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White light-absorbing materials are in high demand for catalysis and energy harvesting. Due to the UV (ultraviolet) light absorption capacity of graphene and zinc oxide (ZnO) nanoparticles, the light harvesting of the whole range of visible and near-IR (infra-red) light by utilizing these materials is a significant barrier. In this study, a graphene-ZnO nanoparticle composite was prepared from graphene and ZnO powder through a simple and novel hot solvent process at low temperatures without a catalyst or expensive instrumentation. The fabricated composite was found to absorb light efficiently at an extended range of wavelengths (400–1665nm) with strong absorption intensity. Notably, the in situ graphene-ZnO showed a considerably low intensity of absorption in the visible to the near-IR range; however, when the graphene and ZnO powder were combined as a graphene-ZnO composite by ex situ hot solvent synthesis process, the light absorption intensity significantly increased within the whole range. The observation in this study is the first one that indicates that the ex situ hot solvent process tunes the light absorption properties at the extreme level of the visible- to the near-IR range. The prepared composite also showed excellent electrical conductivity. The graphene powder was also prepared through a straightforward self-developed solvothermal process with the help of the exfoliating agent.

The high-pressure behavior of perovskite (MgSiO₃) is studied based on density functional simulations within generalized gradient approximation (GGA). All calculations are performed by using the linear augmented plane waves plus local orbital (LAPW+lo) method to solve the scalar-relativistic Kohn-Sham equations. The static calculations predict a perovskite (pnma phase) — post-perovskite (Cmcm phase) transition occurring at 86 gigapascals (GPa). The similar bulk modulus values, differing only 3 GPa, are given by using three kinds of equation of states. The electronic structure and optical properties of MgSiO₃ at phase transition pressure are also discussed.

Within the framework of the effective-mass approximation, the donor bound exciton states and interband optical transitions in InGaN/GaN strained quantum dot (QD) nanowire heterostructures (NWHETs) are investigated using a variational method, in which the built-in electric field (BEF) effect due to the spontaneous and piezoelectric polarizations and the three-dimensional (3D) confinement of the electron and hole in the QD are considered. Our results show that the position of the ionized donor, the strong BEF, the In-composition and the QD structural parameters have a significant influence on the donor bound exciton binding energy, the electron interband optical transitions and the exciton oscillator strength. The donor bound exciton binding energy increases obviously if the donor position changes from the left-interface to the right-interface. The BEF reduces the bound exciton binding energy and the exciton oscillator strength. The donor bound exciton binding energy increases, if the In-fraction increases. The emission wavelength monotonically increases if the QD height and radius increase.

The absorption edge shifted to long wavelength direction and short wavelength direction of two opposite experimental conclusions have been reported, when the band-gap and absorption spectra of Nb-doped anatase TiO₂ were studied. In order to solve this contradiction, the electronic structure and the optical property of Nb heavy doped anatase TiO₂ have been studied by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with +U method modification. The calculated results indicate that the higher the Nb-doping is, the higher the total energy is, the worse the stability is, the higher the formation energy is, the more difficult the doping is, the wider the optical band-gap is, the more obvious the absorption edge shifting to short wavelength direction is, the lower the absorptivity and the reflectivity is, which is in agreement with the experimental results. The reasonable interpretation of the contradiction has been reported in this paper, too.

Currently, the stability and visible light properties of Ga-2N co-doped ZnO systems have been studied extensively by experimental analysis and theoretical calculations. However, previous theoretical calculations arbitrarily assigned Ga- and 2N-doped sites in ZnO. In addition, the most stable and possible doping orientations of doped systems have not been fully and systematically considered. Therefore, in this paper, the electron structure and absorption spectra of the unit cells of doped and pure systems were calculated by first-principles plane-wave ultrasoft pseudopotential with the GGA$+$U method. Calculations were performed for pure ZnO, Ga-2N supercells heavily co-doped with Zn${}_{1-x}$Ga${}_x$O${}_{1-y}$N${}_y$ ($x=0.03125-0.0625$, $y=0.0625-0.125$) under different co-doping orientations and conditions, and the Zn${}_{16}$GaN₂O${}_{14}$ interstitial model. The results indicated that under different orientations and constant Ga-2N co-doping concentrations, the systems co-doped with Ga-N atoms vertically oriented to the $c$-axis and with another N atom located in the nearest-neighboring site exhibited higher stability over the others, thus lowering formation energy and facilitating doping. Moreover, Ga-interstitial- and 2N-co-doped ZnO systems easily formed chemical compounds. Increasing co-doping concentration while the co-doping method remained constant decreased doped system volume and lowered formation energies. Meantime, co-doped systems were more stable and doping was facilitated. The bandgap was also narrower and red shifting of the absorption spectrum was more significant. These results agreed with previously reported experimental results. In addition, the absorption spectra of Ga-interstitial- and 2N-co-doped ZnO both blue shifted in the UV region compared with that of the pure ZnO system.

First-principles study of elastic, electronic and optical properties of full-Heusler Co₂V(Al, Ge, Ga and Si) compounds are calculated through density functional theory (DFT) to obtain and compare the mentioned properties. Equilibrium lattice constants of these compounds are in good agreement with other works. Electronic calculations are shown full spin polarization at Fermi level for all compounds, so in the down spin, indirect bandgap is calculated as 0.33, 0.6, 0.2 and 0.8 eV for Co₂V(Al, Ge, Ga and Si), respectively. The integer amounts of the magnetic moments are compatible with Slater–Pauling role. The optical treatment of Co₂VGa is different from three other compounds. All mentioned compounds have metallic behavior by 22 eV plasmonic frequency. The imaginary part of the dielectric function for the up spin indicates that the main optical transitions occurred in this spin mode. Moreover, the elastic results show that the Co₂VGa does not have elastic stability, but the other three compounds have fully elastic stability and the Co₂V(Al, Ge and Si) belong to the hardness of materials.

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + $U$ at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of $sp$–$d$. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

The structural, electronic, optical properties and band offsets of Co₂VGa/GaAs(001) interfaces are discussed within the framework of density functional theory (DFT) using the FP-LAPW method, and the exchange-correlation potential is approximated by GGA. All interface structures are stable in the energy point of view, however the V–Ga/As case is found to be more stable than the others. A remarkable potential difference ($\mathrm{\Delta }$V) appeared in all the interfaces, so the Co₂VGa/GaAs(001) interfaces are good candidates for electron injection. In all the cases, there is no full spin polarization at the Fermi level, but high CBO and ${\mathrm{\Phi }}_p$ coefficients make them promising candidates for spin injection in the transport devices. Optical studies confirm the high metallic treatment of these interfaces as the main electron transitions had occurred in the infrared and visible regions. The real parts of the dielectric function in the x-direction indicate the different behaviors of “Co–Co/As and V–Ga/Ga” and “Co–Co/Ga and V–Ga/As” in the infrared area. In addition, the plasmon frequencies had occurred at high UV energies.

First principles and quasi-harmonic Debye model have been used to study the thermodynamic properties, enthalpies, electronic and optical properties of MgO up to the core–mantle boundary (CMB) condition (137 GPa and 3700 K). Thermodynamic properties calculation includes thermal expansion coefficient and capacity, which have been studied up to the CMB pressure (137 GPa) and temperature (3700 K) by the Debye model with generalized gradient approximation (GGA) and local-density approximation (LDA). First principles with hybrid functional method (PBE0) has been used to calculate the electronic and optical properties under pressure up to 137 GPa and 0 K. Our results show the Debye model with LDA and first principles with PBE0 can provide accurate thermodynamic properties, enthalpies, electronic and optical properties. Calculated enthalpies show that MgO keep NaCl (B1) structure up to 137 GPa. And MgO is a direct bandgap insulator with a 7.23 eV calculated bandgap. The bandgap increased with increasing pressure, which will induce a blue shift of optical properties. We also calculated the density of states (DOS) and discussed the relation between DOS and band, optical properties. Equations were used to fit the relations between pressure and bandgaps, absorption coefficient ($\alpha$($\omega$)) of MgO. The equations can be used to evaluate pressure after careful calibration. Our calculations can not only be used to identify some geological processes, but also offer a reference to the applications of MgO in the future.

Half-metallic, optical and thermodynamic phase diagrams of two-dimensional Mn₂ZrZ (Z = Ge, Si) have been calculated by density functional theory (DFT) framework with full-potential linear augmented plane-wave (FP-LAPW) method. The spin-polarized electronic computations show that these layers have metallic behavior with a spin polarization less than 100%. It is observed that with increasing thickness of the layers, both the thermodynamic and energy stabilities increased, and the graphene-like layers of Mn₂ZrGe with a thickness of 7.6955 Å and Mn₂ZrSi with a thickness of 7.551 Å are completely stable thermodynamically. The optical responses of Mn₂ZrZ (Z = Ge, Si) have anisotropy at infrared region versus the optical direction and have high metallic nature in this optical range. The plasmonic frequencies have occurred after the visible edge and the refraction index becomes lower than one after the ultra-violet edge.

The optical properties of an exciton trapped by an ionized donor in an ellipsoidal quantum dot (QD) with both oblate and prolate shapes under applied electric field and hydrostatic pressure have been studied. We have calculated the linear and third-order nonlinear absorption coefficients (ACs) and refractive index changes (RICs) by using a variational method within the perturbation theory. The results show that the QD shape and size have a significant influence on the positions and magnitudes of the peaks of the (ACs) and RICs, moreover, the influence of hydrostatic pressure and electric field under different QD shape is also different.

We have grown orthorhombic barium disilicide (${\mathrm{\text{BaSi}}}_2$) thin-films on modified silicon (Si) substrates by a thermal evaporation method. The surface modification of Si substrate was performed by a metal-assisted chemical etching method. The effects of etching time $t_e$ on crystalline quality as well as optical and electrical properties of the ${\mathrm{\text{BaSi}}}_2$ films were investigated. The obtained results showed that substrate modification can enhance the crystalline quality and electrical properties; reduce the light reflection; and increase the absorption of the ${\mathrm{\text{BaSi}}}_2$ thin-films. The $t_e$ of 8 s was chosen as the optimized condition for surface modification of Si substrate. The achieved inferred short-circuit current density, Hall mobility, and minority carrier lifetime of the ${\mathrm{\text{BaSi}}}_2$ film at $t_e$ of 8 s were $38{\mathrm{\text{mA/cm}}}^2$, $273{\mathrm{\text{cm}}}^2/\mathrm{\text{Vs}}$, and $2.3\mu$s, respectively. These results confirm that the ${\mathrm{\text{BaSi}}}_2$ thin-film evaporated on the modified Si substrate is a promising absorber for thin-film solar cell applications.

The optical and electronic properties of pure graphene, nitrogen doped graphene, gallium doped graphene and nitrogen and gallium co-doped graphene were researched based on the first-principle method of density functional theory (DFT). Pure graphene has a zero-band structure, and when doped in graphene, its bands are opened. In this study, the bandgap of N-doped graphene was 0.20 eV, Ga-doped graphene was 0.35 eV and N–Ga co-doped graphene was 0.49 eV. They also have different electron density. In the N–Ga co-doped graphene, the N atom gained more electrons (−0.6 1e) than the N-doped graphene (−0.27 e), and the Ga atom lost more electrons (1.80 e) than the Ga-doped graphene (1.75 e). Moreover, the optical properties of pure graphene and doped graphene were analyzed and compared. These properties include complex refractive index, dielectric function and light absorption. From these analysis results, it can be seen that the doping study in graphene has effectively improved the optical and electrical properties of graphene. This study provides an effective theoretical foundation for the future development of graphene-based photoelectric devices.

The unique optical properties of SiGeSn alloy contribute to its remarkable potential in Si photonics applications. In this paper, the first-principles plane-wave super-soft pseudo-potential generalized gradient approximation $+U$$(\mathrm{\text{GGA}}+U)$ method was used to investigate the 96-atom supercell structure of Si${}_x$Ge${}_{96-x-y}$Sn${}_y$ ($0\le x=y\le 9$) alloy. The lattice constants, electronic structure, mechanical properties and optical properties of the alloy were discussed. Results show that the lattice constant increases, the bandgap width decreases, resist external forces is weakened, and the bulk is easily deformed of Si${}_x$Ge${}_{96-x-y}$Sn${}_y$ alloy with the increase in silicon-tin content. The dielectric function, refractive index, and photoconductivity of Si${}_x$Ge${}_{96-x-y}$Sn${}_y$ alloy vary with the concentration of silicon and tin. The increase in silicon-tin concentration leads to an increase in infrared (IR) light absorption, resulting in a red shift. The effective mass of the electron decreases, the effective mass of the hole increases in the alloy, and the ratio $D$ gradually increases, indicating that the carrier life is prolonged with the increase in Si and Sn concentrations.

In this paper, we formed two graphene/C₂P₄ van der Waals (vdW) heterostructures (HSs) by stacking the graphene and the C₂P₄ monolayer which have been predicted by us. First, we investigated the stability of C₂P₄ monolayer, and calculated the binding energies and flat average differential charge density of two vdW-HSs. Second, we found that two graphene/C₂P₄ vdW-HSs are all direct semiconductors with bandgap as 0.051/0.064eV and 0.536/0.697eV under GGA-PBE/HSE06 functional, respectively, which provides a way to unfold the zero bandgap of graphene or let an indirect monolayer to be a relevant direct semiconductor. Additionally, two graphene/C₂P₄ vdW-HSs possess high absorption coefficients (16%∼18%) for the visible light and higher absorption coefficients (22%) for the near ultraviolet light, respectively. These admirable properties make two vdW-HSs as novel and potential two-dimensional materials applied on optoelectronic, electronic and photovoltaics devices.

Based on the density functional theory (DFT) calculations, the structural, electronic, optical and thermoelectric properties of the MnFeTe Heuslerene compound have been investigated. The total energy change curve in terms of volume refers to the ground state point and equilibrium volume. By applying mBJ approximation, this compound has perfect half-metallic behavior of 100% spin polarization at the Fermi level with 7${}_{\mu B}$ magnetic moment. Optical calculations show that the semiconductor behavior with an optical absorption gap occurred by incident light perpendicular to the MnFeTe Heuslerene plane. The figure of merit coefficient (ZT) has reached 3.5 at 50K temperature, which makes it an excellent candidate for thermoelectric applications. Also, the power factor (PF) of this compound has reached its maximum value at room temperature.

Using the full-potential linearized augmented plane-wave method (FP-LAPW), we have performed a detailed theoretical investigation on the pressure-induced phase transitions in KNbO₃. Results obtained show that the pressure will induce a series of phase transitions from rhombohedral to orthorhombic, to tetragonal and finally to the cubic phase, with transition pressures being 8, 15 and 24 GPa, respectively. By analyzing the internal atomic coordinates, we found with increasing pressure, the oxygen octahedron would distort, and the orthorhombic and tetragonal phases would tend to make transitions to the tetragonal and cubic phase, respectively. We also calculated the optical properties of KNbO₃, and found that the dielectric function spectra ∊(ω) of different phases were similar to each other, and the effect of pressure on ∊(ω) spectra were small. However, the second harmonic generation (SHG) coefficients in different phases were greatly different.

First principles studies of structural, elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite under pressure are reported using the pseudopotential plane wave method within the local density approximation (LDA). The calculated equilibrium lattice is in good agreement with the available experimental data. The elastic constants and their pressure dependence are calculated using the static finite strain technique. A linear pressure dependence of the elastic stiffnesses is found. Band structures show that tetragonal CaSiO₃ perovskite is a direct band gap material. In order to understand the optical properties of tetragonal CaSiO₃ perovskite, the dielectric function, absorption coefficient, optical reflectivity, refractive index, extinction coefficient, and electron energy loss are calculated for radiation up to 40 eV. This is the first quantitative theoretical prediction of the elastic, electronic and optical properties of tetragonal CaSiO₃ perovskite, and it still awaits experimental confirmation.

Transparent conductive oxide is a thin film to be used in numerous applications throughout the industry in general. Transparent electrode materials used in these industries are in need of light transmittance with excellent high and low electrical characteristics, substances showing the most excellent physical properties while satisfying all the characteristics such as indium tin oxide film. However, reserves of indium are very small, there is an environmental pollution problem. So the study of zinc oxide (ZnO) is actively carried out in an alternative material. This study analyzed the characteristics by using a direct current (DC) magnetron sputtering system. The electric and optical properties of these films were studied by Hall measurement and optical spectroscopy, respectively. When the Al target input current is 2 mA and 4 mA, it demonstrates about 80% transmittance in the range of the visible spectrum. Also, when Al target input current was 6 mA, sheet resistance was the smallest on PET substrate. The minimum resistivity is 3.96×10^-3 ohm/sq.

First-principles calculations based on density functional theory (DFT) were used to investigate the mechanical properties, elastic anisotropy, electronic structure, optical properties and thermodynamic properties of a new quaternary MAX phase (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ and its counterpart W${}_3$AlC${}_2$ under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ is faster than that of axial shrinkage under hydrostatic pressure. The stress–strain method and Voigt–Reuss–Hill approximation were used to calculate elastic constants and moduli, respectively. These compounds are mechanically stable under hydrostatic pressure. Moreover, the moduli of (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ and W${}_3$AlC${}_2$ increase with an increase in pressure. The anisotropic indexes and surface constructions of bulk and Young’s moduli were used to illustrate the mechanical anisotropy under hydrostatic pressure. Electronic structure and optical property of (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ and W${}_3$AlC${}_2$ have also been discussed. The results of Debye temperature reveal that the covalent bonds among atoms in (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ may be stronger than that of W₃AlC${}_2$. The heat capacity, $C_p$–$C_v$, and thermal expansion coefficient of (W${}_{2/3}$Ti${}_{1/3}$)${}_3$AlC${}_2$ and W${}_3$AlC${}_2$ were discussed in the ranges of 0–30 GPa and 0–2000 K using quasi-harmonic Debye model considering the phonon effects.