Optical Absorption Spectra Research Articles

Optical Absorption and Photoluminescence of Single-Layer Boron Nitride from a First-Principles Cumulant Approach.

The photoluminescence spectrum of a single-layer boron nitride remains elusive, marked by enigmatic satellites that hint at significant but unidentified exciton-phonon coupling. Here, by employing a first-principles approach based on the many-body cumulant expansion of the charge response, we calculate the optical absorption and photoluminescence of a single-layer boron nitride. We identify the specific exciton-phonon scattering channels and unravel their impact on the optical absorption and photoluminescence spectra, thereby providing an interpretation of the experimental features. Finally, we show that, even in a strongly polar material such as h-BN monolayer, the electron-hole interaction responsible for the excitonic effect results in the cancellation of the Frölich interaction at small phonon momenta. This effect is captured only if the invariance of the exciton-phonon matrix elements under unitary transformations in the Bloch function manifold is preserved in the calculation.

Tuning the potentials of aluminum phosphide nanotube photocatalyst for wastewater treatment through band gap engineering: a DFT study

Abstract The photocatalytic properties of semiconductor materials, which are controllable through the design of the bandgap structure, make them a promising catalyst for wastewater treatment. This work investigated the photocatalytic properties of single-walled aluminum phosphide nanotube (SWAlPNT) doped with different concentrations of boron (B) atoms for wastewater treatment. Analysis of the structural, electronic and optical properties of the SWAlPNT photocatalyst was performed using the density functional theory approach in terms of plane wave basis set and pseudopotential. The SWAlPNT was found to be stable to B doping with 3.6% and 7.1% concentrations. Cohesive energy decreases with an increase in concentration of dopant which results in efficient thermal stability. An indirect band gap value of 1.4 eV was obtained with B-doped SWAlPNT with 3.6% concentration which agreed with band gaps of other photocatalysts used for wastewater purification. Analysis using optical absorption spectra revealed that 3.6% B-doped system absorbs visible light while 7.1% doped system absorbs both visible and ultraviolet light. This study found both 3.6% and 7.1% B-doped SWAlPNT as suitable photocatalysts for wastewater treatment under solar irradiation, while the 3.6% B-doped system shows relatively better performance for wastewater treatment.

Machine learning-enabled chemical space exploration of all-inorganic perovskites for photovoltaics

The vast compositional and configurational spaces of multi-element metal halide perovskites (MHPs) result in significant challenges when designing MHPs with promising stability and optoelectronic properties. In this paper, we propose a framework for the design of B-site-alloyed ABX3 MHPs by combining density functional theory (DFT) and machine learning (ML). We performed generalized gradient approximation with Perdew–Burke–Ernzerhof functional for solids (PBEsol) on 3,159 B-site-alloyed perovskite structures using a compositional step of 1/4. Crystal graph convolution neural networks (CGCNNs) were trained on the 3159 DFT datasets to predict the decomposition energy, bandgap, and types of bandgaps. The trained CGCNN models were used to explore the compositional and configurational spaces of 41,400 B-site-alloyed ABX3 MHPs with a compositional step of 1/16, by accessing all possible configurations for each composition. The electronic band structures of the selected compounds were calculated using the hybrid functional (PBE0). Then, we calculated the optical absorption spectra and spectroscopic limited maximum efficiency of the selected compounds. Based on the DFT/ML-combined screening, 10 promising compounds with optimal bandgaps were selected, and from among these 10 compounds, CsGe0.3125Sn0.6875I3 and CsGe0.0625Pb0.3125Sn0.625Br3 were suggested as photon absorbers for single-junction and tandem solar cells, respectively. The design framework presented herein is a good starting point for the design of mixed MHPs for optoelectronic applications.

Insights on the effect of process conditions on the optical properties of silver ion exchanged soda-lime silicate glass

The effects of ion exchange time and temperature on the optical properties and plasmonic response of silver ion exchanged soda-lime silicate glass were investigated using scanning electron microscopy (SEM) in energy dispersive spectrometry (EDS) configuration, m-lines spectroscopy, photoluminescence (PL) spectroscopy, and UV–visible absorption spectroscopy. SEM analyses in EDS mode provided profiles of silver oxide molar concentration. These profiles were directly correlated to the silver diffusion coefficient using an adjustment procedure. The effective indices of ion exchanged glasses measured by the standard prism coupling technique (m-lines) allowed access to refractive index distributions in ion exchange regions. These ion-exchanged glasses underwent evaluation to determine their potential suitability for use in multimode planar systems. The PL results acquired after ion exchange demonstrated that the creation of Ag0 atoms from Ag+ ions was responsible for the decline and quenching of PL intensity at ion exchange times and temperatures increase. Silver nanoparticles were generated in the samples subjected to ion exchange at 480 °C without the need for post-exchange treatments. The emergence of the surface plasmon resonance band around 427 nm in the optical absorption spectra confirmed the formation of Ag nanoparticles in annealed glasses. Estimates of the UV–visible absorption spectra indicated an average size of silver nanoparticles ranging from 1.8 to 2.4 nm.

Experimental and numerical assessment on Pb-free alkaline mixed borate glasses for radiation resisting applications

Melt quenching technique has been used to fabricate calcium boro-phosphate glasses doped with praseodymium oxide ions. With increased P2O5 content, structural parameters like oxygen molar volume (Vo) and oxygen packing density (OPD) indicate an opposing trend. In addition to optical factors like optical electronegativity, absorption edge, and direct and indirect bandgap values being estimated and discussed, optical absorption spectra have been recorded for all the glasses. The presence of ionic bond behaviour confirms the strong structural and optical property changes caused by the P2O5 content. Using the Phy-X software application, the radiation shielding parameters were investigated. The incorporation of B2O3, CaCO3, and P2O5 offers more number of bridging oxygens which further leads to closely packed nature. Considering the glass sample B0PCM:Pr, the highest linear attenuation coefficient (LAC) is determined. The LAC results showed that at high energy levels, the glass's shielding performance became more consistent. The results of the effective atomic number analysis demonstrated the impact that CaCO3 has on the glass's shielding effectiveness, with a higher concentration of CaCO3 improving the material's defence against gamma radiation. For B0PCM:Pr glass, the half value layer (HVL) rises from 2.101 to 3.444 cm at 0.284–1.333 MeV. Certainly, it has been observed that the glass tends to have a smaller HVL when it contains more CaCO3 with lesser P2O5 content.

Enhancing Gamma-Ray Shielding with Bi2O3-Enriched BTBi Glasses: Optimal Balance of Attenuation and Glass Transparency

A host glass of barium-magnesium-boro-tellurite (BTBi0) was produced and reinforced with 10, 20, 30, and 40 mol% of Bi2O3 (BTBi1, BTBi2, BTBi3, and BTBi4) to enhance its gamma rays shielding efficiency. The structural, optical, and attenuation properties of the produced BTBi glass series were studied. Penetration of Bi2O3 up to 30 mol% into the proposed host network enriches it with non-bridging oxygens (NBO) units, while the glass containing 40 mol% was enriched with bridging oxygens (BOs) units, which arose as a result of the role of the Bi3+ ion in disrupting the borate network, leading to the conversion. The conversion role of Bi2O3 was clearly evident in the behavior of the molar volume, oxygen packing density, and packing density. The results of Raman shift showed the formation of the structural units of the boro-tellurite network and BiO6 units within the glass network. The compositional changes brought about by Bi2O3 agreed perfectly with the results of the optical properties of the studied glass. The red shift in optical absorption spectra, the reduction in the optical band gap, and the augmentation of Urbach energy up to 30 mol% of Bi2O3 occurred mainly as a result of the formation of NBOs units. In contrast, at 40 mol% of Bi2O3, the continuation of the red shift, the decrease in the optical band gap, and the increase in the Urbach energy, despite the increase in BOs compared to the NBOs, are attributed to the high polarizability of Bi3+ and the formation of BiO6 units. The transparency of the glass increased to about 85% with increasing Bi2O3 up to 30 mol%, but decreased to 70% at 40 mol%. The ability of the considered glasses to attenuate gamma rays was examined using Phy-X/PSD software. The results showed that the attenuation ability improved significantly with increasing Bi2O3 concentrations, where the required thickness to attenuate gamma rays was reduced by 48.505–77.134% at 40 mol% of Bi2O3. Based on the high attenuation ability and transparency of the studied BTBi glasses, they can be used as a protective shield against gamma rays in nuclear applications that require visual monitoring.

Theoretical investigations of structural, electronic, magnetic, and optical properties of group V (X = V, Nb, Ta) added CeO2-X materials for optoelectronic applications.

Depletion of natural resources, responsible for energy production, is a serious concern for researchers to develop alternate energy resources or materials. Scientists have proposed various energy materials which are based on semiconductors and their underlying physics. Cerium oxide (CeO2) is a versatile energy material which receives much attention owing to excellent photocatalytic, photonic, thermal stability, and optoelectronic applications. Even though CeO2 exhibited remarkable physical properties, but yet, they can be enhanced upon suitable doping. Focus on current research is to dope group V elements into CeO2 in order to enhance its electronic and optical response. The density of states (DOS) and band gaps of proposed materials are calculated, and significant improvement is noted after applying TB-mbj method. Optical absorption spectra of V/Nb/Ta-doped CeO2 show blueshift and decrease in reflectivity along with the presence of magnetism illustrate potential uses of these materials in future UV optoelectronics, spintronics, sensing, and energy harvesting devices. This research is based on computational work carried using Wien2k code where PBE-GGA approximation is used to approximate exchange and correlation potentials. Supercells of vanadium/niobium/tantalum-doped CeO2 are constructed, and spin-polarized density of states (DOS) along with optical constant are calculated. TB-mbj method is used to bring improvements in DOS and band gaps of proposed materials. Iterations are conducted using convergence criterion, and non-relativistic calculations are performed.

Crystal structures and photoluminescence properties of undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders

Undoped and Fe3+ doped Li2Ba3(P2O7)2 pyrophosphate nanopowders were produced by a solid-state reaction process. The prepared samples underwent characterizations using XRD, SEM with EDS, HR-TEM with SAED, FTIR, Raman, UV-Vis, EPR and PL techniques. The XRD analysis confirms the orthorhombic crystal structure of the prepared samples and unit cell parameters were evaluated. The samples exhibited stone-like structures with low aggregation based on the micrographs obtained from SEM and HR-TEM images. Additionally, the grain and particle sizes of the powder samples were evaluated. The elements Li, O, P, Ba and Fe were confirmed to be present in the produced samples by EDS spectra. FT-IR and Raman spectral investigation revealed the fundamental vibrational and bending modes of various phosphate groups. The energy bands, identified as characteristic bands of Fe3+ ions, were produced in the UV–visible region of the optical absorption spectrum for the doped sample. The crystal field and inter-electronic parameters (Dq = 915, B = 700 and C = 2715 cm−1) were also evaluated. Furthermore, the refractive index and metallization criteria properties were calculated using energy bandgap values of 4.46 and 4.38 eV of the produced samples. The doping of Fe3+ ions led to a reduction in the bandgap energy, resulting in a red-shift. A resonance signal was observed in the EPR spectrum at g = 2.05, which can be ascribed to iron ions entering the host lattice at a distorted octahedral symmetry sites and this was also supported by optical absorption studies. The produced sample showed emission peaks at 354, 440 and 530 nm in the ultraviolet, blue and green regions of its photoluminescence spectrum. Photometric parameters, such as CCT, CRI and CIE chromatic coordinates, reveal that the prepared samples could bee used in LEDs applications. This work offers novel visions into diphosphate compounds doped with transition metal ions.

Impact of Peripheral Hydrogen Bond on Electronic Properties of the Primary Acceptor Chlorophyll in the Reaction Center of Photosystem I.

Photosystem I (PS I) is a photosynthetic pigment-protein complex that absorbs light and uses the absorbed energy to initiate electron transfer. Electron transfer has been shown to occur concurrently along two (A- and B-) branches of reaction center (RC) cofactors. The electron transfer chain originates from a special pair of chlorophyll a molecules (P700), followed by two chlorophylls and one phylloquinone in each branch (denoted as A-1, A0, A1, respectively), converging in a single iron-sulfur complex Fx. While there is a consensus that the ultimate electron donor-acceptor pair is P700+A0-, the involvement of A-1 in electron transfer, as well as the mechanism of the very first step in the charge separation sequence, has been under debate. To resolve this question, multiple groups have targeted electron transfer cofactors by site-directed mutations. In this work, the peripheral hydrogen bonds to keto groups of A0 chlorophylls have been disrupted by mutagenesis. Four mutants were generated: PsaA-Y692F; PsaB-Y667F; PsaB-Y667A; and a double mutant PsaA-Y692F/PsaB-Y667F. Contrary to expectations, but in agreement with density functional theory modeling, the removal of the hydrogen bond by Tyr → Phe substitution was found to have a negligible effect on redox potentials and optical absorption spectra of respective chlorophylls. In contrast, Tyr → Ala substitution was shown to have a fatal effect on the PS I function. It is thus inferred that PsaA-Y692 and PsaB-Y667 residues have primarily structural significance, and their ability to coordinate respective chlorophylls in electron transfer via hydrogen bond plays a minor role.

Theoretical investigation on the optical absorption spectra in cyclo[[formula omitted]]carbons ([formula omitted] 10, 14, 18)

The optical absorption spectra of cyclo[n]carbons (n= 10, 14, 18) are investigated in the framework of time-dependent density functional theory. The collective plasmon excitations well develop as the increases of the ring size and the symmetry group of cyclo[n]carbons. An increase in intensity for the main peaks with the growing number of atoms in cyclo[n]carbons is observed. With the increase of the radius of the monocyclic ring, as more electrons participate in the dipole oscillation the main excitation peaks are red-shifted to the lower energy. The highly symmetrical structures of cyclo[n]carbons (Dnh) possess degenerate levels, leading to simpler spectra with fewer peaks. The Fourier transform of the induced electron density of the cyclo[n]carbons (n= 10, 14, 18) is investigated at the excitation frequencies.

Characterizing the properties of Li2O–B2O3–SiO2– P2O5–TiO2 glasses: A multidimensional investigation of their structure, optical properties, and gamma-ray shielding capability

A series of lithium borophosphosilicate glass doped with TiO2 was produced with melt-quenching procedure with empirical formula (20-x) Li2O–40B2O3–20SiO2– 20P2O5–xTiO2, where x can be changed between 0 and 16 mol%. By adding titanate, the bulk density of BSPLT glass increased from 3.61 to 4.812 g/cm3. The amorphous nature of glasses is demonstrated by XRD analysis. Different optical characteristics, including the refractive index and optical band gap (Eopt), were determined by recording optical absorption spectra in the 250–2500 nm range. The observed range (Eopt) values from 3.09 eV to 2.64 eV suggests that the (Eopt) decreases as the content of TiO2 in the BSPLT samples increases. The linear optical susceptibility χ(1), third-order non-linear optical susceptibility (χ(3)), and the non-linear refractive index (n2) were determined. Higher-density glasses provide more effective radiation shielding because they are better at absorbing and slowing down radiation particles. BSPLT-16 glass exhibits the highest FNRCS value among the samples tested, indicating its superior performance in shielding against fast neutrons. It is noted that the BSPLT-16 sample, has the highest density among the glasses tested, shows the greatest effective for radiation shielding applications according to the results.

PigmentHunter: A point-and-click application for automated chlorophyll-protein simulations.

Chlorophyll proteins (CPs) are the workhorses of biological photosynthesis, working together to absorb solar energy, transfer it to chemically active reaction centers, and control the charge-separation process that drives its storage as chemical energy. Yet predicting CP optical and electronic properties remains a serious challenge, driven by the computational difficulty of treating large, electronically coupled molecular pigments embedded in a dynamically structured protein environment. To address this challenge, we introduce here an analysis tool called PigmentHunter, which automates the process of preparing CP structures for molecular dynamics (MD), running short MD simulations on the nanoHUB.org science gateway, and then using electrostatic and steric analysis routines to predict optical absorption, fluorescence, and circular dichroism spectra within a Frenkel exciton model. Inter-pigment couplings are evaluated using point-dipole or transition-charge coupling models, while site energies can be estimated using both electrostatic and ring-deformation approaches. The package is built in a Jupyter Notebook environment, with a point-and-click interface that can be used either to manually prepare individual structures or to batch-process many structures at once. We illustrate PigmentHunter's capabilities with example simulations on spectral line shapes in the light harvesting 2 complex, site energies in the Fenna-Matthews-Olson protein, and ring deformation in photosystems I and II.

Comparison of optical absorption and diffuse reflectance spectra techniques for determining the optical energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite

Ultrafine particles of Ni0.5Mn0.5Fe2O4 were synthesized by coprecipitation technique to study the effect of both physical forms (ferrofluid and powder) and thermal treatment (drying at 100 °C and calcination at 600 °C for two hours) on the structural properties of Ni0.5Mn0.5Fe2O4 nanoferrite. In addition, the work presents a comparison between using optical absorption and optical diffuse reflectance spectra in studying the optical direct energy band gap. x-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the phase, size, and morphology of dried and calcined Ni0.5Mn0.5Fe2O4 nanoparticles, respectively. Fourier transform infrared (FTIR) spectra revealed the characteristic peaks of the synthesized ferrite and provided further information on the functional groups. The optical absorption spectra were used to evaluate the optical direct energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite as a ferrofluid, whereas, the optical diffuse reflectance spectra were used to evaluate the optical direct energy band gap of dried and calcined Ni0.5Mn0.5Fe2O4 nanoferrite in powder form.

First-principles calculations to investigate electronic, magnetic, and optical properties at (110) and (111) surfaces of Ni adsorption on CdO

In this study, we utilised the GGA+U method via the WIEN2k software to investigate the structural, magnetic, and optoelectronic responses of two distinct surfaces, (111) and (110), to Ni adsorption on CdO at the Cd site. The analysis revealed that Ni/CdO (111) demonstrates properties akin to a semimetal or a zero-gap semiconductor across both spin orientations, while Ni/CdO (110) exhibits a metallic nature under similar conditions. These phenomena are predominantly ascribed to the orbital contributions from Ni-d, Cd-d, and O-p for the Ni/CdO (111), and Ni-d, Cd-d, and O-s for the Ni/CdO (110), respectively. A notable blue shift in the optical absorption spectra was observed for both materials. Utilising the Dielectric function, we calculated the dispersion of energy bands along with essential optical properties, including the absorption coefficient, energy loss function, and reflectivity, refractive index, and extinction coefficient. Magnetisation values for Ni/CdO (110) and Ni/CdO (111) were recorded at (−0.11794) µB and (2.17926) µB, respectively, influenced by the absorption spectrum's blue shift. Additionally, transport properties were evaluated using the BoltzTraP software over a temperature range of 0 to 800 K. Our findings suggest that Ni/CdO (110) and Ni/CdO (111) are significant for applications in spintronics and energy devices.

Synthesis and Characterization of Superhydrophobic Epoxy Resin Coating with SiO2@CuO/HDTMS for Enhanced Self-Cleaning, Photocatalytic, and Corrosion-Resistant Properties.

The exceptional corrosion resistance and combined physical and chemical self-cleaning capabilities of superhydrophobic photocatalytic coatings have sparked significant interest among researchers. In this paper, we propose an economical and eco-friendly superhydrophobic epoxy resin coating that incorporates SiO2@CuO/HDTMS nanoparticles modified with Hexadecyltrimethoxysilane (HDTMS). The application of superhydrophobic coatings effectively reduces the contact area between the metal surface and corrosive media, leading to a decreased corrosion rate. Additionally, the incorporation of nanomaterials, exemplified by SiO2@CuO core-shell nanoparticles, improves the adhesion and durability of the coatings on aluminum alloy substrates. Experimental data from Tafel curve analysis and electrochemical impedance spectroscopy (EIS) confirm the superior corrosion resistance of the superhydrophobic modified aluminum alloy surface compared to untreated surfaces. Estimations indicate a significant reduction in corrosion rate after superhydrophobic treatment. Furthermore, an optical absorption spectra analysis of the core-shell nanoparticles demonstrates their suitability for photocatalytic applications, showcasing their potential contribution to enhancing the overall performance of the coated surfaces. This research underscores the promising approach of combining superhydrophobic properties with photocatalytic capabilities to develop advanced surface modification techniques for enhanced corrosion resistance and functional properties in diverse industrial settings.

A study on structural and electronic properties of WS2/SnS2 composite thin films by CBD method

The composite WS2/SnS2 thin films deposited by CBD have been studied for variations in deposition time and sulfur concentration. XRD results show a polycrystalline hexagonal phase with crystallite size varying from ∼ 3.56 nm to ∼ 16.35 nm in composite thin films. The optical absorption spectra of S-2 show maximum absorption peaks in 380 nm to 800 nm. The band gap was calculated to be ∼ 1.52 eV to ∼ 2.5 eV. We measured the current–voltage characteristics across the junction to determine the transport properties. A photodetector application involving the WS2/SnS2 composite structure shows a maximum specific detectivity of 6.2 x 1013 Jones. The reason for varying the electrical parameters discussed in this work.

Synthesis and characterization of Bi2O3–B2O3–SiO2–MgO glasses: Structural, optical, and shielding properties

The systematic investigation of the impact of Bi2O3 on the structural, spectroscopic, and radiation features of 15SiO2 - 75B2O3 - (10-x) MgO - xBi2O3, x= (0 ≤ x ≥ 10) glasses were studied. The increase in glass density as Bi2O3 content increase is due to the incorporation of Bi2O3 into the glass network. XRD patterns indicate an amorphous, glassy nature of the glasses. The optical absorption spectra suggest that as the content of Bi2O3 increases, the optical band gap (Eopt.) widens and the Urbach energy (Eu) decreases. It has been observed that the opposite trend between the (Eopt.) and (Eu). The radiation shielding characteristics of MgBi glasses have been evaluated through the assessment of several fundamental radiation attenuation variables. As Bi2O3 content increases would enhance properties like (HVL), (MFP), and (Zeq), especially at lower energy ranges. Adding Bi2O3 to the glassy system has a positive impact on enhancing its neutron attenuation ability. The MgBi-10 glass has the best shielding performance against fast neutrons. The MgBi-10 glass sample shows promising properties for optical and radiation shielding purposes.

From monomer to polymer: Controlled synthesis and comprehensive analysis of poly(p-phenylene vinylene) via ROMP

This study focuses on synthesis and evaluation of [2.2] paracyclophane-1,9-diene to produce a soluble poly(p-phenylenevinylene) (PPV) derivative homopolymer using ring-opening metathesis polymerization (ROMP). The resulting homopolymer displayed a narrow polydispersity index (PDI) of 1.22, indicating precise control over polymerization. The PPV derivative exhibited excellent solubility in various organic solvents. Photophysical properties, including optical absorption and fluorescence emission spectra, were investigated to evaluate utilization in optoelectronic devices. Optical band gaps ranged from 2.21 to 2.25 eV for thin films and 2.07 to 2.19 eV for solutions, while the electrochemical band gap, determined by cyclic voltammetry, was 2.37 eV. These materials demonstrated promising fluorescence activity in various solvents and thin films, suggesting potential applications in organic light-emitting diodes (OLEDs) and related optoelectronic devices.

Entropy-Enthalpy Compensation in Electron-Transfer Processes.

Solvent reorganization energies, free energies, and entropies are obtained for photoexcitation of three molecules that exhibit strong solvatochromism [Nile red, 5-(dimethylamino)-5'-nitro-2,2-bisthiophene, and Reichardt's dye B30] by measuring their optical absorption spectra at temperatures between 150 and 300 K in solvents with a range of polarities. Energies, free energies, and entropies of solvent reorganization are also obtained from computer simulations of three intramolecular electron-transfer reactions (charge separation and recombination in Zn-porphyrin-quinone cyclophane and charge transfer in a bis-biphenylandrostane radical anion). Entropy-enthalpy compensation in the solvent reorganization free energy for photoexcitation or electron transfer is found to be essentially complete (having nearly equal and opposite contributions from entropic and enthalpic effects) for all of the processes with solvent reorganization energies less than about 0.1 eV. Compensation becomes less complete as the reorganization energy becomes larger. A semiclassical treatment of the solvent reorganization entropy can rationalize these results.

Electronic and optical properties of two-dimensional Janus Sn0.5Ge0.5S monolayer

Janus two-dimensional (2D) materials have received widespread attention in recent years due to their out-of-plane asymmetric structures which makes them promising candidates for sustainable energy devices. In this work, using first-principles calculations, we study a novel 2D Janus monolayer Sn0.5Ge0.5S for recently synthesized SnS monolayer. We investigate structural, electronic and optical properties of this new 2D Janus material. Our results show that monolayer Sn0.5Ge0.5S is an indirect band gap semiconductor with the lowest conduction band is nearly flat around the band minimum. Atom projected band structure reveals that this flattened valley is mainly originated from orbitals of Sn atom. In addition, the inclusion of spin–orbit coupling leads to splitting of the bands, largely along Γ-Y direction. Optical absorption spectra indicate superior sunlight absorption in the visible and ultraviolet regions. Interestingly, absorption spectra of Janus monolayer Sn0.5Ge0.5S are polarization dependent owing to its anisotropic crystal structure along zigzag and armchair directions.