جستجوی مقالات مرتبط با کلیدواژه « Optical Properties » در نشریات گروه « علوم پایه »

In this work, the structural, optical and photocatalytic properties of Cu1-3xNixZn2xFe2O4 ferrites prepared by citrate-nitrate method were investigated. The samples were characterized by X-ray diffraction (XRD) and UV-Vis spectrometer at room temperature. Examining the XRD patterns indicates the presence of a spinel structural phase transition from a tetragonal to cubic structure, which shows an increase in symmetry with the co-substitution of Ni and Zn in the copper ferrite. The bandgap values of the samples show a minimum value of 1.43 eV for x = 0.05. The highest catalytic activity of 95% in the degradation of methylene blue is obtained for the x = 0.05 sample due to its smaller energy gap.

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 research, we investigate and compare the optical properties of lead borate and bismuth borate glasses. We used the Refractive index and the energy band gaps determined experimentally in Ref [22]. We found that molar refraction and electronic polarizability demonstrate similar behavior. The metallization varies from 0.630 to 0.568 for lead borate glasses and from 0.526 to 0.435 for bismuth borate glasses with increasing PbO/Bi2O3 content. The transmission coefficient decreased from 0.884 to 0.846 for PbB glasses and from 0.818 to 0.751 for BiB glasses, while the dielectric constant increased from 2.755 to 3.276 for PbB glasses and from 3.094 to 4.884 for BiB glasses. The optical electronegativity decreased from 0.964 to 0.792 for PbB and from 0.857 to 0.760 for BiB. The linear dielectric susceptibility increased from 0.139 to 0.181 for lead borate glasses and from 0.214 to 0.309 for bismuth borate glasses. The nonlinear optical susceptibility changed from 0.647  to 1.829  esu for PbB and from 0.359  to 1.551  esu for BiB , indicating more than fivefold increment. The nonlinear refraction index varied from 1.470  to 3.810  esu for lead borate glasses and from 0.704  to 2.646  esu for bismuth borate glasses. The results confirm that bismuth borate is better than lead borate for optical applications.

In the LDA approximation with the pseudo-potential method, and from the density of states diagram, the value of the band gap are 1.2 eV, 1.4 eV, and 2.37 eV, in the LDA and LDA+U and HSE approximations, respectively, were obtained with norm conserving pseudo-potential. Also, the calculated bulk moduls value were 81 GPa in LDA, 79.4 GPa in LDA+U, and 76.5 GPa in HSE approximation. Finally, the optical properties were computed, such as refractive index, extinction coefficient, absorption coefficient, reflection coefficient and optical conductivity. From the examination of the optical properties, the optical gap value obtained from the absorption coefficient is in good agreement with the band gap value, which is Optical coefficients are different in different directions due to the anisotropy of the structure. The value of the optical gap that read from the absorption coefficient diagram in the approximation of LDA, LDA+U and HSE was 1.27 eV, 1.4 eV and 2.37 eV, respectively. Based on the optical investigations, this compound is useful in solar cells and optoelectronic materials.The value of the optical gap that read from the absorption coefficient diagram in the approximation of LDA, LDA+U and HSE was 1.27 eV, 1.4 eV and 2.37 eV, respectively.

In this study, the optical and electronic properties of bulk and nano-layer of zinc selenide (ZnSe) and zinc sulfide (ZnS) are investigated. The calculations for solving the many-body Schrodinger equations are performed in the framework of density functional theory using the WIEN2K computational package. The Engel-Vosko and gradient generalized approximation (GGA) treat the exchange-correlation potential. To investigate the electronic and optical properties of zinc selenide and zinc sulfide nano layers, the electronic band structure and the real and imaginary parts of complex dielectric function for the bulk and nano-layer with different thicknesses are calculated and compared. The results of electronic band structures show that the energy band gap of zinc selenide and zinc sulfide nano-layers with various thicknesses decreases to zero and are metal. In contrast, the bulk of zinc selenide and zinc sulfide compounds are semiconductors. The results also show that for each compounds the static dielectric function for the perpendicular and parallel direction to the nano-layer surface is different from the bulk static dielectric function. Comparison between the real parts of complex dielectric function for the bulk and nano-layer shows that absorption of electromagnetic radiation for the ZnSe and ZnS nano-layer in comparison to corresponding bulk results occur in lower energies.

In this paper, the thermo-electric, phonon, electronic, and optical properties of the C3N monolayer have been investigated using the Wien2K computational code based on first principles calculations in the framework of the density functional theory. The study of electronic properties shows the behavior of non-magnetic semiconductors with an indirect gap with a value of 0.5 electron volts for this two-dimensional structure. Also, optical properties such as dielectric function, reflection, energy loss function, absorption coefficient, and optical conductivity are calculated. C3N monolayer is optically anisotropic in z and x direction, which according to the refractive index diagram leads to birefringence, which is a key parameter for this compound's linear optical performance. The results provide a fundamental understanding of the design of composite structures used in nanodevices based on two-dimensional advanced materials. The linear response approach along the symmetric points calculates the phonon dispersion diagram. The results indicate the absence of negative modes in the phonon spectrum, indicating that the structure is dynamically stable. Investigating the thermoelectric properties of the C3N monolayer using the semi-classical Boltzmann theory shows that this monolayer has a value coefficient (ZT) close to one at room temperature and temperatures lower than room temperature. As a result, it can be proposed as a candidate for thermoelectric applications.