Interband optical properties of Ni3Al

The effect of substitutional doping of Yb2+on structural, electronic, and optical properties of CsCaX3(X: Cl, Br, I) phosphors: a first-principles study

Using first-principles calculations, the effects of Yb²⁺substitutional doping on structural, electronic, and optical properties of a series of perovskite compounds CsCaX₃(X: Cl, Br, I), have been investigated. We employed generalized gradient approximation (GGA) and HSE hybrid functional to study the electronic and optical properties. A series of pristine CsCaX₃(X: Cl, Br, I) is characterized as a non-magnetic insulator with indirect bandgap perovskite materials. These phosphor materials are suitable candidates for doping with lanthanide series elements to tune their electronic bandgaps according to our requirements because of their wide bandgaps. The calculated electronic bandgaps of CsCaX₃(X: Cl, Br, I) are 3.7 eV (GGA) and 4.5 eV (HSE) for CsCaI₃, 4.5 eV (GGA) and 5.3 eV (HSE) for CsCaBr₃, and 5.4 eV (GGA) and 6.4 eV (HSE) for CsCaCl₃. According to formation energies, the Yb²⁺doped at the Ca-site is thermodynamically more stable as compared to all possible atomic sites. The electronic band structures show that the Yb²⁺doping induces defective states within the bandgaps of pristine CsCaX₃(X: Cl, Br, I). As a result, the Yb²⁺doped CsCaX₃(X: Cl, Br, I) become the direct bandgap semiconductors. The defective states above the valence band maximum are produced due to thef-orbital of the Yb atom. The impurity states near the conduction band minimum are induced due to the major contribution ofd-orbital of the Yb atom and the minor contribution ofs-orbital of the Cs atom. The real and imaginary parts of the dielectric function, optical reflectivity, electron energy loss spectrum, extinction coefficient, and refractive index of pristine and Yb²⁺doped CsCaX₃(X: Cl, Br, I) were studied. The optical dispersion results of dielectric susceptibility closely match their relevant electronic structure and align with previously reported theoretical and experimental data. We conclude that the Yb²⁺doped CsCaX₃(X: Cl, Br, I) are appealing candidates for optoelectronic devices.

Cs2NaGaBr6: a new lead-free and direct band gap halide double perovskite

In this work, we have studied new double perovskite materials, A₂¹⁺B²⁺B³⁺X₆¹⁻, where A₂¹⁺ = Cs, B²⁺ = Li, Na, B³⁺ = Al, Ga, In, and X₆¹⁻.

Ab initio study of optoelectronic and magnetic properties of Mn-doped ZnS with and without vacancy defects

The effect of vacancy defects on optoelectronic and magnetic properties of Mn-doped ZnS have been systematically investigated using first principle approaches. A single Mn substitution at Zn site induces a spin-polarized ground state in pure ZnS with total magnetization 5 [Formula: see text]. Our results for magnetic coupling show that the coupling between Mn spins in pure Mn doped ZnS is antiferromagnetic under the super-exchange mechanism. The existence of native defects has a great influence on the magnetic ground state of Mn-doped ZnS. In particular, a p -type defect such as Zn vacancy play a crucial role in stabilizing ferromagnetic ground state while n-type defect, such as S vacancy, has no effect on the magnetic ground state i.e. the interaction between two Mn spins with S-vacancy remain antiferromagnetic. Furthermore, optical properties such as dielectric functions, absorption coeffiecients, reflectivity and transmissitivity for Mn doped systems with and without vacancy defect were also studied, and we found that an absorption peak was obtained in the infrared region which is attributed to the defect states introduced by Zn vacancy in the system. In a S-vacancy defect system, the peaks in the near infrared and visible region are due to donor states introduced by S vacancy defect and these peaks are produced by electrons flipping from a spin up state to a spin down state. Finally, we also correlated the magnetic interactions with the d-d optical transition in pure Mn-doped ZnS and found that the d-d transitions during optical absorptions are red shifted and blue shifted in FM and AFM coupled Mn ions pair, which is in good agreement with the experimental observations. This study may help to understand the behavior of optical and magnetic properties of DMS under vacancy defects.

Optoelectronic and magnetic properties of Mn-doped and Mn-C co-doped Wurtzite ZnS: a first-principles study

In order to meet the requirement of spintronic and optoelectronic, we have systematically investigated the effect of Mn doping and co-doping of Mn with C on the electronic, magnetic and optical properties of wurtzite zinc sulfide (ZnS) using first principle calculations. Our results find that single Mn doping alters the non-magnetic ZnS to a magnetic one and keeps its semiconducting and a semiconductor to half-metal transition is observed for Mn-C co-doping. Furthermore, an antiferromagnetic (AFM) and ferromagnetic (FM) ground states are favorable for Mn-doped and Mn-C co-doped system, respectively. Additionally, the optical properties of our studied configuration have been calculated in terms of real and imaginary parts of the complex dielectric function, absorption coefficient, and reflectivity. The absorption edge shifts slightly toward lower energy and intensity of the main peak become weak for single Mn doping, and a sharp peak at low energy is observed for the Mn-C co-doping. The analysis of optical absorption of Mn ions doped system shows the blue- and red-shifts of the d-d transition in the AFM and FM coupled of Mn ions doped configuration, respectively which is in good agreement with the experimental observations. The improved magnetic and optical properties of Mn-C co-doped ZnS shed light on the future application of such kind of materials in spintronic and optoelectronic devices such as remote sensing and photovoltaics.

Systematic study of room-temperature ferromagnetism and the optical response of Zn1-x TM x S/Se (TM = Mn, Fe, Co, Ni) ferromagnets: first-principle approach

The structural, magnetic and optical characteristics of Zn_1-x TM _x S/Se (TM  =  Mn, Fe, Co, Ni and x  =  6.25%) have been investigated through the full-potential linearized augmented plane wave method within the framework of density functional theory. The optimized structures have been used to calculate the ferromagnetic and the antiferromagnetic ground-state energies. The stability of the ferromagnetic phase has been confirmed from the formation and the cohesive energies. The Heisenberg model is used to elucidate the Curie temperature (T _c) of these alloys. From the band structures and density of states plots, it has been observed that TM-doped ZnS/Se alloys appear to be semiconductors and exhibit ferromagnetism. In addition, the observed ferromagnetism has also been explained in terms of direct exchange energy Δ _x (d), exchange splitting energy Δ _x (pd), crystal-field energy (E _crys), exchange constants (N ₀ α and N ₀ β) and magnetic moments that shows potential spintronic applications. The optical behaviors of these alloys have been explained in terms of real and imaginary parts of the dielectric constant ε(ω), refractive index n(ω), extinction coefficient K(ω), reflectivity R(ω) and absorption coefficient σ(ω), in the energy range 0-25 eV. The calculated static limits of the band gaps and real part of the dielectric constants satisfy the Penn model. The critical limits of the imaginary part of the dielectric constants and absorption coefficients indicate that these alloys can be operated in the visible and the ultraviolet region of the electromagnetic spectrum; therefore, make them important for optoelectronic applications.

Density functional calculation for Li2CuSn as an electrode material for rechargeable batteries

The all electron full potential linearized augmented plane wave method has been used for an ab initio theoretical study of the band structure, density of states and electron charge density, and the spectral features of the linear and nonlinear optical susceptibilities for the host CuSn and Li(2)CuSn compounds. We have calculated the density of states at Fermi energy and the electronic specific heat coefficient (gamma). The total charge densities in the (100) and (110) planes were calculated. We noticed that inserting Li into CuSn leads to give two structures in the spectral features of the linear optical susceptibilities while the host compound gives only one structure. Insertion of Li into CuSn leads to breaking the symmetry resulting in noncentrosymmetric material. We have calculated the complex second-order nonlinear optical susceptibility tensor for the intercalated compound.