Optical Properties Of Co Research Articles

Structural, morphological, and optical properties of Co and (Co, Fe) co-doped Zn2SnO4 nanoparticles prepared by hydrothermal method for antibacterial activity

Structural, morphological, and optical properties of Co and (Co, Fe) co-doped Zn2SnO4 nanoparticles prepared by hydrothermal method for antibacterial activity

Tuning of the ferroelectric and optical properties of ZnSnO3 with transition metals: Mn, Cr and Co

Using an approach based on the density functional theory, the electronic, polarization, structural, and optical properties of Co, Cr and Mn doped ZnSnO3 were studied. The analysis of the structural properties shows that the introduction of magnetic ions produces antiparallel magnetic states and reduces the band gap as compared with the gap of pristine ZnSnO3. Additionally, the results reveal the persistence of polarization after doping, reaching a maximum polarization value of 44.94 μC/cm2 for 12.5 % Co-doped ZnSnO3. These results highlight the importance of ZnSnO3 as a candidate material for solar energy harvesting, by combining a reduced gap and significant spontaneous polarization.

Electronic, magnetic and optical properties of Co(II) doped and (Al, Co) co-doped CdS nanowires: An ab initio study

In this work, we have carried out first-principles calculations for understanding the optoelectronic and magnetic properties of Co(II)-doped and (Al, Co) co-doped CdS nanowires. In the free carrier Co(II)-doped CdS NW, the spin-down Co(II)-ta state is completely empty, leading to a super-exchange process. The exchange coupling of the electron carrier (provided by Al co-doping) with the spin-down Co(II)-ta state promote a ferromagnetic ordering via double exchange interactions with a Curie temperature above room temperature. From the optical analysis, we found that Co(II) doping causes a blue-shift of the fundamental energy gap of CdS nanowire. The observed d-d spin-allowed transition peak of the Co(II) ion at 1.97 eV in the visible region is consistent with the experiments. The n-type Al co-doping not only generates an exciton-magnetic polaron (EMP) peak next to the fundamental bandgap but also exhibits the red-shift of the fundamental energy gap and Co(II)'s d-level-to-d-level transition bands. The correlation between spin-spin interaction and optical absorption shows that the d-d spin-allowed transition and optical energy gap both exhibit a blue-shift (red-shift) in the AFM (FM), supporting the experimental observation. Due to the paramagnetic behavior of the Co ions in the far configuration, there is no shift in the d-d transition peak or optical bandgap in the AFM and FM.

Structural, electrical, magnetic & optical properties of Nickel, cobalt doped and Co-doped wurtzite GaN: A first-principle investigation

The structural, electronic, magnetic, and optical properties of Co (6.25%) and Ni (6.25%) monodoped and co-doped GaN were calculated by the DFT+U method using a 2 × 2 × 2 supercell of a total of 32 atoms. The formation energy was negative under both Ga-rich and N-rich conditions for all structures. N-rich condition is found to be favorable for GaN growth. The electronic and magnetic properties changed after doping due to the transition of the 3 d states of Ni, Co and hybridization of 2p of N. Hence monodoped GaN is ferromagnetic whereas the co-doped one is ferrimagnetic due to partial cancellation by the opposite spin of Ni and Co. The doped and co-doped absorption peaks are blue-shifted in the ultraviolet (UV) and redshifted in the visible-infrared (VIS-IR) region from the peaks of pure GaN. A pronounced absorption of VIS-IR is observed in monodoped structures. Both dielectric constant and refractive index increased due to co-doping whereas monodoping had enhanced the properties significantly. This theoretical study suggests the potential application of the Co, Ni monodoped in VIS- IR photonic and co-doped GaN in spintronic devices.

Magnetic and Spin‐Polarized Optical Properties of Co and Mn Adsorbed γ‐GeSe

The structural, electronic, magnetic, and optical properties of Co‐ and Mn‐adsorbed γ‐GeSe have been studied comprehensively via first‐principles density functional calculations. It is found that the most stable adsorption configuration is that Co and Mn are on the top of the hexagonal hollow in the second Ge layer. After Co and Mn adsorption, γ‐GeSe becomes magnetic with 1 μB and 3 μB magnetic moment, which mainly comes from mainly the Co(Mn)‐d, Ge‐s, Ge‐p, and Se‐p states. In particular, the optical absorption in the low‐energy range is greatly enhanced by Co and Mn adsorption and results in interesting spin‐dependent absorption in low‐energy region due to the strong electron transition at the spin‐down channel, which makes them attractive candidates for spin‐optoelectronic devices.

A simulation study on the electromagnetic structure and optical properties of Co doped TiO2

Rutile TiO2 with intrinsic defects or doped by specific elements will emerge excellent electromagnetic property and optical characteristics, such as room temperature ferromagnetism. In this study, we studied the effects of intrinsic defects and Co atoms on the electromagnetic structures and optical properties of rutile TiO2 by Density Functional Theory. The results show that the magnetic moment is produced by intrinsic defects such as VO and Tii while the Co atom can also polarize the system. The magnetism of Co doped TiO2 does not come entirely from Co atom. There will be a change in charge population when O and Ti are close to Co atoms, which will produce local spin magnetic moment. The hybridization of Co:3d, Ti:3d and O:2p orbitals leads to the generation of new impurity levels in the band gap, which reduces the Eg of rutile TiO2 and improves the visible light absorption, resulting in the red-shift of the light absorption edge of Co doped TiO2. In addition, the optical properties of both pure rutile TiO2 and Co doped TiO2 are anisotropic, especially along [001] direction.

Effect of ‘Zn’ substitution on structural, morphological, magnetic and optical properties of Co–Zn ferrite nanoparticles for ferrofluid application

Effect of ‘Zn’ substitution on structural, morphological, magnetic and optical properties of Co–Zn ferrite nanoparticles for ferrofluid application

Structural, morphological, and optical properties of Co‐ substituted Zn2SiO4 nanopowders prepared by a hydrothermal-assisted sol-gel process

Cobalt-substituted zinc orthosilicate pigments were obtained by pyrolysis of precursors synthesized by a convenient hydrothermal-assisted sol-gel process without using any toxic or expensive chemical (e.g., silicon alkoxides). XRD investigation confirms that the Co2+ ions are successfully incorporated into the Zn2SiO4 crystal. Rietveld refinement data reveals that unit-cell parameters increase with Co-content in Zn2-xCoxSiO4 solid-solutions. The homogeneous pigments are composed of largely agglomerated primary particles having a size less than 70 nm. The UV–visible spectroscopy shows that the blue color of pigments is caused by the presence de Co2+ in tetrahedral sites of Zn2+. The colorimetric parameters indicate that a blue pigment could be achieved with the only x = 0.05. A content of less than 5 wt% of the prepared pigments gives a deep blue hue to ceramic glazes. Cobalt-substituted Zn2SiO4 pigments exhibit high coloring performance and a relatively less cobalt content, which make them promising pigments for ceramic tiles.

Ab-initio calculations on structural, electronic, half-metallic and optical properties of Co-, Fe-, Mn- and Cr-doped $$\hbox {Ba}_{{\mathbf {2}}}\hbox {LuTaO}_{{\mathbf {6}}}$$

Ab-initio calculations on structural, electronic, half-metallic and optical properties of Co-, Fe-, Mn- and Cr-doped $$\hbox {Ba}_{{\mathbf {2}}}\hbox {LuTaO}_{{\mathbf {6}}}$$

The first principle study of magnetic, electronic, and optical properties of Co- and Mn-doped boron nitride nanosheets

In the present study, the magnetic, electronic, and optical properties of Co- and Mn-doped BN nanosheets [substituting one Mn(Co) atom on B (MnB or CoB), N (MnN or CoN), or two Mn(Co) atoms with B and its adjacent N atom (MnBN or CoBN) sites] for both perpendicular (E||c) and parallel (E||a) electromagnetic wave polarization have been investigated by the first principle calculations based on density functional theory. In this regard, optical parameters of Co/BN and Mn/BN including dielectric function, absorption, optical conductivity, extinction index, energy loss function, and reflectivity and refraction index are calculated. Magnetic investigations also show that compared to the pure BN sheet with 4.5 eV bandgap and zero magnetic moment, placing Co or Mn atom in the BN sheet decreases the bandgap and creates a net magnetic moment. Results inferred to the half-metallic behavior of MnB/BN and CoB/BN, and other doped structures become n-type semiconductor with a narrow bandgap. As can be seen, the optical and magnetic properties of Co- and Mn-doped BN monolayer improve their applications in the industry such as designing spintronic and optoelectronic devices.

Adsorbed of toxic gas molecules (CO, H2S, and NO) on alkali-metal-doped g-GaN monolayer

Using the first-principles calculation, based on density functional theory, the geometric structures, electronic, magnetic, and optical properties of CO, H2S, and NO toxic gas molecules adsorbed on alkali metals (Li, Na, K, Rb, and Cs) doped g-GaN monolayer have been investigated. The adsorbed systems have induced magnetic property except H2S adsorbed on Na doped g-GaN monolayer, the total magnetic moment of CO, H2S, and NO adsorbed on alkali metals doped g-GaN are 2.0, 2.0, and 1.0 μB, respectively, and the materials are spin semiconductors. The charge transfer mainly occurs between gas molecules, doped atoms, and Ga atoms. The adsorbed behaviors of CO, H2S, and NO adsorbed on intrinsic g-GaN are physisorption, H2S adsorbed on Na doped g-GaN monolayer and NO adsorbed on Li, Na, K, Rb, and Cs doped g-GaN monolayer are chemisorption, while CO adsorbed on alkali metals doped g-GaN monolayer are physisorption. The results show that the adsorptive properties can be enhanced dramatically by doping with alkali metals, and the materials can be used in gas sensor devices and detector devices. In addition, the adsorbed coefficients in ultraviolet and visible indicate the materials promising the application of violet and UV optoelectronic devices.

Development of the Morphology and the Band Gap Energy of Co–Si Nanofibers by Inserting Zirconium and Titanium with Dual Anions Intercalation Process

The plate-like structure is the most familiar morphology for conventional layered double hydroxides (LDHs) in case their structures consist of divalent and trivalent cations in their layers. In this study, nanofibers and nanoneedles of Co–Si LDHs were prepared for the first time. By the inclusion of zirconium inside the nanolayers of LDH structures, their plates were formed and transformed to nanofibers. These nanofibers were modified by the insertion of titanium to build again plate-like morphology for the LDH structure. This morphology controlling was studied and explained by a dual anions intercalation process. The optical properties of Co–Si LDHs indicated that the incorporation of zirconium within their nanolayers decreased the band gap energy from 4.4 eV to 2.9 eV. Following the same behavior, the insertion of titanium besides zirconium within the nanolayers of Co–Si LDHs caused a further reduction in the band gap energy, which became 2.85 eV. Although there is no data for the optical properties of Co–Si LDHs in the literature, it is interesting to observe the low band gap energy for Co–Si LDHs to become more suitable for optical applications. These results concluded that the reduction of the band gap energy and the formation of nanofibers introduce new optical materials for developing and designing optical nanodevices.

Calculated optical properties of Co in ZnO: internal and ionization transitions

Previous luminescence and absorption experiments in Co-doped ZnO revealed two ionization and one intrashell transition of electrons. Those optical properties are analyzed within the generalized gradient approximation to the density functional theory. The two ionization channels involve electron excitations from the two gap states, the triplet and the doublet, to the conduction band. The third possible ionization channel, in which an electron is excited from the valence band to the level, requires energy in excess of 4 eV, and cannot lead to absorption below the ZnO band gap, contrary to earlier suggestions. We also consider two recombination channels, the direct recombination and a two-step process, in which a photoelectron is captured by and then recombines via the internal transition. Finally, the observed increase the band gap with the Co concentration is well reproduced by theory.The accurate description of ZnO:Co is achieved after including +U corrections to the relevant orbitals of Zn, O, and Co. The value was calculated by the linear response approach, and independently was obtained by fitting the calculated transition energies to the optical data. The respective values, 3.4 and 3.0 eV, agree well. Ionization of Co induces large energy shifts of the gap levels, driven by the varying Coulomb coupling between the electrons, and by large lattice relaxations around Co ions. In turn, over ∼1 eV changes of levels induced by the internal transition are mainly caused by the occupation-dependent corrections.

The electronic, magnetic and optical properties of Co doped marcasite FeS2

The electronic, magnetic and optical properties of Co doped marcasite FeS2 compounds have been investigated through the first-principles calculations. No imaginary frequency emerges in the phonon dispersion curves confirms the Fe7CoS16 and Fe6Co2S16 compounds are dynamical stable. Although the pure Fe8S16 compound is a nonmagnetic semiconductor with band gap of 1.17 eV, the Fe7CoS16 compound changes to a magnetic semiconductor with a very narrow band gap of 0.106 eV, the Fe6Co2S16 compound changes to a half-metal with half-metal band gap of 0.37 eV in spin-down channel. For all three considered configurations of the Fe6Co2S16 compound, the ferromagnetic state is preferred over antiferromagnetic state, especially for smaller separation distance of two doped Co atoms. The higher Curie temperatures than room temperature indicates the Fe6Co2S16 compound is a promising candidate for spintronics applications. In addition, the calculated optical properties shows that Fe7CoS16 and Fe6Co2S16 compounds have stronger absorption than Fe8S16 compound when the wavelength more than 500 nm, which suggests the compounds are potential candidates for solar cells.

Novel substitutional effects on optical properties of Cds:Co system (A theoretical study)

In current study, we calculate optical properties of Co doped CdS system for pure CdS and for 2 × 2 × 2 supercell configuration with two types of substitutions; Cd substitution and interstitial substitution accompanied by creating sulfur vacancy. Graphical trends for optical properties are almost similar except in case of interstitial substitution where quantum mechanical effects are particularly observed and curve shows slight different behavior. Study reveals that optical properties are enhanced and absorption increases in visible region. Effect of Co doping within CdS host lattice demonstrates that electro-optical properties are enhanced.

Structural and optical properties of Co and Ni doped ZnO thin films prepared by RF magnetron sputtering

We have reported the effect of Co and Ni doping on structural and optical properties of ZnO thin films prepared by RF reactive sputtering technique. The composite targets were formed by mixing and pressing of ZnO, Mn3O4, CoO and NiO powders. The thin films were deposited on sapphire, quartz and glass substrates. The structure study confirms the formation of the hexagonal wurtzite ZnO without any secondary phase in transition metal (Co, Ni) - doped samples. Cross-sectional TEM images of all studied samples show a denseand uniformly textured structure composed of column-like structure along the growth direction. The surface morphology of the thin films was studied using atomic force microscopy (AFM). Different surface morphology (AFM) images were obtained depending on the film composition and growth conditions. Optical absorption spectra suggest of substitution Zn2+ ions in ZnO lattice by transition metal atoms. The shift of the absorption edge due to decrease the energy band gap with increasing cobalt content and complex dependence of the energy band gap on content of nickel was observed in optical absorption spectra of the studied films. The room temperature photoluminescence peaks are attributed to near band gap emission and vacancy or defect states.

Structural, electrical and optical properties of sol-gel synthesized cobalt substituted MnFe2O4 nanoparticles

We report the structural, electrical and optical properties of Co substituted manganese ferrite of the composition Mn1−xCoxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5) synthesized by sol-gel technique. X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structure. The average crystallite size of these materials is found to be in the range of 20–35nm and lattice constant is found to decrease as Co2+ concentration is increased. The permittivity (ɛ), dielectric loss (tanδ) and ac conductivity (σac) have been determined at room temperature as a function of frequency (42Hz to 5MHz). The results of dielectric properties indicate the normal Maxwell-Wagner type dielectric dispersion due to interfacial polarization. DC electrical resistivity has been performed using two probe technique. The decrease of resistivity with temperature confirms the semiconducting nature of the samples. Real and imaginary part of impedance ( Zʹ and Zʺ) suggest existence of one relaxation mechanism which is attributed to the co-effect of grains and grain boundaries. The energy band gap as determined from the UV–visible spectra decreases gradually with the Co increasing content.

Fabrication and spectral properties of hot-pressed Co:MgAl2O4 transparent ceramics for saturable absorber

Cobalt-doped magnesium aluminate spinel (Co:MgAl2O4) could be the most effective saturable absorber (SA) for Q-switching solid-state lasers operating at 1.5 μm. Using LiF as the sintering aid, highly transparent Co:MgAl2O4 ceramics were fabricated by hot pressing (HP) of the commercial spinel and the co-precipitated Co:MgAl2O4 powder mixture. The optical properties of Co:MgAl2O4 ceramics were investigated, and the ground state absorption cross section (σgas) of Co2+ was calculated from the curve of the absorption coefficient. For the Co:MgAl2O4 ceramics hot-pressed at 1600 °C for 2 h under 30 MPa with 1 wt.% LiF addition, the in-line transmittance reaches about 77% at 1000 nm and 1700 nm, and the ground state absorption cross section of Co2+ is 2.55 × 10−19 cm2 at the wavelength of 1540 nm, which is promising as a saturable absorber for solid-state pulse laser operating at 1.5 μm.

DFT study of elastic, half-metallic and optical properties of Co2V(Al, Ge, Ga and Si) compounds

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.

Synthesis and Optical Properties of Co and Zn-Based Metal Oxide Nanoparticle Thin Films

Synthesis and Optical Properties of Co and Zn-Based Metal Oxide Nanoparticle Thin Films