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Electronic structure calculations have been carried out using Extended Hückel tight-binding method for 2H—MoTe₂ for the cases both unrotated and with rotated planes. It has been found that relative rotations of the tellurium layers ranging from 5 to 16 degrees have the same total energies and total energies/atom as the unrotated structure. Moreover, an increased in metallic behavior has been observed, as long as the degrees of rotated planes are increased. Finally, good agreement has been found among previous experimental measurements in the diffraction pattern of irradiated MoTe₂ and our calculated 5, 6 and 7 degrees of rotations.

Thin films of amorphous selenium (a-Se) have been prepared by thermal evaporation. DC conductivity measurements were carried out on these films in the temperature range between 60 and -50°C. Above room temperature, the dark conductivity is thermally activated as usually observed in chalcogenide semiconductors. At low temperatures, the unexpected increase in the dark currents could be attributed to the phase change in the a-Se film. The current–voltage, I–V, curves showed a phase transition temperature of about 10°C.

We have carried out thermally stimulated current (TSC) measurements on as-grown Tl₂Ga₂S₃Se layered single crystals in the temperature range 10–60 K with different heating rates of 0.6–1.5 K s¹. The data were analyzed by curve fitting, initial rise, and peak shape methods. The results were in good agreement with each other. Experimental evidence was obtained for trapping center in Tl₂Ga₂S₃Se crystal with activation energy of 11 meV. The capture cross section and concentration of the traps were found to be 1.5 × 10^-23cm² and 1.44 × 10¹⁰cm^-3, respectively. Analysis of the TSC data at different light excitation temperatures leads to a value of 18meV/decade for the traps distribution.

The ${\mathrm{\text{Cu}}}_2{\mathrm{\text{ZnSnS}}}_4$, ${\mathrm{\text{Cu}}}_2{\mathrm{\text{ZnSnSe}}}_4$ and ${\mathrm{\text{Cu}}}_2{\mathrm{\text{ZnSnTe}}}_4$ and their alloys have been frequently investigated experimentally owing to their suitable bandgap for the solar cell applications. For the first time, density functional theory is applied to explore the structural, electronic and optical properties of ${\mathrm{\text{Cu}}}_2\mathrm{\text{ZnSn}}({\mathrm{\text{S}}}_{1-x}{\mathrm{\text{Te}}}_x)$ and ${\mathrm{\text{Cu}}}_2\mathrm{\text{ZnSn}}({\mathrm{\text{Se}}}_{1-x}{\mathrm{\text{Te}}}_x)$$(x=0,0.25,0.5,0.75,1)$. The energy minimization procedure reveals that the Kesterite phase is stable compared to the Stannite structure. Lattice constants of the compounds are in good agreement with the previous experimental results. The alloys have direct bandgaps which decrease by increasing the concentration of Te. The chemical bonding among the cations and anion is dominantly covalent. Electronic bandgap dependent optical properties like absorption coefficient and optical conductivity are studied in detail. The materials show strong response in the visible region of energy spectrum indicating the usefulness of these materials for optoelectronic devices.

In this paper, we study the optoelectronic properties of quaternary metal chalcogenide semiconductor ABaMQ₄ (A = Rb, Cs; M = P, V; and Q = S) compounds using state-of-the-art density functional theory (DFT) with TB-mBJ approximation for the treatment of exchange-correlation energy. In particular, the electronic and optical properties of the relaxed geometries of these compounds are investigated. Our first-principles ab-initio calculations show that the CsBaPS₄ and RbBaPS₄ compounds have direct bandgaps whereas the CsBaVS₄ compound exhibits indirect bandgap nature. Importantly, the theoretically calculated values of the bandgaps of the compounds are consistent with experiment. Furthermore, our analysis of the electronic charge densities of these compounds indicates that the above quaternary chalcogenides have mixed covalent and ionic bonding characters. The effective masses of these compounds are also calculated which provide very useful information about the band structure and transport characteristics of the investigated compounds. Similarly, high absorptivity in the visible and ultraviolet regions of the electromagnetic spectrum possibly predicts and indicates the importance of these materials for potential optoelectronic applications in this range.

Solar cells convert electricity from the solar spectrum to more than 60%. Researchers focused on this promising field because of the most demanding renewable source of electrical energy. Based on the demand, we focused our study on bismuth-doped tin chalcogenide materials for the optoelectronic and solar cell applications. The effect of bismuth concentration on structural, electronic, thermodynamic and optical properties of Sn${}_{0.75}$Bi${}_{0.25}$Te and Sn${}_{0.25}$Bi${}_{0.75}$Te materials is studied based on density functional theory (DFT). Generalized gradient approximation (GGA) was proposed to calculate structural parameters, density of states and band structure. Here the lattice parameter increases when increasing bismuth concentration. The parent binary SnTe is in semiconducting behavior with a narrow direct bandgap of 0.234 eV (L-L). From the calculated thermal and optical results, the Gruneisen parameter is maximum for Sn${}_{0.25}$Bi${}_{0.75}$Te and Debye temperature is maximum for Sn${}_{0.75}$Bi${}_{0.25}$Te. The studied materials are consistent in IR, visible and UV regions and they are adorable for IR optical detectors and solar cell applications.

Structural, electronic, magnetic and optical properties of Cu₄Mn₂Te₄ have been reported earlier by the authors, and here, the transport properties of the same are discussed along with the band structure investigation of the neodymium-doped cubic material LMO (LiMn₂O₄), namely LiMn${}_{1.75}$Nd${}_{0.25}$O₄ compound, under spin polarized schemes through the First Principles calculations. The Full Potential-Linearized Augumented Plane Wave Method (FP-LAPW) method is adopted to investigate the electronic structures based on the framework of Density Functional Theory (DFT). Exchange potentials are treated using the Generalized Gradient Approximations (GGA). Cohesive energy calculations reveal that the ferromagnetic phase of LiMn${}_{1.75}$Nd${}_{0.25}$O₄ and the antiferromagnetic phase of Cu₄Mn₂Te₄ exhibits a stable phase. Of these, FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ shows a semi-metallic-like behavior in spin-up channel and metallic behavior in spin-down channel whereas antiferromagnetic Cu₄Mn₂Te₄ exhibits a band gap in both spin-up and spin-down channels. Dirac points are identified at −0.0625eV in the band structure plot of FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ at its high symmetry points $\mathrm{\Gamma }$ and W which is an indication of high electron mobility at ambient condition. The presence of flat and dispersive bands around the Fermi energy level is an indication of high thermopower, and it is present in both the compounds FM-LiMn${}_{1.75}$Nd${}_{0.25}$O₄ and AFM-Cu₄Mn₂Te₄. From the present computations, at 300K, a power factor range of ($S^2\sigma$ scaled by relaxation time in $\mu$W/msK²) $1.75\times 10^{20}\uparrow$ and $9.37\times 10^{21}\downarrow$ is obtained for ferromagnetic LiMn${}_{1.75}$Nd${}_{0.25}$O₄ compounds at up and down spins, respectively. A typical power factor ($\mu$Wm${}^{-1}$s${}^{-1}$K${}^{-2}$) of $4.79\times 10^{15}\uparrow$ and $2.97\times 10^{18}\downarrow$ is obtained for antiferromagnetic Cu₄Mn₂Te₄ at 325K required for good thermoelectric performance.

To gain insight into the electronic properties of MoSe₂ (molybdenum selenide, also known as drysdallite), electronic structure calculations, total and projected density of states, crystal orbital overlap population and Mulliken population analysis were performed. The calculated energy bands depict a semiconductor behavior with a direct gap (at K) of 0.91 eV and an indirect gap (from Γ to K) of 3.6 eV, respectively. Total and projected density of states provided information about the contribution from each orbital of each atom to the total density of states. Moreover, the bonding strength between some atoms within the unit cell was obtained. Mulliken population analysis corroborates the electron filling of the Mo d_z2 orbitals in agreement with another experimental and theoretical results.

The temperature dependence of photoinduced anisotropy in the photoconductivity of As₂Se₃ and Sb₂S₃ thin films was investigated, in the interval between -50 and 70°C. Our results demonstrate that for both As₂Se₃ and Sb₂S₃ thin films, the anisotropy percentage falls with increasing temperature. We surmise that the aligning effect of the linearly polarized light was diluted with increasing temperature, because the latter induces similar mechanisms to those induced by polarized light, but in an isotropic fashion.

The defect centers in TlGaSSe single crystals have been investigated by performing thermoluminescence (TL) measurements with various heating rates between 0.5 K/s and 1.0 K/s in the temperature range of 10–180 K. The TL spectra, with peak maximum temperatures at 39 K and 131 K, revealed the existences of two defect levels. Curve fitting, initial rise and peak shape methods were used to determine the activation energies of two defect centers. The experimental results also showed that the trapping process was dominated by second-order kinetics for the trap related with low temperature peak while the general order (mixed order) kinetics was dominant for the trap donated to high temperature peak. Furthermore, heating rate dependences and traps distributions were studied for two defect centers separately. Thermal quenching effect dominates the behavior of these defects as the heating rate is increased. Also, quasi-continuous distributions were established with the increase of the activation energies from 16 meV to 27 meV and from 97 meV to 146 meV for the traps associated with the peaks observed at low and high temperatures, respectively.

The structural, electronic and optical properties of mercury cadmium sulfide (Hg${}_{1-x}$Cd${}_x$S) alloys with $x$ = 0.0, 0.25, 0.5, 0.75 are studied using density functional theory (DFT) within full-potential linearized augmented plane wave (FPLAPW) method. We used the local density approximation (LDA), the generalized gradient approximation (GGA), Hubbard-corrected functionals (GGA/LDA+$U$) and the modified Becke–Johnson (LDA/GGA)-mjb hybrid potentials to treat the exchange-correlation functional $(E_{ex})$. We found that LDA functional predicts better lattice constants than GGA functional. Mercury sulfide (HgS) binary alloy was found to exhibit a semi-metallic behavior using all functional with an inverted band gap close to the experimental value. However, the hybrid functionals were more successful than LDA and GGA functionals to predict the correct electronic structure of Hg${}_{1-x}$Cd${}_x$S ternary alloys. The results of the electronic and optical band gaps are consistent for Hg${}_{1-x}$Cd${}_x$S ternary alloys.

Infrared (IR) reflectivities are registered in the frequency range of 50–2000 cm${}^{-1}$ for Ag₃In₅Se₉ and Ag₃In₅Te₉ single crystals grown by Bridgman method. Three infrared-active modes are detected in spectra. The optical parameters, real and imaginary parts of the dielectric function, the function of energy losses, refractive index, absorption index and absorption coefficient were calculated from reflectivity experiments. The frequencies of transverse and longitudinal optical modes (TO and LO modes) and oscillator strength were also determined. The bands detected in infrared spectra were tentatively attributed to various vibration types (valence and valence-deformation). The inversion of LO- and TO-mode frequencies of the sandwiched pair was observed for studied crystals.

Near-infrared (NIR) dyes are used in various applications such as organic solar cells and photodynamic therapy sensitizers. One example of a class of dyes, octa-arylthio-substituted phthalocyanines (Pcs), can effectively absorb NIR light above 800 nm. The substitution of the Pc’s peripheral sulfur effectively introduces extra functions without significant perturbation of the optical properties. However, the synthesis of phthalonitrile precursors containing various functionalized arylthio groups has been limited. Herein, we provide the three-component-type coupling reactions for synthesizing phthalonitriles with various functionalized chalcogen-aryl groups. Organometallic reagents were prepared from aryl halides, elemental chalcogen, and 3,6-bis(trifluoromethanesulfonyloxy)phthalonitrile can lead to functionalized phthalonitriles in a one-pot procedure. Commonly used methods were utilized to prepare the corresponding Pcs. This reaction can be extended to other group-16 elements, chemoselective organomagnesium, and organozincate reagents. The NIR absorption and fluorescence properties of Pcs were also revealed and rationalized under substitution effects.

First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and magnetic properties of KX ($\text{X}=\text{S}$, Se and Te) binary alkali–metal chalcogenides compounds. These compounds in different crystalline phases, NaCl (B1), CsCl (B2), ZB (B3), NiAs (B8${}_1)$, WZ (B4) and Pnma, were calculated within the generalized gradient approximation (GGA-PBE) and the modified Becke–Johnson approach (mBJ-GGA-PBE) for the exchange–correlation energy and potential. We found that the most stable phase for the KX binary compounds is the nonmagnetic Pnma phase. The calculated lattice parameters, bulk moduli, their first-pressure derivatives and internal parameters are in good agreement with the other theoretical data. The electronic band structure and density of states show that half-metallic and magnetic character arises, which can be attributed to the presence of spin-polarized $p$ orbitals in the group VI elements. KX ($\text{X}=\text{S}$, Se and Te) compounds, except for KSe and KTe in the CsCl and NiAs phases, show HM character in all phases, with an integer magnetic moment of 1${\mu }_{\mathrm{\text{B}}}$ per formula unit and HM gaps.

The pressure and temperature dependent elastic properties of mercury chalcogenides (HgX; X = S, Se and Te) with pressure induced structural transition from ZnS-type (B3) to NaCl-type (B1) structure have been analyzed within the framework of a model interionic interaction potential with long-range Coulomb and charge transfer interactions, short-range overlap repulsion and van der Waals (vdW) interactions as well as zero point energy effects. Emphasis is on the evaluation of the Bulk modulus with pressure and temperature dependency to yield the Poisson's ratio ν, the Pugh ratio ϕ, anisotropy parameter, Shear and Young's modulus, Lamé's constant, Klein man parameter, elastic wave velocity and Debye temperature. The Poisson's ratio behavior infers that HgX are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations.

First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic and magnetic properties of NaS, NaSe and NaTe alkali-metal chalcogenides binary compounds. These compounds in different crystalline phases: NaCl (B1), CsCl (B2), ZB (B3), NiAs (B8₁), WZ (B4) and Pnma were calculated within the generalized gradient approximation (GGA-PBE) and the modified Becke–Johnson approach (mBJ-GGA-PBE) for the exchange-correlation energy and potential. We found that the most stable phase for the NaX binary compounds is the nonmagnetic Pnma phase. The calculated lattice parameters, bulk moduli, their first-pressure derivatives and internal parameters are in good agreement with the other theoretical data. The electronic band structure and density of states show that half-metallic and magnetic character arises, which can be attributed to the presence of spin-polarized $p$ orbitals in the group VI elements. The NaS, NaSe and NaTe binary compounds show half-metallic character in ZB and WZ phases, with an integer magnetic moment of 1 ${\mu }_{\mathrm{\text{B}}}$ per formula unit and half-metallic gaps.