuum excitons but also the bound ones.

The intersubband optical absorption in cylindrical quantum dot quantum well (QDQW) for different sizes of QDQW is theoretically studied. The analytical expression of the absorption coefficient is derived by using the compact density-matrix approach and the iterative method. And the numerical calculations are presented for a typical GaAs/AlGaAs QDQW. The results obtained show that the optical absorption coefficient in the QDQW can be importantly modified by size of shell well. Moreover, they also show that the optical absorption is strongly dependent on the incident optical intensity.

The effect of doping with boron, carbon and nitrogen on crystal lattice parameters, electronic band structure and optical absorption of anatase has been studied by means of an ab initio density functional theory approach. The investigations included optimization of crystal structure based on the pseudo-potential plane-wave approach. The spin-polarized calculations of the band structure with the account of on-site Coulomb correlations (LSDA+U) employing the tight-binding linear muffin-tin orbitals method (TB-LMTO) have also been performed. The evaluations of optical absorption were based on the calculations of dielectric function with local field effects taken into account. We find that the crystal lattice relaxation around the doping atoms produces noticeable changes in the band structure, magnetic state and optical properties of the doped compounds. The most considerable effects are the collapse of magnetic moment on carbon atom and an essential reduction of the optical absorption in the region of the impurity band — impurity band transitions. Comparing optical absorption for different kinds of doping and taking into account the intensity distribution of the solar light we come to the conclusion than the doping with boron is the most promising kind of doping for photocatalytic applications of the doped anatase.

Polymer composites in various forms and configuration are being developed in an effort to provide lighter weight construction, better optical and thermal properties to maintain adequate strength and stability. To this end thin film polymer (PMMA) nanocomposites synthesized for purpose of influencing optical luminescence using CdS nanocrystals as filler without incurring losses in mechanical properties, were examined to determine elastic modulus and degree of dispersion. Optical absorption spectroscopy has been used for finding discrete energy levels in CdS/polymer.

By using reactive magnetron sputtering system, titanium dioxide thin films were fabricated onto quartz substrate, and then modified by Ge and Si atoms that were introduced with ion implantation method. XRD, AFM, XPS, and UV-vis were used to characterize these films, and X-ray photoelectron spectroscopy (XPS) was adopted to examine the atomic chemical states of implanted titanium dioxide thin films. The results show that there are Ge and silicon oxides precipitations in TiO₂ matrices. The implanted Ge + Si thin film exhibits an intense absorption band within visible region, which will further benefit its practical applications.

We demonstrate theoretically that terahertz (THz) fundamental band-gap between the electron mini-band in the InAs layer and the heavy-hole mini-band in the GaSb layer can be realized in InAs/GaSb-based type II superlattices (SLs). The THz band-gap can be tuned by varying the widths of the InAs/GaSb layers. The presence of such band-gap can result in a strong cut-off on optical absorption at THz frequencies. For typical sample structures, the THz cut-off of the optical absorption depends sensitively on temperature and a sharper cut-off can be observed at relatively high temperatures. This study is pertinent to the application of InAs/GaSb type II SLs as THz photodetectors.

The interband transition onset frequency of nanoaluminum is found to approximately, linearly decrease as reducing aluminum diameter in the 25–100 nm range. This linear relation is indicated to originate mostly from increased inner strain of nanoparticle caused by the small size effect. This relation realizes to introduce the size dependence of interband transitions into the metallic dielectric function and has its important application in the laser ignition of nanoenergetic materials.

A microscopic theory of dielectric properties of thin molecular films, i.e., quasi 2D systems bounded by two surfaces parallel to XY planes was formulated. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green's functions. It has been shown that two types of excitations can occur: bulk and surface exciton states. Analysis of the optical properties of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. Conditions for the appearance of localized or unoccupied exciton states have been especially analyzed.

A typical nitrogen doped spherical SiC nanocrystal with a diameter of 1.2 nm (Si₄₃C₄₄H₇₆) using linear combination atomic orbital (LCAO) in combination with pseudopotential density functional calculation have been studied. Our selected SiC nanocrystal has been modeled taking all the cubic bulk SiC atoms contained within a sphere of a given radius and terminating the surface dangling bonds with hydrogen atoms. We have examined nine possible situations in which nitrogen has a high probability for replacement in the lattice or placed between atoms in the nanocrystal. We have found that the silicone can substitute with a nitrogen atom in each layer as the constructed nanocrystals remain thermodynamically stable. Also the nitrogen atom can be placed between the free atomic spaces as the more thermodynamically stable position of the nitrogen is between the topmost layers. Also the optical absorption and refractive index energy dispersions of the pure and various stable doped SiC nanocrystals were studied.

The optical properties of alkaline earth borate glasses doped with rare earth are attractive field of research due to many optical applications. We have concentrated on the physical and optical properties of MgO–SO₄–B₂O₃ glass with different concentrations of Dy${}^{3+}$ ions. The samples of glass were prepared using the melting quenching technique. The physical parameter and optical properties of the prepared glass were determined. It was observed that the density of the glass samples increased and the molar volume reduced with respect to Dy${}^{3+}$ ions content. Dy${}^{3+}$: MgO–SO₄–B₂O₃ glass displayed 10 absorption bands with hypersensitive transition around 1265 nm (⁶H${}_{15/6}{\to }^6$F${}_{11/2}$). Two intense luminescence emissions were observed at 482 nm (⁴F${}_{9/2}{\to }^6$H${}_{15/2}$: blue) and 573 nm (⁴F${}_{9/2}{\to }^6$H${}_{13/2}$: yellow) and weak band at 662 nm (⁴F${}_{9/2}{\to }^6$H${}_{11/2}$: red) with excitation wavelength 380 nm. A strong enhancement in the emission peaks at 573 nm in the yellow region was observed with the 0.07 mol% concentration of dysprosium oxide, which may assign to the energy transfer from Mg${}^{2+}$ to Mg${}^{3+}$ ions. Beyond the optimum concentration, contrary result was observed.

In this paper, the effect of incident light intensity, relaxation time, core radius and shell thickness on linear, nonlinear, total optical absorption coefficients and refractive index changes in $GaN/A{l}_{0.1}G{a}_{0.9}N$ core–shell nanowire are theoretically investigated. The presented nanostructure is a cylindrical quantum wire including a shell around the cylinder core. By numerical solution of Schrödinger equation in the cylindrical coordinates with effective mass approximation, the optical absorption coefficients are calculated. The results show that the magnitude of optical absorption coefficients can be adjusted by varying the relaxation time. The positions of resonant peaks of optical absorption coefficients are redshifted by increase of core radius due to decrease of the energy difference between two energy levels. With increase of shell thickness initially, the resonance wavelength of absorption coefficient increases (redshift) and magnitude of absorption coefficient decreases. Then with more increases of the shell thickness, redshifting of resonance wavelength is stopped and magnitude of absorption coefficient is increased. There is a significant increase in the refractive index change with increase of relaxation time.

An investigation of the effect of charges of impurity on the optical properties of a hydrogenic impurity in a disk parabolic quantum dot under magnetic field has been performed by using the matrix diagonalization method. The ground state energy level becomes lower as the charges of impurity increase. The optical absorption coefficient strongly reduces with increasing charges of impurity and is strongly affected by the confinement strength, the magnetic field strength, and density of electron.

Electric field influences on the electronic states and the optical absorption in an asymmetrical quantum well with semiparabolic potential are investigated. The formula for the absorption coefficients in this asymmetrical quantum well with electric field are deduced by applying iterative method and density-matrix approach. The results are discussed with GaAs/AlGaAs materials and show that the external electric field has a significant effect on the electronic states and absorption coefficients of asymmetric quantum wells.

In this paper, the effects of the electric and magnetic fields on the optical absorption of GaAs/AlGaAs quantum multirings were studied. Using the two-dimensional finite element method, energy eigenvalues and wavefunctions were calculated, and optical absorption was obtained by the density matrix approach. The result showed that optical absorption increases with increasing number and size of the rings.

A mathematical expression for the coefficient of optical absorption in amorphous GaAs referred to the far-infrared range is obtained by neglecting the spectrum contribution corresponding to structural disorder. In addition, our results are compared with experimental data and several aspects related to the electronic density of states are discussed.

Direct optical absorption of light in cylindrical quantum dot was theoretically investigated. Analytical expressions for light absorption coefficients were found for two regimes of size quantization: strong and weak. The corresponding selection rules for optical transitions are defined. The expressions for absorption threshold frequencies are found. The obtained results are compared with the case of light direct optical absorption in spherical quantum dot.

Optical absorption of amorphous cadmium oxide in the visible region is investigated by considering the band-gap shift experienced by this material. At the same time, influence of oxygen partial pressure is studied so that new results related to absorption in the visible margin are obtained; these results agree well with experimental data. In addition, phonon density of states and its shift due to the band-gap shift are evaluated.

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of VO²⁺ ions in different alkali lead borotellurite glasses have been studied. The spin-Hamiltonian parameters (g and A), bonding parameter and Fermi contact interaction parameter k have been calculated. The values of spin-Hamiltonian parameters confirm that the vanadyl ions are present in the glasses as VO²⁺ molecular ions in an octahedral site with a tetragonal compression. The number of spins (N) participating in resonance is calculated as a function of temperature (123–393 K) for 9 mol% of VO²⁺ ions in lithium lead borotellurite glass sample. It is observed that N obeys the Boltzmann law. From EPR data, the paramagnetic susceptibility (χ) is calculated at various temperatures and the Curie constant has been evaluated from 1/χ–T graph. The optical absorption spectrum exhibits two bands characteristic of VO²⁺ ions in tetragonal symmetry. The band gap (E_opt) and the Urbach energies (ΔE) have been determined from the ultraviolet absorption edges and are found to be dependant on the size of the alkali ion. The theoretical values of optical basicity (Λ_th) of these glasses have also been evaluated.