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Inorganic, non-toxic metal halide perovskites are the benchmark for optoelectronic device commercialization. Due to their significant importance, the density functional theory-based ab initio method was engaged to study the fundamental physical properties of metal halide perovskites TlBX3 (B = Ge, Sn; X = Cl, Br, I). The studied lattice constants and volume are different from the chosen systems, and the crystal stability is also justified in particular. Among six studied compounds, Sn-based compounds show lower band gaps than Ge-based compounds, where I at site X shows the lowest band gaps. The illustration of the density of states and the specific projection of the electronic contribution of atomic orbitals were added to verify the actual semiconducting electronic behavior. The presence of dual chemical bonds is confirmed by bond length statistics and charge density distribution. The optical properties vary among the compounds, and there is an opposite behavior between low and high-energy regions. TlGeX3 has a higher Young modulus, bulk modulus, and shear modulus than TlSnX3, whereas the hardness and anisotropic behavior are lower than TlSnX3. In this investigation, three-dimensional diagrams of elastic moduli have been depicted using the ELATE tool, which facilitates the easy identification of anisotropic elastic properties. Furthermore, this study will shed light on how to fabricate lead-free inorganic perovskites for use in optoelectronics.

Upon studying the optical properties of solid solutions of p-type Bi2Te3–Sb2Te3 in the infrared range, it is found that in the single crystal Bi0.6Sb1.4Te3, deformation of the reflection-coefficient spectra is observed in the frequency range of observation of the plasma resonance of free charge carriers. Deformation of the plasma edge increases with a decrease in temperature. Using the Kramers–Kronig dispersion relations from experimental reflection spectra, the spectral dependences of the real ε1 and imaginary parts ε2 of the permittivity function, as well as the energy-loss function characterizing the rate of energy dissipation, are calculated. Splitting of the peak of the energy loss function is found, which indicates the effect on the plasma resonance from another process occurring in the electronic system. It is established that such a process is the transition of electrons between nonequivalent extrema of the valence band. Convergence of the collective and single-particle energies of the electronic system leads to amplification of the electron—plasmon interaction, which is the most probable cause of the observed deformation of the plasma edge. [ABSTRACT FROM AUTHOR]

Under varying hydrostatic pressures ranging from 0 to 150 GPa, first-principles calculations were conducted to investigate the structural, electronic, bonding, optical, elastic, and mechanical characteristics of the Lead (Pb)-free halide perovskite FrCaCl3 using both the GGA and hybrid HSE06 parameterized density functional theory (DFT). Since the FrCaCl3 cubic perovskite has not yet been synthesized experimentally, its structural and thermodynamic stabilities are confirmed by the Goldschmidt tolerance factor, the octahedral factor, and the formation energy. The induction of pressure has caused a simultaneous decrease in both the lattice parameters and the electronic band gap. Applying the hybrid HSE06 potential refines the accuracy of the band gap, with values decreasing from 5.705 to 2.618 eV from 0 to 150 GPa pressure, suggesting improved optoelectronic attributes. Employing pressure facilitates the formation of stronger chemical bonds characterized by reduced bond lengths. The investigation of optical functions demonstrates that with increased pressure ranging to 150 GPa, the optical conductivity along with the absorption coefficient is oriented towards the low-energy region. The FrCaCl3 perovskite has the prospect to be used in X-ray imaging and other fields of nuclear medicine and diagnostics as it contains the radioactive element Francium (Fr). Additionally, it is found via the study of mechanical characteristics that FrCaCl3 is mechanically stable under various applied pressure, and adding pressure makes it more ductile as well as more anisotropic.

Intending to advance the use of halide-perovskites in technological applications, in this research, we investigate the structural, electronic, optical, and mechanical behavior of metal-halide perovskites ACaCl3 (A = Cs, Tl) through first-principle analysis and assess their potential applications. Due to the applied hydrostatic pressure, the interaction between constituent atoms increases, thereby causing the lattice parameter to decrease. The band structure reveals that band gap nature transits from indirect to direct at elevated pressure. Moreover, at high pressure, the electronic band structure shows a notable band gap contraction from the insulator (>5.0 eV) to the semiconductor region, which makes them promising for electronic applications. The charge density map explores the ionic and covalent characteristics of Cs/Tl–Cl and Ca–Cl under pressured and unpressurized environments. Induced pressure enhances the optical conductivity as well as the optical absorption that moves toward the low-energy region (red shift), making ACaCl3 (A = Cs, Tl) advantageous for optoelectronic applications. Additionally, this study reveals that the mechanical properties of ductility and anisotropy were found to be improved at higher pressures than in ambient conditions. Overall, this study will shed light on the technological applications of lead-free halide perovskites in extreme pressure conditions.

A method for measuring the optical functions of a flat sample made of homogeneous and isotropic material, using attenuated total reflection spectroscopy when there is poor contact between the sample and the internal reflection element is presented. The approach consists in treating the spacing between the internal reflection element and the sample as an adjustable parameter, along with the dispersion model parameters, in the simultaneous fitting of s - and p -polarized spectra obtained when the gap distance is unknown. The method is tested with both synthetic and experimental (polystyrene) spectra. The results demonstrate the method's ability to accurately determine the optical functions even in the presence of a contact problem. Graphical Abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

In this study, we report for the first time the results of ab initio calculations of the electron band energy structure and optical properties for thin films of solid-state solution CdSe1–xSx (x = 0, 0.25, 0.50, 0.75 and 1.00) with the interaction of their surface with H2 and NO2 molecules. It is practically important concerning the problem of developing new gas sensors and for the photocatalytic hydrogen (H2) evolution. Concentration dependences of the energy gaps, the position of an energy level of the valence band, and the conduction band are studied. Interaction of the thin films with H2 creates a tendency to decrease the band gap and transform its concentration dependence to a quasi-linear one. The concentration dependences of optical properties are mainly studied on the example of refractive index at the light wavelength 500 nm. Moreover, we elucidate the influence of adsorption of the H2 and NO2 gas occurring on the surface of CdSe1–xSx thin films on their optical functions. [ABSTRACT FROM AUTHOR]

In this study, we report for the first time the results of ab initio calculations of the electronic energy spectra and optical functions for the thin films of solid-state solution CdSe1–xSx (x = 0, 0.25, 0.50, 0.75 and 1.00). A case of interaction of these films with CO molecules is also considered, which is practically important in relation to the problem of developing new CO sensors. Concentration dependences of the energy gaps associated with the main optical transitions in CdSe1–xSx, Г8v–Г6c and Г7v–Г6c (levels in the Г point of Brillouin zone; v and c subsymbols correspond to the valence band and conduction band, respectively), are studied and a spin–orbit decoupling is evaluated. It is demonstrated that the concentration dependences of these energy gaps are quadratic, with a characteristic 'bending' parameter equal to 0.13 and 0.12, respectively, for the Г8v–Г6c and Г7v–Г6c transitions. Interaction of the thin films with CO imposes a tendency to increasing bandgap and transforming its concentration dependence to linear one. It is also revealed that the above interaction corresponds to exothermic adsorption processes and the corresponding adsorption energy is determined. The concentration dependences of optical properties are mainly studied on the example of refractive index at the light wavelength 500 nm. Moreover, we elucidate the influence of adsorption of CO gas occurring on the surface of CdSe1–xSx thin films on their optical functions. Finally, the electronic band structure and the main optical properties obtained theoretically in this work are compared with the experimental data known from the literature, which reveals a fair agreement with the experiment. [ABSTRACT FROM AUTHOR]

Comprehensive modeling of non-polarized infrared attenuated total reflection spectrum based on Fresnel equations and wavenumber-dependent dielectric function models of isotropic materials is shown to be a suitable and easy methodology to retrieve optical functions. The scheme is completely general and can be used even for strong dispersion and absorption resonances. Attenuated total reflection spectra in liquid water, measured in the spectral region 100–4400 cm−1 with diamond and germanium as internal reflection elements, were used to illustrate and evaluate the method. The refractive index of water computed from the dispersion analysis is critically compared with literature data. Graphical Abstract [ABSTRACT FROM AUTHOR]

This study carries out density functional theory (DFT)‐based simulation in order to observe the effect of pressure (up to 120 GPa) on the various physical properties of boron (B) containing new MAX compounds Hf2InB2 and Hf2SnB2. Structural parameters in ambient conditions show excellent concordance with prior experimental and theoretical data. A decreasing trend of lattice parameters with pressure is observed. The stability of the phases under pressure is determined by calculating the elastic constant using the Born stability criteria, and is found stable within the studied pressure range. Pressure's effect on the various elastic moduli is considered, and a linear response with pressure is observed. The brittle/ductile behavior under pressure is investigated, and a brittle to ductile phase transition is found. An opposite trend of elastic moduli with pressure is observed for Vickers hardness. The nonlinear variation of Vickers hardness with pressure has been interpreted in terms of Pugh ratio and density of states (DOS). A decreasing trend of the anisotropic indices is observed for Hf2InB2, while an increasing trend is observed for Hf2SnB2. The electronic and optical properties are also significantly influenced by the pressure. The results obtained at zero GPa have been compared with previous results and show significant agreement. [ABSTRACT FROM AUTHOR]

Optical functions and transitions are essential for a material to reveal the light–matter interactions and promote its applications. Here, we propose a quantitative strategy to systematically identify the critical point (CP) optical transitions of 2D semiconductors by combining the spectroscopic ellipsometry (SE) and DFT calculations. Optical functions and CPs are determined by SE, and connected to DFT band structure and projected density of states via equal-energy and equal-momentum lines. The combination of SE and DFT provides a powerful tool to investigate the CP optical transitions, including the transition energies and positions in Brillouin zone (BZ), and the involved energy bands and carries. As an example, the single-crystal monolayer WS2 is investigated by the proposed method. Results indicate that six excitonic-type CPs can be quantitatively distinguished in optical function of the monolayer WS2 over the spectral range of 245–1000 nm. These CPs are identified as direct optical transitions from three highest valence bands to three lowest conduction bands at high symmetry points in BZ contributed by electrons in S-3p and W-5d orbitals. Results and discussion on the monolayer WS2 demonstrate the effectiveness and advantages of the proposed method, which is general and can be easily extended to other materials. [ABSTRACT FROM AUTHOR]

Electronic and phonon band structure, thermodynamic and optical properties are studied for the CdTe crystal. We calculated the electron and phonon dispersion at high symmetry directions, density of electron and phonon state, temperature dependence feature of Raman spectra, heat capacity, free energy, entropy, enthalpy and Debay temperature estimated with the generalized gradient approximation (GGA). A Perdew–Burke–Ernzerhof functional (PBE) was utilized. To study the optical properties was use a complex dielectric function ε(ħω). All of the calculated parameters correlate well with the known experimental data.

In recent times, ABX3 halide perovskite materials have emerged as revolutionary components in photovoltaic solar cells, functioning as photoabsorbers. Recently, there has been significant research attention directed towards lead halide perovskites. Nevertheless, there is ongoing research to identify lead-free alternatives due to the toxicity of lead. Therefore, the present study utilizes density functional theory to investigate the physical characteristics of the lead-free halide perovskites GaXCl3 (where X represents Ca, Sr, and Ba). The study aims to assess the feasibility of GaXCl3 (X = Ca, Sr, and Ba) for use in optoelectronic applications through an analysis of its structural, electrical, optical, and mechanical properties. The band gaps of GaCaCl3, GaSrCl3, and GaBaCl3 compounds have been found to be 3.45 eV, 3.22 eV, and 2.92 eV, respectively, which correspond to higher indirect band gaps. Additionally, elastic constants were computed in order to gain insight into the mechanical characteristics of the substance. The results reveal that all three compounds exhibit positive elastic constant Cij values, demonstrating their mechanical stability. However, their phonon dispersion curves show some negative parts which indicate their dynamic instability with temperature. Considerable performance in optoelectronic technology can be deduced from the absorption and optical conductivity of ultraviolet and visible light. [ABSTRACT FROM AUTHOR]

This article investigates the physical properties of lead-free tin- and germanium-based halide perovskites under pressure via the density functional theory to use as potential photovoltaic materials. Specifically, the structural, electronic, optical, and mechanical properties of KMCl3 (M = Ge, Sn) under diverse hydrostatic pressures ranging from 0 to 8 GPa are examined to vindicate the compounds' superiority for useful applications. The structures show high precision in terms of lattice constants, which approves the formerly published data. The calculated lattice constant (5.261 and 5.58 Å for KGeCl3 and KGeCl3, respectively, at 0 GPa) and unit cell volume (145.67 and 173.80 Å3 for KGeCl3 and KGeCl3, respectively, at 0 GPa) are significantly reduced ((lattice constant 4.924 Å (5.183 Å) and unit cell volume 119.41 Å3 (139.39 Å3) for KGeCl3 (KSnCl3) at 8 GPa) due to the pressure effect, while the cubic phase stability is maintained. Under ambient pressure, the calculated band gap reveals the compounds' semiconducting nature. Nevertheless, when pressure is increased, the band gap narrows, enhancing its conductivity and igniting its route towards semiconductor to metallic transition. The ionic and covalent bonding nature of K-Cl and Ge(Sn)-Cl, respectively; as well as the decrement of bond length due to external pressure are marked by charge density mapping. The optical functions are also enhanced when pressure is devoted, vindicating the chosen perovskites' suitability in various optoelectronic devices in the visible and ultraviolet ranges. Likewise, while maintaining mechanical stability, hydrostatic pressure significantly impacts mechanical properties. The ductility and anisotropic behavior of both perovskites are intensified under applied pressure.

In this paper, we report on optimizing the conditions for subsequently growingsingle-phase films of calcium monosilicide (CaSi) and calcium disilicide (CaSi2) on single-crystal silicon by reactive deposition epitaxy (RDE) and molecular beam epitaxy (MBE). The temperature range for the growth of CaSi films (400–500 °C) was determined, as well as the temperature range (600–680 °C) for the growth of CaSi2 films on silicon with three orientations: (111), (100) and (110). The minimum temperatures for the epitaxial growth of CaSi films by the RDE method and CaSi2 films by the MBE method were determined, amounting to, respectively, T = 475 °C and T = 640 °C. An increase in the ratio of Ca to Si deposition rates to 26 made it possible to grow a large-block CaSi2 epitaxial film with the hR6 structure by the MBE method at T = 680 °C. Raman spectra and reflection spectra from single-phase epitaxial CaSi and CaSi2 films on silicon were recorded and identified for the first time. The correspondence between the experimental reflection spectra and the theoretically calculated reflection spectra in terms of amplitude and peak positions at photon energies of 0.1–6.5 eV has been established. Single-phase CaSi and CaSi2 films retain transparency in the photon energy range 0.4–1.2 eV.

The work considered the growth, optical properties and emerging interband transitions in Ca2Si films grown on silicon substrates with (111), (001), and (110) orientations at two temperatures (250 °C and 300 °C) using the sacrificial-template method. The optimum temperature for MBE single-phase growth of Ca2Si is 250 °C. Calculations of optical functions from the transmission and reflection spectra were carried out within the framework of a two-layer model and by the Kramers–Kronig method. It is shown that the main peaks in the experimental reflection spectra and the optical conductivity calculated according to Kramers–Kronig are in good agreement with each other. Comparison of ab initio calculations of the energy band structure and optical properties of a Ca2Si single crystal and two dimensional Ca2Si layers with experimental data in the region of high energy transitions showed good coincidence.

Several bulk and thin‐film crystals of SnO2 are grown and examined using generalized ellipsometry techniques. The bulk samples are grown using the chemical vapor transport technique and thin films of SnO2 are grown using the pulsed laser deposition technique. The bulk samples are examined using the two‐modulator generalized ellipsometry microscope (2‐MGEM) at normal incidence and the spectroscopic two‐modulator generalized ellipsometer (2‐MGE). The spectroscopic optical functions of tin oxide are then obtained using the 2‐MGE from 1.46 to 6.2 eV. The material is highly birefringent, and the ordinary bandgap is less than the extraordinary band edge. 2‐MGE measurements are also made on thin‐film samples of crystalline tin oxide grown on sapphire and rutile, showing no cross polarization. Because of the complicated morphology of the tin oxide films grown on sapphire, the ellipsometry data are simulated using the Tauc–Lorentz model. Films grown on rutile had the optic axis perpendicular to the sample surface, but the film is strained, resulting in a more complicated ellipsometric spectrum. These films are modeled using the air/surface roughness/tin oxide/interface/rutile model, where the roughness and interface are modeled using the incomplete Beta function. [ABSTRACT FROM AUTHOR]

From the first principles, in the framework of the density functional theory in LDA and LDA+U approximations, the band structure, total and partial densities of electronic states, spatial distribution of the electron charge density, also the optical functions: dielectric constant, refractive and absorption indices, reflection and absorption coefficients of Na2GeSe3 crystal have been calculated. According to the calculation results, Na2GeSe3 is a direct-gap crystal with the top of valence band and the bottom of conduction band at the point r of Brillouin zone. The calculated band gap is Egd = 1.7 eV LDA and Egd = 2.6 eV in the LDA+U approximations. Based on the data of total and partial densities of electronic states, contributions of atomic orbitals to the crystalline ones have been determined. Also, the data of chemical bond formation in the crystals under discussion have been obtained. [ABSTRACT FROM AUTHOR]

The spectral dependence of the transmittance as a function of the film thickness, the refractive index of the substrate, bandgap and the Cauchy parameters (α and β) of the semiconductor material was determined from condition of interference extremes. The absorption coefficient was simulated for the structure – thin film/substrate. Cadmium chalcogenides (CdTe, CdSe, and CdS) deposited on quartz substrates was selected as model samples. Experimental behavior of substrate transmittance was used to determine its refractive index. The theoretical results are compared with the experimental data and shows good agreement.

Optical functions and transitions are essential for a material to reveal the light–matter interactions and promote its applications. Here, we propose a quantitative strategy to systematically identify the critical point (CP) optical transitions of 2D semiconductors by combining the spectroscopic ellipsometry (SE) and DFT calculations. Optical functions and CPs are determined by SE, and connected to DFT band structure and projected density of states via equal-energy and equal-momentum lines. The combination of SE and DFT provides a powerful tool to investigate the CP optical transitions, including the transition energies and positions in Brillouin zone (BZ), and the involved energy bands and carries. As an example, the single-crystal monolayer WS2 is investigated by the proposed method. Results indicate that six excitonic-type CPs can be quantitatively distinguished in optical function of the monolayer WS2 over the spectral range of 245–1000 nm. These CPs are identified as direct optical transitions from three highest valence bands to three lowest conduction bands at high symmetry points in BZ contributed by electrons in S-3p and W-5d orbitals. Results and discussion on the monolayer WS2 demonstrate the effectiveness and advantages of the proposed method, which is general and can be easily extended to other materials.

Under varying hydrostatic pressures ranging from 0 to 150 GPa, first-principles calculations were conducted to investigate the structural, electronic, bonding, optical, elastic, and mechanical characteristics of the Lead (Pb)-free halide perovskite FrCaCl 3 using both the GGA and hybrid HSE06 parameterized density functional theory (DFT). Since the FrCaCl 3 cubic perovskite has not yet been synthesized experimentally, its structural and thermodynamic stabilities are confirmed by the Goldschmidt tolerance factor, the octahedral factor, and the formation energy. The induction of pressure has caused a simultaneous decrease in both the lattice parameters and the electronic band gap. Applying the hybrid HSE06 potential refines the accuracy of the band gap, with values decreasing from 5.705 to 2.618 eV from 0 to 150 GPa pressure, suggesting improved optoelectronic attributes. Employing pressure facilitates the formation of stronger chemical bonds characterized by reduced bond lengths. The investigation of optical functions demonstrates that with increased pressure ranging to 150 GPa, the optical conductivity along with the absorption coefficient is oriented towards the low-energy region. The FrCaCl 3 perovskite has the prospect to be used in X-ray imaging and other fields of nuclear medicine and diagnostics as it contains the radioactive element Francium (Fr). Additionally, it is found via the study of mechanical characteristics that FrCaCl 3 is mechanically stable under various applied pressure, and adding pressure makes it more ductile as well as more anisotropic., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

CdSe nanorods (NRs) are assembled using hydrothermal method using polyethylene glycol as a surfactant. The diameter and the length of the rods are found to be in the ranges of 10–30 and 80–210 nm, respectively. Besides, the CdSe NRs exhibit hexagonal structure with a crystallite size of 9.61 nm. Different concentration of CdSe NRs are mixed with poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). The structural features of the nanocomposites in the form of thin films prepared by spin-coating technique are studied by using of X-ray diffraction, field emission scanning microscope and atomic force microscope. The surface roughness of the MEH-PPV is calculated as 5.4 nm, which is significantly increased by the addition of CdSe NRs. Besides, the transmittance and the reflectance of the nanocomposite films are measured at the normal incidence of the light over wavelength range 200–2500 nm. The optical functions such as absorption coefficient and refractive index of the films are calculated and analyzed. The optical band gap of MEH–PPV is determined as 1.95 eV and is decreased with increasing CdSe NRs content. In addition, the single oscillator model is used to evaluate the optical oscillator parameters. Finally, the ratio of the free carriers to their effective mass is found to increase by increasing CdSe content. [ABSTRACT FROM AUTHOR]

We report the optical functions of diphenylsiloxane-dimethylsiloxane (DPS-DMS) copolymer as determined from reflection spectroscopic ellipsometry (SE) and transmission ultraviolet-visible data, which were generated over 191–1688 nm from a commercial sample of DPS-DMS. This material is a random, linear copolymer terminated with silanol groups that is a liquid at room temperature and pressure. Both reflection and transmission measurements required special experimental considerations. The reflection SE measurements utilized the "rough-surface" method, wherein the liquid was poured onto a roughened (frosted) glass slide, which scatters the reflected light leaving only the reflection from the liquid surface. That is, there is effectively no substrate or material beneath the liquid that affects the ellipsometry measurements or that needs to be modeled. Transmission measurements were obtained via a dual cuvette approach to eliminate the effects of the cuvettes. The reflection data provided the refractive index across the entire spectral range as well as the extinction coefficient at ultraviolet wavelengths. The transmission measurements provided input for the extinction coefficients at visible and near infrared wavelengths, where the liquid is transparent or semitransparent. The reflected SE data were modeled using a Sellmeier dispersion model and six Gaussian oscillators plus a surface roughness layer. This produced a good fit with a mean squared error (MSE) of 2.41. For example, we obtained the following n(λ) values, where λ is the wavelength in nanometers: n(300) = 1.534, n(500) = 1.477, and n(1000) = 1.458. As expected, the refractive index of DPS-DMS is higher than that of liquid polydimethylsiloxane. [ABSTRACT FROM AUTHOR]

II-VI binary semiconducting compounds belong to the cadmium chalcogenide family (CdS, CdSe, CdTe). They are promising materials for photovoltaic and sensor applications (in solar energetics, gases sensors). CdTe and CdSe are good photovoltaic materials due to their high absorption coefficient and nearly optimum bandgap energy for the efficient absorption of light and conversion into electrical energy. In particular, CdS is the most used material as an optical window in heterojunction solar cells based on CdTe and CIGS. CdSe thin films have a great potential for fabricating solar batteries of high efficiency, photoreceivers, light-emitting diodes, nanosensors, biomedical devices for image processing, thin film transistors, and other optoelectronic devices for solar hybrid systems. The results of experimental studies of the optical properties of CdSe thin film annealed in the atmosphere of CdCl2 are presented. The synthesis of CdSe thin film was carried out by the quasi close-space sublimation method on an ITO/glass substrate. The quality of the obtained film was studied using scanning electron microscopy and energy-dispersive X-ray analysis. Optical transmission and reflection spectra were obtained experimentally. Optical constants and the bandgap of the films under study have been determined (Eg= 1.67 eV). Optical properties (refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ) and dielectric functions ε(λ)) of CdSe thin films and thickness (d) can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. The single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated. [ABSTRACT FROM AUTHOR]

II-VI binary semiconducting compounds belong to the cadmium chalcogenide family (CdS, CdSe, CdTe). They are promising materials for photovoltaic and sensor applications (in solar energetics, gases sensors). CdTe and CdSe are good photovoltaic materials due to their high absorption coefficient and nearly optimum bandgap energy for the efficient absorption of light and conversion into electrical energy. In particular, CdS is the most used material as an optical window in heterojunction solar cells based on CdTe and CIGS. CdSe thin films have a great potential for fabricating solar batteries of high efficiency, photoreceivers, light-emitting diodes, nanosensors, biomedical devices for image processing, thin film transistors, and other optoelectronic devices for solar hybrid systems. The results of experimental studies of the optical properties of CdSe thin film annealed in the atmosphere of CdCl2 are presented. The synthesis of CdSe thin film was carried out by the quasi close-space sublimation method on an ITO/glass substrate. The quality of the obtained film was studied using scanning electron microscopy and energy-dispersive X-ray analysis. Optical transmission and reflection spectra were obtained experimentally. Optical constants and the bandgap of the films under study have been determined (Eg= 1.67 eV). Optical properties (refractive index n(λ), absorption coefficient α(λ), extinction coefficient k(λ) and dielectric functions ε(λ)) of CdSe thin films and thickness (d) can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. The single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated. [ABSTRACT FROM AUTHOR]

A theoretical study of the structural, elastic, electronic, optical, magnetic, and thermoelectric properties of the newly synthetized diamond-like quaternary semiconductor CuMn2InSe4 was carried out in this paper. The calculated equilibrium structural parameters are in excellent agreement with available experimental data. The single-crystal and polycrystalline elastic moduli were predicted using energy strain technique. Electronic properties, including band energy dispersion, total and projected densities of states, and charge distribution map, were calculated and analyzed. Total and local magnetic moments were determined. Linear optical functions were predicted from the calculated band structure. We studied the chemical potential dependence of the thermoelectric parameters, including Seebeck coefficient, electrical conductivity, thermal conductivity, and power factor. The maximum power factor and the corresponding chemical potential are estimated. The obtained results were compared with available ones. [ABSTRACT FROM AUTHOR]

The results of experimental and theoretical studies of the optical and energy properties of thin CdSe films obtained by the quasi-closed volume method are presented. The synthesis methodology and the results of structural and optical studies of thin CdSe films deposited on the surface of a quartz substrate of brand KV (GOST (State Standard) 15130-86) are given. The quality of the films is analyzed using the X-ray diffraction, energy dispersive analysis, and scanning electron microscopy techniques. Using the pseudopotential method, the dynamics of changes in the parameters of the electronic subsystem of a CdSe film is theoretically studied. The direct-gap nature of the energy gap of the film is established. Based on the density of states, the genesis of the conduction and valence bands is established. Using the Kramers–Kronig relations, we obtained the spectra of optical dielectric functions and the reflectance, refractive index, and extinction spectra, which satisfactorily correlate with the obtained experimental data. [ABSTRACT FROM AUTHOR]

Intending to advance the use of halide-perovskites in technological applications, in this research, we investigate the structural, electronic, optical, and mechanical behavior of metal-halide perovskites ACaCl 3 (A = Cs, Tl) through first-principle analysis and assess their potential applications. Due to the applied hydrostatic pressure, the interaction between constituent atoms increases, thereby causing the lattice parameter to decrease. The band structure reveals that band gap nature transits from indirect to direct at elevated pressure. Moreover, at high pressure, the electronic band structure shows a notable band gap contraction from the insulator (>5.0 eV) to the semiconductor region, which makes them promising for electronic applications. The charge density map explores the ionic and covalent characteristics of Cs/Tl-Cl and Ca-Cl under pressured and unpressurized environments. Induced pressure enhances the optical conductivity as well as the optical absorption that moves toward the low-energy region (red shift), making ACaCl 3 (A = Cs, Tl) advantageous for optoelectronic applications. Additionally, this study reveals that the mechanical properties of ductility and anisotropy were found to be improved at higher pressures than in ambient conditions. Overall, this study will shed light on the technological applications of lead-free halide perovskites in extreme pressure conditions., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

AMn 2 P 2 (A = Ca, Sr) materials are first-time investigation using ab-initio-based on Density Functional Theory (DFT). Different physical characteristics, including structural, thermal, electrical, mechanical, elastic anisotropic, and optical characteristics are investigated. We computed the crystal structure and lattice parameters, it demonstrates consistency with earlier experimental data. The calculated formation enthalpy and phonon calculation showed the thermodynamic and dynamical stability. Both AMn 2 P 2 (A = Ca, Sr) materials seem to be stable by the standards of Born criteria, brittle in nature, and elastically anisotropic. The investigated elastic moduli show good agreement with previously calculated data where available. Metallic nature of AMn 2 P 2 (A = Ca, Sr) materials has been confirmed from the band structure and DOS calculations. The optical properties such as dielectric constant, refractive index, absorption, conductivity, reflectivity, and loss function were also considered to predict optoelectronic besides photovoltaic devices. The very low minimum thermal conductivity ensured that CaMn 2 P 2 can be used as a better Thermal Barrier Coating (TBC) material than SrMn 2 P 2. • To investigate the structural, mechanical, electronic, optical, and thermodynamic properties of CaMn 2 P 2 and SrMn 2 P 2 compounds. • Investigated lattice parameters showed similar result with the theoretical and experimental data • The Poisson's ratio and Pugh's ratio revealed that all the compounds have ductile nature. The metallic nature of these phases was found from their band structure calculations. • Detailed investigation was also performed on optical propertiesSuch as the dielectric function, absorption, and conductivity. • The very lower values of minimum thermal conductivity and Debye temperature are indicative to their use as thermal barrier coating (TBC) material. [ABSTRACT FROM AUTHOR]

• Investigation of pressure-induced physical properties of K M Cl 3 (M = Ge, Sn). • Semiconductor to metallic transition occurred under pressure. • Enhanced optoelectronic performance under pressure. • Enhanced ductile and anisotropic nature under pressure. This article investigates the physical properties of lead-free tin- and germanium-based halide perovskites under pressure via the density functional theory to use as potential photovoltaic materials. Specifically, the structural, electronic, optical, and mechanical properties of K M Cl 3 (M = Ge, Sn) under diverse hydrostatic pressures ranging from 0 to 8 GPa are examined to vindicate the compounds' superiority for useful applications. The structures show high precision in terms of lattice constants, which approves the formerly published data. The calculated lattice constant (5.261 and 5.58 Å for KGeCl 3 and KGeCl 3 , respectively, at 0 GPa) and unit cell volume (145.67 and 173.80 Å3 for KGeCl 3 and KGeCl 3 , respectively, at 0 GPa) are significantly reduced ((lattice constant 4.924 Å (5.183 Å) and unit cell volume 119.41 Å3 (139.39 Å3) for KGeCl 3 (KSnCl 3) at 8 GPa) due to the pressure effect, while the cubic phase stability is maintained. Under ambient pressure, the calculated band gap reveals the compounds' semiconducting nature. Nevertheless, when pressure is increased, the band gap narrows, enhancing its conductivity and igniting its route towards semiconductor to metallic transition. The ionic and covalent bonding nature of K-Cl and Ge(Sn)-Cl, respectively; as well as the decrement of bond length due to external pressure are marked by charge density mapping. The optical functions are also enhanced when pressure is devoted, vindicating the chosen perovskites' suitability in various optoelectronic devices in the visible and ultraviolet ranges. Likewise, while maintaining mechanical stability, hydrostatic pressure significantly impacts mechanical properties. The ductility and anisotropic behavior of both perovskites are intensified under applied pressure. [ABSTRACT FROM AUTHOR]

The polarization dependences of reflection and wavelength modulated reflection spectra of quantum wells In 0.68 Al 0.1 Ga 0.13 As/In 0.42 Al 0.22 Ga 0.24 As were investigated. Spectral dependences of refractive indices, extinction coefficients, real and imaginary parts of dielectric constants of quantum wells structures for different polarizations were calculated by the Kramers–Kronig analysis. A phenomenon of birefringence and an interference of polarized light waves in quantum wells were researched. The isotropic wavelength λ 0 = 1.246 μm was found out. Interference spectra changes the density of fringes and refractive indices (Δ n i , Δ n KK = n Р,Р – n S,S ) intersect zero axis at energy of isotropic wavelength (0.955 eV). [ABSTRACT FROM AUTHOR]

We have investigated theoretical Vickers hardness, thermodynamic and optical properties of four zirconium metal-based MAX phases Zr2AC (A = Al, Si, P and S) for the first time in addition to revisiting the structural, elastic and electronic properties. First-principles calculations are employed based on density functional theory (DFT) by means of the plane-wave pseudopotential method. The theoretical Vickers hardness has been estimated via the calculation of Mulliken bond populations and electronic density of states. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats and volume thermal expansion coefficient of all the compounds are derived from the quasi-harmonic Debye model. Further, the optical properties, e.g., dielectric functions, indices of refraction, absorption, energy loss function, reflectivity and optical conductivity of the nanolaminates have been calculated. The results are compared with available experiments and their various implications are discussed in detail. We have also shed light on the effect of different properties of Zr2AC as the A-group atom moves from Al to S across the periodic table. [ABSTRACT FROM AUTHOR]

• Pressure impact is used for the first time on cubic halide perovskite CsCaBr 3. • The lattice parameters decreased under pressure as the interatomic distance is reduced. • The transition of band gap nature from indirect to direct is occurred at 40 GPa. • As the pressure rises, the optical spectra shift toward lower energy. • According to the mechanical stability criteria, CsCaBr 3 is stable over the whole range of applied pressure (0–80) GPa. • Pressure makes the CsCaBr 3 compound more ductile and anisotropic. Throughout this study, the effects of hydrostatic pressure on the physical properties of halide perovskite CsCaBr 3 are explored using the density functional theory. The calculated lattice parameters nicely agree with the previous experimental and theoretical reports, but being decreased under pressure as the interatomic distance is reduced. The electronic band gap is significantly reduced from ultra-violet to visible region under pressure, which makes easier to transport electron from valance band to conduction band responsible for enhancing photovoltaic device efficiency. In addition, the transition of band gap nature from indirect to direct is occurred at 40 GPa, which is more suitable for a material to be used in optoelectronic applications. Deep optical analysis suggests the potential applications of titled perovskite in microelectronics, integrated circuits, QLED, OLED, solar cell, waveguides, solar heat reducing materials, and surgical instruments. The elastic constants nicely pursue the Born stability conditions confirming the mechanical stability of CsCaBr 3 under entire range of applied pressure, which justify the thermodynamic stability obtained by the negative values of formation enthalpy. The mechanical properties are also significantly affected by external pressure, which make this compound more ductile and anisotropic. [ABSTRACT FROM AUTHOR]

Throughout this study the density functional theory has been employed to investigate the structural, electronic, optical, and mechanical properties of cubic halide perovskite CsYbCl 3 under different hydrostatic pressure ranging from 0 to 200 GPa. The lattice constant and unit cell volume are significantly reduced due to pressure effect. The reducing tendency of band gap is also observed under pressure up to 120 GPa, but the transformation of semiconducting to metallic behavior is found for 160 and 200 GPa pressure. The tuning of band gap is responsible for enhancing the electron transfer from valence band to conduction band, which increases the optical absorption and conductivity making the compound more advantageous for device applications. The analysis of optical functions reveals that the hydrostatic pressure makes the titled compound even more suitable for various potential applications. The mechanical properties reflect the ductile and anisotropic nature of CsYbCl 3 , on which the applied pressure manifest substantial impact. • Detailed investigation on the physical properties of cubic halide perovskite CsYbCl 3 under pressure. • The calculated lattice parameters nicely agree with the previous experimental and theoretical work. • Semiconducting to metallic transition of CsYbCl 3 occurred at 160 GPa. • Deep optical insights suggest the potential optoelectronic applications of CsYbCl 3 under pressure. • Ductility and anisotropy increase under pressure. [ABSTRACT FROM AUTHOR]

Abstract: -5-Sulfono-7-(4-x phenyl azo)-8-hydroxy quinoline (SAHQ)-x ligands, x = NO2 or CH3 or Cl have polycrystalline structure in as synthesized condition. Thermally evaporated thin films of SAHQ-x have crystal structure depending on the substitution group; SAHQ-NO2 and SAHQ-Cl films have nano-crystalline structure with different degree of crystallinity and SAHQ-CH3 film has amorphous structure. The changes in optical functions and therefore optical constants with substitution group variation have been calculated by using spectrophotometer measurements of the transmittance and reflectance at nearly normal incidence of light in the wavelength range 200–2500 nm. Substitution group variation influences the refractive index, dispersion parameters, optical functions and bond length of SAHQ. It has no influence on mobility, relaxation time and plasma frequency of charge carriers. The obtained optical energy gaps for SAHQ-x ligands, x = NO2 or CH3 or Cl are 1.89, 2 and 2eV, respectively. [Copyright &y& Elsevier]

Abstract: Complex refractive indices N = n +ik for a-cut Sr x Ba1−x Nb2O6 single crystals with four nominal values of composition x =0.40; 0.50; 0.61; 0.75 were studied by spectroscopic ellipsometry in the photon energy range 2–5eV of crystal transparency and fundamental electronic absorption. The ellipsometric data were evaluated taking into account an uniaxial anisotropy and an unintentional surface roughness. We use a global composition dependent Sellmeier fit as a reference for monitoring the crystals composition. The optical model yields indirect and direct optical band gap energies E g in the spectral range 3.77–4.03eV and 4.28–4.55eV, respectively, depending on the Sr/(Ba+Sr) content ratio x and light polarization. The congruently melting composition Sr0.61Ba0.39Nb2O6 shows distinct dispersion features in the imaginary part of the UV complex refractive index with respect to other compositions. [Copyright &y& Elsevier]

Abstract: The transparency, reflection and luminescence spectra of In0.3Ga0.7As structures with 8nm thickness and quantum wells limited by the barrier layer GaAs of a 9nm (upper layer) and 100nm (bottom layer) thickness had been studied in the region of photon energy 0.5–1.6eV. Lines associated with the transitions hh,lh1-e1(1s,2s,3s), hh2,lh2-e2(1s,2s,3s), hh1,lh1-e2(1s) and hh3,lh3-e3(1s) had been revealed in reflection spectra. The shapes of the reflection and transparency lines had been calculated using a single oscillator model of dispersion relations and the Kramers–Kronig integrals. The binding energy of hh,lh1-e1 excitons, the effective mass mhh ∗ and mlh ∗ and the damping factor for the optical transitions to QW and QD had been determined. The lifetime of charge carriers on quantum dots varies in the range of 0.04–0.1ps, while the radiative lifetime of excitons in quantum wells in the considered structure is around 2ps. [Copyright &y& Elsevier]

Abstract: The electronic and optical functions of zinc-blende III-phosphide (BP, AlP, GaP and InP) are studied based on the first-principles calculations. The optical functions, including the complex dielectric function, optical reflectivity, refractive index, extinction coefficient, absorption efficient and electron energy loss, are discussed for radiation up to 36eV by analyzing the energy band structures and density of states calculated. The common trends and the differences among the four III-phosphide compounds are presented. We also have explained the origin of the spectral peaks on the basis of the electronic band structures. Calculated optical functions indicate that these zinc-blende III-phosphide can serve as shielding devices for ultraviolet radiation. Our results of the electronic and optical properties are in agreement with the experimental data when available, in other case they can be considered as predictions. [ABSTRACT FROM AUTHOR]