جستجوی مقالات مرتبط با کلیدواژه « خواص نوری » در نشریات گروه « شیمی »

In the current research, the calculations were mainly done using Quantum-Espresso computing package and pseudo-potential method in the framework of density functional theory and local density approximation (LDA). In addition, random phase approximation has been used in the investigation of optical properties. The large negative values of the real part of the dielectric function, show that the materials exhibit a behavior similar to that of Drude-like. Where the value of is negative or very close to zero, the electromagnetic wave does not propagate and absorption and dissipation processes take place. The diagrams of the imaginary part of the dielectric function indicate that the absorption process started from small energies and yttrium carbide MXenes (Yn+1Cn; n=1, 2, 3) have no energy gap, which confirms the metallic nature. Also the most obvious peaks in the y-direction indicate the greater interaction of electrons and photons in this direction. The inverse ratio of the real part of the dielectric function and the reflection spectrum shows that where the real part of the dielectric function is negative, the reflection spectrum has the highest value for Y2C, Y3C2, and Y4C3 compounds. These peaks approach zero in the photon energy range of 6-7 eV.

In this study, nanostructured SnS thin films were prepared using two complexing agents of ammonium acetate and hexamethylenetetramine (HMTA) by chemical bath deposition method on the glass andpolyethylene terephthalate (PET) substrate. The effect of complexing agents on surface morphology, structure, optical properties and particle size of the films were investigated by various techniques. The FE-SEM images of the samples showed that the SnS nanoparticles were coated as dense and homogenous on the substrate. The XRD results indicated that the SnS thin films well-crystallized and had orthorhombic crystal structure. The energy gap values of the films varied from 1.06 to 1.07 eV. The results of ultraviolet-visible spectrum of the samples showed that the SnS films had low transmittance values in the visible region, therefore they can be used as an absorber layer in the solar cells.

In this study, ZnO/TiO_2 : Ag composite fibers were prepared by a simple stretching method. The prepared fiber nanocomposites' structural, optical and photocatalytic properties were investigated. X-ray diffraction (XRD) results showed that the structure was successfully synthesized. Scanning electron microscopy (SEM) images showed that the diameter of the prepared fibers was about 10 micrometers. Fourier transform infrared (FTIR) spectroscopy and EDX energy scattering confirmed the strong bonds of the relevant elements and their presence in the composite structure. Increasing the calcination temperature improved the structure and purity of the composite. The photocatalytic performance of nanofiber composites for the degradation color of methylene blue (MB) under UVA light was studied. It was observed that the prepared nanofibers have suitable physical-optical properties and photocatalyst properties (98%) under UVA light exposure in 100 min for the treatment of industrial wastewater containing dyes.

In this study, PbWO4 nanopowders were prepared by a simple and cost-effective co-precipitation method. The prepared nanoparticles' structural, optical, scintillation, photocatalyst, and antibacterial properties were investigated. X-ray diffraction (XRD) showed that the structure was successfully synthesized and assigned to the Scheelite phase with the tetragonal structure of PbWO4. The scanning electron microscope (SEM) images showed that the prepared particle's size is ~80 nm. Fourier Transform Infrared Spectroscopy (FTIR) and Energy Dispersion X-Ray (EDX) confirmed the strong bonds of related elements and the presence of Pb, W, and O elements in the structure. Luminescence studies under ion beam and ultraviolet radiation showed that the prepared nanoparticles have strong blue-green scintillation sensitivity at room temperature. The photocatalytic performance was studied using the degradation of methylene blue (MB) dye under UVA light irradiation. It was observed that the prepared nanopowder has 95.6% decolorization properties in 60 minutes under light irradiation. The physical and scintillation characteristics obtained from the synthesized nanopowders show that these nanomaterials can be used in optical applications, industrial wastewater treatment, and ionizing radiation detectors.

In this paper, the optical properties of nanosheet and (6,6) armchair As2GeSe nanotube (the real and imaginary part of dielectric function, spectrum of energy loss, refractive index, extinction coefficient, and absorption coefficient) are investigated based on the density functional theory. The results obtained from the optical properties of the nanosheet show the anisotropy of this compound, especially at low and middle energies. The behavior of the dielectric function of this material is like a semiconductor material. The main peaks of the imaginary part of dielectric function for in-plane and nanotube growth directions start from low energies up to about 6 eV. The optical transmissions below the Fermi level are associated with the p-orbitals for the As, Ge, and S atoms and above the Fermi level to the p-orbitals of the Se and As atoms. Our results show that the highest reflectance for both in-plane-direction at the energy of 5.66 eV is 46%.

Plasmonic nanoantennas provides a flexible platform for manipulating the interactions of matter and light at the subwavelength scale, and opens up new avenues for the design of high-performance optical devices. In this paper, we propose a broadband and polarization-independent absorber based on tungsten (W) as a refractory plasmonic metal. This three-layer nanostructure comprises of a thick tungsten film, a thin spacer of SiO2 with high-k dielectric on which a periodic array of tungsten octagram nanoparticles is deposited. The presence of several plasmonic polaritons with low decay rates in the proposed nanostructure provides a wide bandwidth from 250 to 1940 nm with more than 90% absorptivity. The bandwidth can be tailored by altering the thickness of the insulation layer and geometric dimensions of the nanoantennas. The proposed structure benefits from a planar, low profile and small footprint, and its optical characteristic is stable in a wide range of incident angle regardless of the polarization of the incident light. These features make the proposed metasurface a suitable candidate for high-efficiency conversion of solar energy in solar thermophotovoltaic systems.

In this research Double perovskite BiCr1-xCoxO3 (BCCO) with x=0, 0.15, 0.3, 0.5 (BCCO, BCO-15CO, BCO-30CO, BCCO) Thin films were prepared by Sol-Gel and spin coating method. The formation of crystal phase was investigated using X-ray diffraction. Ultraviolet-visible spectroscopy was used to determine the band gap of these materials. The results show that by increasing the percentage of cobalt in the samples, an indirect band gap is formed in them, which is much smaller than the direct gap and increases the adsorption. The experimental results obtained are consistent with theoretical research on the optical properties of this material.

Geometry, stability, electronic structure, and absorption spectrum of Silicon nanocrystals Si24H12 and Si26H12 were investigated using density functional theory. The results showed that nanocrystals Si26H12 is more stable thanSi24H12 by 9.14 eV, where this stability can be related to the electron delocalization and aromatic behavior of proposed nanocrystals Si26H12.To investigate the nanocrystals' aromaticity properties the NICS, PDI, and PLR indexes were used. The results indicate that Si26H12 nanocrystals have aromatic properties more than benzene. Also, this structure shows a new pattern in the spectrum adsorption. This study reports relevant details for the possible synthesis of over coordinated silicon nanocrystals.

Undoped and Ag-doped ZnO nanoparticles with different percentage of Ag (2%، 4%، and6%) were synthesized by a sol-gel method using a gelatin media as a polymerization agent. Zinc nitrate and silver nitrate were used as raw materials for reaction. The obtained nanoparticles were characterized by TEM، XRD، UV-vis، and PL. The TEM results showed that، the sizes of the nanoparticles were the same approximately. The XRD patterns indicated hexagonal structure for all samples and incorporation silver ions in to the ZnO lattice. The UV-vis and PL results revealed that، the optical properties of the undoped ZnO nanoparticles were better than the Ag-doped ZnO nanoparticles.