Direct Gap Research Articles

Halide Mixing in Cs2AgBi(I x Br1-x )6 Double Perovskites: A Pathway to Tunable Excitonic Properties.

Cs2AgBiBr6 is an emerging double perovskite semiconductor with robust stability. However, its potential for photovoltaics is limited by its indirect band gap and localized electronic structure featuring a resonant exciton with a large binding energy. Cs2AgBi(I x Br1-x )6 nanocrystals with iodide concentrations of up to 100% were recently demonstrated, but an atomistic understanding of how halide mixing affects the electronic and excited-state structure is missing. Here, we use first-principles GW and Bethe-Salpeter Equation calculations to show that halide mixing leads to a pronounced change in the band gap and character of optical excitations. Exciton binding energies are reduced by up to a factor of 5, with significantly more delocalized excitons in I-rich compounds. We further show that phase-pure bulk alloys with x ≤ 0.11 can be fabricated using mechanosynthesis and measure a red-shifted absorption in line with our calculations. Our study highlights that halide mixing in double perovskites can not only lead to significant band gap changes but may also be used for tuning excitonic properties.

Design and characterization of borosilicate glass modified with TiO2 for enhanced optical and radiation shielding applications

This work investigates the potential of borosilicate glass doped with titanium dioxide (TiO2) for radiation shielding applications. The study explored the impact of varying TiO2 concentrations on the glass structure, optical properties, and radiation shielding effectiveness. X-ray diffraction (XRD) and Raman spectroscopy confirmed the amorphous nature of the glasses. The addition of TiO2 affected the glass network structure, as evidenced by changes in the Raman spectra and density measurements. UV–Vis spectroscopy revealed a red shift in the absorption edge (416–481 nm) and a decrease in the indirect optical band gap (2.91–2.70 eV) with increasing TiO2 content. The refractive index also increased from 2.54 to 3.54 with TiO2 concentration. The mass attenuation coefficient (MAC) and linear attenuation coefficient (LAC) increased significantly with TiO2 addition, indicating enhanced radiation attenuation capability. The inclusion of TiO2 reduced the half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP), while increasing the effective atomic number (Zeff). The effective electron density (Neff) and effective conductivity (Ceff) showed a slight increase with TiO2 content. Energy build-up factors (EBF and EABF) indicated a higher rate of radiation intensity increase and energy absorption within the glass due to the presence of TiO2. Finally, the incorporation of TiO2 into borosilicate glass offered a promising approach to developing improved optical and radiation shielding glasses.

Properties of bismuth based Bi2A3 (A = S, Se, Te) chalcogenides for optoelectronic and thermoelectric applications

Structural, electronic, optical, mechanical, thermoelectric and dielectric properties of binary Bi2A3 (A = S, Se, Te) chalcogenide semiconductors are studied by first-principles approach. Bismuth sulfide (Bi2S3) is found to be structurally stable in orthorhombic structure while bismuth selenide (Bi2Se3) and bismuth telluride (Bi2Te3) are stable in trigonal structure. Calculated mechanical properties reveal that all three Bi2A3 (A = S, Se, Te) compounds fulfil the mechanical stability criteria. Band structure calculations reveal that the Bi2S3 exhibits direct optical band gap (Eg = 1. 58 eV) which lies in the near-infrared (NIR) region, while the calculated Eg of Bi2Se3 and Bi2Te3 are found to be 0.53 eV and 0.35 eV, respectively lying in the far-infrared region. For Bi2S3 and Bi2Se3 compounds, the calculated dielectric properties show strong anisotropic behavior, while negligible anisotropic dielectric behavior is observed for Bi2Te3. Calculated optical properties show that all three Bi2A3 compounds possess high absorption coefficient (> 104 cm−1). For all three Bi2A3 (A = S, Se, Te) compounds, the calculated optical conductivity show prominent peak corresponding to the occurrence of optical conduction at energies 3.36 eV, 2.65 eV and 2.02 eV respectively. Calculated optical results support the results deduced from band structures and density of states spectra. Optical properties and dielectric behavior suggest that the Bi2S3 compound has suitable band gap and has potential to use for photovoltaic applications while Bi2A3 (A = Se, Te) compounds could be used in infrared detectors and other optical devices. Calculated thermal properties reveal that the Bi2A3 (A = S, Se, Te) chalcogenides could be potential materials for thermoelectric applications.

PVA/CMC/PEG blended polymer loaded with ZnCo1.9Al0.1O4/carbon nanoparticles/PANi as a promising films for UV radiation shielding

Polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and polyethylene glycol (PEG) have been employed as polymeric matrices for the synthesis of polymeric nanocomposite films that incorporate ZnCo1.9Al0.1O4, carbon nanoparticles (CNPs) and polyaniline (PANI) as fillers. X-ray diffraction technique was utilized to examine the structure of ZnCo1.9Al0.1O4 filler and the formed PVA/CMC/PEG/ZnCo1.9Al0.1O4/CNPs/x wt % PANi blends. The morphology of the doped blend was explored using the scanning electron microscopy technique. The increases in absorbance, especially in the UV spectrum, demonstrate the potential of these blends in UV-blocking and UV-filtering applications. The minimum direct and direct optical energy gaps are 5.62 and 4.77 eV obtained as the quantity of PANi became 0.3 wt %. The highest refractive index values (n = 1.66 at 600 nm) were acquired as the blend was doped with 0.4 wt % PANi. The impact of different fillers on the linear and nonlinear optical parameters was explored. The inclusion of ZnCo1.9Al0.1O4/CNPs/x wt % PANi resulted in an improvement in PVA/CMC/PEG blended polymer's optical conductivity. The FL intensities of the loaded blends are comparatively lower than those of the undoped blend. The values of the dielectric constants of doped blends with x = 0 or 0.4 are notably higher than those of other blends. Doped blend with x = 0.2 exhibited the highest energy density value (9 × 10−3 J/m3 at 1 kHz). The doped blend with x = 0.4 has the highest ac conductivity (1.53 × 10−8 Sm−1 at 1 kHz). The influence of doping on the relaxation time and capacitance behavior of the host blend was inspected. These outcomes suggest the opportunity of employing the created nanocomposites in capacitive energy storage and optoelectronic devices.

K2HgGe3Se8: A Quaternary Hg-Based Selenide with Nonlinear Optical Properties.

A new quaternary Hg-based selenide K2HgGe3Se8 was successfully synthesized and characterized as an engaging infrared (IR) nonlinear optical (NLO) material, which crystallizes in the P21 space group of the noncentrosymmetric monoclinic crystal system. The crystal structure of K2HgGe3Se8 is characterized by the stacking of countless layers with K+ cations filling the interlayers. The UV-vis-NIR diffuse reflectance spectrum shows that K2HgGe3Se8 possesses an indirect band gap of 2.13 eV. The second harmonic generation (SHG) response of K2HgGe3Se8 is approximately 1.1 times that of AgGaS2 (AGS) within the particle size of 20-50 μm along with a nonphase-matching (NPM) behavior at 2090 nm, as indicated by the SHG test. K2HgGe3Se8 also has a large powder laser-induced damage threshold (∼ 2.3 × AGS). As revealed by theoretical calculations, the optical properties of K2HgGe3Se8 are predominantly determined by [HgSe4] and [GeSe4] tetrahedra, and K2HgGe3Se8 possesses a calculated optical band gap of 1.44 eV together with a maximum SHG coefficient d22 of -7.70 pm V-1.

The pH-dependent properties of cuprous oxide thin films prepared by electrochemical deposition for liquid petroleum gas sensing

Efficient liquid petroleum gas sensing was investigated by modulating the pH level (8, 9, 10, 11, and 12) of electrochemically deposited nanostructured cuprous oxide thin films in a lactate bath. The synthesized films were characterized by surface contact angle, XRD, SEM, UV–Vis absorption, Mott-Schottky, and AC impedance spectroscopy measurements. These displayed a unique initial increment or decrease followed by a persistent decrement or increment at pH 9–10. This turning pH point exhibited the least wetting polycrystalline Cu2O growth with the smallest crystallite size of ∼ 45 nm, the highest dislocation density of ∼50 µm−2, and a strain of 0.03 according to X-ray diffraction. SEM micrographs identified ∼ 1 µm-sized, closely structured grains with trigonal-prismatic shapes. The Mott-Schottky plots drawn from C-V measurements revealed a significant dependence of flat band potential and free carrier density on the deposition bath pH level. Cu2O films deposited using the lactate bath changed the conductivity at pH 9 from n-type to p-type when increasing the pH value. With the conductivity transition, films prepared at pH 9 displayed a relatively high direct band gap energy of 2.28 eV. Liquid petroleum gas (LPG) sensing at 70 °C demonstrated the most substantial gas response of 11.5 % at pH 10 Cu2O films. Cu2O thin films deposited at pH 9 emerged as the most stable and reproducible p-Cu2O LPG sensor, with response and recovery times ranging from 20 to 25 seconds. Remarkable changes in the film structures and morphologies were revealed with pH values above 9 after the gas exposure. The grain shape and distribution of pH 9 remained unchanged, assuring the stability of the sensing platform.

Continuous-Flow Synthesis of Zn1-xMnxS Nanoparticles at Ambient Conditions.

With its large direct band gap and good chemical stability, ZnS is suitable for many applications, including light-emitting diodes, panel displays, and photodetection. Here, nanoparticles of ZnS are synthesized phase pure under ambient conditions by precipitation in a simple and scalable continuous-flow reactor. Furthermore, different degrees of Zn substitution with Mn have been investigated, Zn1-xMnxS, with x = 0.05, 0.19, and 0.25 according to X-ray fluorescence measurements. The products are analyzed with multitemperature synchrotron powder X-ray diffraction (PXRD) and X-ray total scattering. The analysis reveals phase-pure synthesis products with the sphalerite structure and crystallite sizes in the range of 3.8-4.7 nm in agreement with scanning transmission electron microscopy. Only Zn0.75Mn0.25S shows traces of Mn3O4, indicating that x = 0.25 is above the substitution limit as the impurity appears. Substitution of Zn with Mn in the nanoparticles is confirmed by energy-dispersive X-ray spectroscopy, as well as an observed decrease in the band gap, decrease in the sphalerite-to-wurtzite phase transition temperature, and increase in the unit cell dimensions with increasing Mn content. Based on the modeling of the PXRD Rietveld refined atomic displacement parameters, the Debye temperature for ZnS and Zn0.95Mn0.05S is determined to be 322 ± 13 and 394 ± 22 K, respectively.

Indirect to direct band gap engineering of cubic bromide perovskite AlMgBr3 under pressure: First-principles calculations for enhanced optoelectronic applications

Through first principles, the structural, electronic, optical, mechanical, and thermodynamic properties of AlMgBr3 at different pressures are investigated for the first time. At 0 GPa, cubic AlMgBr3 is an indirect band gap insulator (Eg = 3.958 eV). Interestingly, its band gap type changes from an indirect band gap to a direct band gap at 5 GPa, making it a more favorable material for optoelectronic device applications. In addition, as the pressure increases, the conduction band electrons move downward, resulting in a reduction of the band gap, and the band gap transition from the ultraviolet to visible region. The optical properties show that AlMgBr3 has a high dielectric constant, refractive index, and conductivity, which is favorable for its application in solar cells, waveguides and other optoelectronic devices. The phase transition point of AlMgBr3 was determined to be 39.6 GPa based on the mechanical stability conditions, and the mechanical properties revealed the ductility, anisotropy and machinability of AlMgBr3. By using the quasi-harmonic Debye model, the effect of temperature and pressure on the bulk modulus, coefficient of thermal expansion, isobaric heat capacity, Debye temperature, and entropy were also calculated. It is worth mentioning that the electronic, optical, mechanical and thermodynamic properties of AlMgBr3 have been significantly enhanced under pressure.

A theoretical analysis of the effect of hydrostatic pressure on cerium oxide for renewable energy applications

The characteristics of cubic cerium oxide (CeO2) have been investigated using density functional theory (DFT) using the PBE-GGA exchange–correlation functional. This study mainly focused on the structural, elastic, and optoelectronic properties of the CeO2 under the application of external hydrostatic pressure. It is observed that lattice constants and volume tend to decrease with increasing pressure. Based on the observed trends in lattice constants variations, CeO2 exhibits compressibility at high-pressure conditions, although it remains structurally unchanged throughout the pressure range of 0 to 100 GPa. Applying pressure within the range of 0 to 100 GPa reveals a distinct characteristic associated with the emergence of electronic bandgap opening. The material displays an indirect energy bandgap, with its magnitude increasing from 2.659 eV to 4.055 eV under rising pressure. To deeply understand the impact of external pressure on the optical behaviour of CeO2, extensive investigation has been conducted on several optical parameters such as the dielectric function, refractive index, optical reflectivity, absorption coefficient, optical conductivity, and loss function throughout the energy range up to 50 eV. However, there is a tendency for optical parameters to show sharpening peaks that shift somewhat towards higher energies. Furthermore, we have also tested the impact of bandgap modulation induced in CeO2 by proposing a CsSnBr3-based solar cell with the One-Dimensional Solar Cell Capacitance Simulator software. Based on our findings, the use of cubic cerium oxide may find its potential to enhance the performance of optoelectronic and renewable energy devices.

DFT study of the electronic, optical and elastic properties of Cu2-xAgxMgSnS4 (x=0, 0.5, 1, 1.5, 2) alloys using TB-mBJ+U potential

In this study, we have conducted first-principles computations on the promising photovoltaic materials Cu2-xAgxMgSnS4 (x = 0, 0.5, 1, 1.5, 2). To determine the electronic characteristics of Cu2-xAgxMgSnS4(x = 0, 0.5, 1, 1.5, 2) in kesterite and stannite phases, we have used the Wien2k code based on density functional theory with the generalised gradient approximation (GGA) and modified Becke-Johnson (TB-mBJ) exchange potential. The results obtained by TB-mBJ likewise fall short of the experimental findings, like GGA and LDA. To get a comparable bandgap value with the experimental results, we have employed the TB-mBJ potential coupled with the Hubbard U correction (TB-mBJ + U), resulting in a more accurate representation of the pd hybridization. Electronic structure calculation reveals Cu2-xAgxMgSnS4(x = 0, 0.5, 1, 1.5, 2) materials as direct bandgap semiconductors, with band gaps ranging from 1.477 eV to 2.38 eV. The computed elastic constants confirm the mechanical stability of all materials. Additionally, we explored optical properties essential for their potential as absorber layers in photovoltaic applications, such as the imaginary and real components of the dielectric function, absorption coefficient, refractive index, reflectivity, and extinction coefficient. These predicted parameters provide valuable insights for researchers, facilitating further investigations into the photovoltaic potential of Cu2-xAgxMgSnS4 materials.

Comprehensive analysis of structural, mechanical, optoelectronic, and thermodynamic properties of Ba2XBiO6 (X = Y, La) double perovskites using density functional theory

The structural, mechanical, optoelectronic, and thermodynamic properties of Ba2XBiO6 (X = Y, La) double perovskites are critically analyzed using density functional theory. The Birch-Murnaghan equation of state confirms their structural stability, supported by tolerance factor analysis. For Ba2YBiO6 and Ba2LaBiO6, negative formation energies are −0.935 eV for Ba2YBiO6 and −0.836 eV for Ba2LaBiO6, confirming thermodynamic stability. Phonon dispersion curves indicate stable lattice vibrations, reducing the likelihood of spontaneous structural changes or phase transitions. Ba2YBiO6 possesses higher elastic constants C 11 = 222 GPa shows stiffness and exhibits brittle mechanical behavior, whereas the Pugh ratio and C 11 = 217 GPa for Ba2LaBiO6 shows ductility. The Poisson ratio classifies Ba2YBiO6 as a non-central force crystal and Ba2LaBiO6 as a central force crystal. Both materials are indirect band gap semiconductors, with band gap values of 0.75 eV for Ba2YBiO6 and 2.05 eV for Ba2LaBiO6. Optical properties suggest applications in UV and visible light-based optoelectronic devices. Thermodynamic properties, such as Debye temperature and heat capacity, support the idea that these materials are suitable for high mechanical applications. These findings provide insights for designing high-performance optoelectronic and mechanical devices.

Structural, electronic, optical, and thermoelectric features of Rb2XSbX’6 (X= Ag, Cu; X’= Cl, Br): Ab-initio calculations

This study investigates the electronic, optical, and thermoelectric properties of lead-free double halide perovskite materials, Rb2XSbX'6, through first-principles calculations employing Density Functional Theory (DFT) and the Wien2k code, complemented by Boltzmann transport theory. By substituting X with Ag or Cu and X’ with Cl or Br in Rb2XSbX’6, we uncover interesting properties. Rb2AgSbBr6, Rb2AgSbCl6, Rb2CuSbCl6, and Rb2CuSbBr6 exhibit low indirect band gaps of 1.18 eV, 2.17 eV, 1.22 eV, and 0.87 eV, respectively, alongside high absorption in the visible region. The studied compounds sustained a high level of structural and thermodynamic stability, which was confirmed by their high bulk modulus and negative formation energy. Furthermore, extensive values were observed for the figure of merit in the thermoelectric study. Given the strong agreement with previous research, these findings position the investigated materials as promising candidates for visible-light solar cell device applications.

Investigating the physicochemical, optical and microstructural properties of sodium doped CdO nano powders fabricated by co-precipitation technique for blue emission and antimicrobial applications

A series of cubic structured pristine and sodium doped CdO nanoparticles (Cd1-xNaxO NPs) with varying dopant concentrations have been synthesized using simple Co-precipitation process. Crystal structure and the connection between various structural parameters are evidenced using powder XRD diffractograms. The crystallite size is evaluated with different models and the mean crystallite size was reduced with Na ions doping concentration due to severe lattice distortion. The existence of various vibrational modes and functional groups were demonstrated through FTIR characterization. The signature of Cd–O and Na–O stretching modes were confirmed with FTIR. Raman spectra also confirmed the formation of metal–oxygen bond and the second order vibration features. The direct bandgap of the CdO material increased from 2.132 to 2.40 eV with an increase in the Na dopant content which presents the appearance of a blue shift as probed through UV–Vis spectroscopy. The surface morphology and microstructure of the samples were studied using FESEM and HRTEM images, respectively. EDAX measurements revealed the presence of Cd, and O in the host lattice and Cd, O and Na in the doped CdO constructions. The SAED concentric ring pattern of Cd1-xNaxO nanoparticles demonstrated the polycrystalline nature of the samples. PL study revealed the impression of intrinsic defects and the photoluminescence colour emission of the Cd1-xNaxO materials shifted more towards bright blue region as the Na doping concentration increased. CIE color coordinates of Na-doped CdO NPs shows intense bluish color and extending its applications in commercial UV lighting, blue LEDs and Fluorescent biological labelling and tagging. Cd1-xNaxO nanoparticles exhibited enhanced antibacterial activity with increasing Na doping content towards gram-positive, and gram-negative bacteria. Further, the antifungal analysis against C. albicans, and A. niger authenticate that Na+ substituted CdO nanoparticles shows excellent antifungal activity. The mechanism of the above observed results is examined in detail in this article.

Oxygen vacancy modulated optical and dielectric properties of photoactive γ-Fe2WO6

Ferrite compounds have gained scientific attention for their multifunctional attributes. This investigation explores the structural, optical, dielectric and conductivity properties of polycrystalline γ-Fe2WO6 synthesized by the solid state route. The X-ray diffraction confirmed the orthorhombic structure and single-phase formation, while the electron microscopy showed uniform distribution of dense micrometer-sized grains in γ-Fe2WO6. The FTIR spectroscopy analysis validated the presence of active stretching and bending modes, signifying oxygen anion vibration at both Fe and W sites. The simultaneous presence of Fe2+ and Fe3+ ions in the matrix, as confirmed by X-ray photoelectron spectroscopy (XPS), results in an augmented optical energy band gap and contributes to dielectric permittivity due to the charge carrier hopping mechanism between the trap sites. The compound manifests semiconductor attributes, evident in its indirect optical band gap measuring 1.7 eV. It is observed that the compound has effectively degraded the Methylene Blue (MB) under the visible light within 40 min with a degradation efficiency up to 63 %. The material's electrical conductivity, follows the Jonscher's power law, signifies its semiconductor nature and adheres to the Small Polaron tunneling model for charge conduction between neighboring sites. The impedance (Z′) curves exhibit dielectric relaxation (≤ 10 kHz) with a similar activation energy to the dc conductivity study. The activation energy, determined from both the impedance and conductivity analyses, indicates a connection with the migration of oxygen vacancies within the material. Our observation reveals the presence of oxygen vacancies, which possibly act as in-gap electron traps, enhancing the correlated optical and ac conductivity properties, making it an appealing material for diverse multifunctional applications.

Synthesis, Structural, and Optical Properties of Modified Poly(vinyl Chloride) Thin Films by Ethylenediamine Loaded with Metal Oxide Nanoparticles

AbstractPoly (vinyl chloride) (PVC) films modified with ethylenediamine (en) and doped by nanoparticles (TiO2, ZnO, NiO, and MgO). A mixture of 0.5 g PVC/en dissolved in THF and 0.01 wt % of nanoparticles were used in doping PVC to produce the nanocomposite films. All modified PVC films were characterized by different analysis techniques such as Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance Spectrometer (NMR), diffusive reflectance spectroscopy (DRS), X‐ray diffraction analysis (XRD), and scanning electron microscopy (SEM). The DRS was used to analyse the scattered IR energy of the samples at wavelengths between (250–1350 nm). The optical properties and oscillator strength were also studied, the transmittance and reflectance values declined for the PVC films, and the absorption coefficient was observed between (79–89 %). The direct energy gap decreased from 4.6 to 1.9, and the indirect energy gap reduced from 4.3 to 1.9. The XRD exhibited a semi‐crystalline structure and the SEM test exhibited a porous structure of all samples. The Urbach energy was increased from 0.8772 eV to 14.712 eV, single oscillator energy ( ) was also increased from 6.38 eV to 13.69 eV and the dispersion energy increased from 23.40 eV to 70.63 eV. Moreover, the surface roughness parameters Ra and Rq of the PVC films in modified and doping were increased from 3.86 nm to 8.14 nm, and 5.08 nm to 10.10 nm respectively. So, PVC results show increased optical properties after modification with en and doping by NPs are used in the light conversion and aerospace industries.

Synergistic effects of vacancy and doping at Ge sublattices on the electronic and magnetic properties of new Janus Ge2PAs monolayer

Recently, 2D materials based on IV-V group have attracted great attention because of their interesting physical properties. In this work, Janus Ge2PAs monolayer with good stability is predicted using first-principles calculations. Our simulations assert its non-magnetic semiconductor nature with an indirect band gap of 1.11(1.75)eV obtained by PBE(HSE06)-based calculations. Further, vacancy defects and doping with transition metals (TMs = Cr and Mn) are explored in order to induce novel physical aspects. It is found significant magnetization of Janus Ge2PAs monolayer induced by Ge vacancies with total magnetic moments between 1.58 and 1.97 μB, where magnetism is produced mainly by atomic species around the defect sites. Herein, single Ge vacancy metalizes the monolayer, while the half-metallicity is obtained by creating a pair Ge vacancies. Regardless doping site, feature-rich diluted magnetic semiconductor and half-metallic behaviors are also obtained in Janus Ge2PAs monolayer by doping with Cr and Mn atom, respectively. In these case, TM impurities originate mainly the system magnetism with total magnetic moments between 2.00 and 3.03 μB. In addition, the coexistence of Ge vacancy and doping is also investigated. The calculated spin density shows an antiparallel spin orientation of Cr dopant and its neighboring atoms, meanwhile a parallel spin orientation is observed for Mn impurity and its neighboring atoms. Consequently, small total magnetic moment of 0.53 μB is obtained by the synergistic effects of doping with Cr and Ge vacancy, meanwhile the coexistence of Mn dopant and Ge vacancy generates a larger value of 4.88/4.89 μB. In all cases, the origin of electronic and magnetic properties is unraveled. Our results introduce new prospective spintronic 2D materials made from a new Janus Ge2PAs monolayer.

First-principle study of the ground-state crystal structure and optoelectronic response of CsPbX3 (X= Cl, Br, I) for photovoltaic applications

The optoelectronic response and ground state crystal structure of tetragonal (P4/mbm), orthorhombic (Pmnb) and monoclinic (P21/m) phases of CsPbX3 (X = Cl, Br, I) are studied for optoelectronic applications using first principle simulations. Electric field gradient (EFG) and magnetic hyperfine interactions are investigated to explore the charge distributions surrounding the nucleus and local magnetic environment of the atomic nucleus. The orthorhombic phase of these compounds is more stable having lowest ground-state energy compared to tetragonal and monoclinic phases. The understudied halide perovskites have direct band gap nature and spin orbit coupling (SOC) effect splits Pb-p and X-p orbitals at the edges of conduction and valence band (CB and VB) respectively. At the edge of VB, the strongly hybridized X-p and Pb-p orbital and direct band gap nature of CsPbX3 is excellent for the light absorption and photovoltaic (PV) applications. The n-i-p configuration (FTO/ETL/CsPbX3/HTL/Au) of the simulated structure shows that CsPbI3 has improved power conversion efficiency (PCE) of 22.48 % and 22.32 % and quantum efficiency (QE) about ∼80 % in tetragonal and monoclinic phases respectively. The Pb and Cs values of EFG tensor in z-direction (Vzz) are close to each other, which show that the distribution of electronic charge density is similar near these nuclei. Moreover, Cs-s orbital has negligible contribution and Pb-p and I-p orbitals have higher contribution in the hyperfine field (HFF). The negative HFF indicates the opposite HFF contribution.

Tuning the optoelectronic properties of graphene monoxide by electric field, strain and heterostructure with Cd[formula omitted] ([formula omitted]=S, Se or Te)

Hydrogen production via photocatalytic water splitting has become a promising technique for developing clean and sustainable energy system. Low-dimensional carbon-based materials are under focus to develop high efficiency visible-light photocatalysts. Among the various 2D graphene-based materials, graphene oxides (GO) attracted attention in recent years. Recently identified GO such as graphene monoxide (GMO) shows promising electronic structure characteristics such as direct band gap behavior, high optical absorption, and well-dispersed band edges to use them in higher efficiency optoelectronic applications. Nevertheless, its valence band edge is distant from the water oxidation potential, and band gap value exceeds the ideal band gap required to effectively harvest solar energy, which minimizes its practical application in photocatalytic water splitting. Here, using hybrid density functional theory calculations, we are exploring the effect of applied electric field/strain on the photocatalytic water splitting and photovoltaic properties of GMO. We found that even after applying an electric field or strain, GMO retains the desirable direct band gap behavior, well-dispersed bands at the band edges, and high optical absorption in the visible range. Further, the band alignment analysis suggests that the application of compressive strain enhances the efficiency of photocatalytic water splitting by straddling the band edges with water redox potentials. Additionally, we explored the optoelectronic properties of GMO by designing its heterostructure with CdS, CdSe, and CdTe monolayers. Remarkably, the studied heterostructures demonstrated superior optical absorption in the visible spectrum and a low recombination rate of charge carriers by separating them across different layers with type-II band alignment; suggesting that these heterostructures will be efficient candidates for visible energy photocatalytic water splitting and higher-efficiency solar cells.

Photon Momentum Enabled Light Absorption in Silicon.

Photons do not carry sufficient momentum to induce indirect optical transitions in semiconducting materials, such as silicon, necessitating the assistance of lattice phonons to conserve momentum. Compared to direct bandgap semiconductors, this renders silicon a less attractive material for a wide variety of optoelectronic applications. In this work, we introduce an alternative strategy to fulfill the momentum-matching requirement in indirect optical transitions. We demonstrate that when confined to scales below ∼3 nm, photons acquire sufficient momentum to allow electronic transitions at the band edge of Si without the assistance of a phonon. Confined photons allow simultaneous energy and momentum conservation in two-body photon-electron scattering; in effect, converting silicon into a direct bandgap semiconductor. We show that this less-explored concept of light-matter interaction leads to a marked increase in the absorptivity of Si from the UV to the near-IR. The strategy provides opportunities for more efficient use of indirect semiconductors in photovoltaics, energy conversion, light detection, and emission.

Exploring the potential of bismuth-containing silicate borate glasses for optoelectronic devices and radiation protection

This study studied novel bismuth silicate borate glasses with different bismuth oxide (Bi2O3) concentrations for their optical and γ-radiation shielding capabilities. The glass samples were characterized using UV–Vis–NIR spectroscopy to determine their optical properties, including the optical absorption spectra, absorption edge, and optical band gaps. The FLUKA algorithm was used to determine the radiation shielding parameters in the energy range of 0.01–15 MeV. The results revealed that the optical absorption edge and intensity were influenced by the Bi2O3 concentration, with the highest absorption observed in the sample with 35 mol% Bi2O3. The direct and indirect optical band gaps decreased with adding Bi2O3 up to 15 mol%, then increased at 25 mol%, and then reduced to the lowest value at 35 mol%. The system's crystallite size grew as the amount of Bi2O3 in the sample increased, as revealed by XRD. With increasing Bi2O3 content, it was discovered that the mass attenuation coefficient (μm) and radiation shielding effectiveness rose. The effective atomic number (Zeff) values increased as Bi2O3 content grew. T0.5 values of the glass samples increased as the energy increased and decreased as the Bi2O3 concentration increased. These findings suggest that prepared glasses with high Bi2O3 concentrations have potential applications in radiation shielding and optoelectronics.