Decrease In Band Gap Research Articles

Effect of Fe doping on structural, optical and magnetic properties of CdS quantum dots

Abstract Pure CdS nanoparticles and Fe-doped CdS quantum dots (Cd₁₋ₓFeₓS, where x = 0.0, 0.03, 0.06, 0.09, and 0.12) were successfully synthesized using the co-precipitation method. X-ray diffraction (XRD) analysis confirmed the cubic phase structure of CdS without additional peaks, indicating the effective incorporation of Fe ions into the CdS lattice. The crystallite size exhibited a gradual increase with increasing Fe content. High-resolution transmission electron microscopy (HR-TEM) revealed a well-defined spherical morphology for pure CdS, while Fe doping induced notable agglomeration in the quantum dots. X-ray photoelectron spectroscopy (XPS) confirmed the formation of the CdFeS composition and provided insights into the valence states of Cd, Fe, and S. UV-Vis diffuse reflectance spectroscopy (DRS) demonstrated a decrease in the optical band gap from 2.29 eV to 2.18 eV with Fe doping, indicating a modification of the electronic structure. Magnetization studies revealed a transition from diamagnetic behavior in pure CdS to ferromagnetic behavior in Fe-doped samples. Additionally, Fe doping significantly influenced the magnetic parameters, including saturation magnetization, remanence, and coercivity. These results highlight the structural, optical, and magnetic properties of CdS can be tuned through Fe doping, making these materials promising candidates for optoelectronic and spintronic applications.
Keywords: CdS quantum dots, XRD, XPS, optical energy gap, ferromagnetism.

Crossover of Frenkel and Wannier-Mott Excitons Through Halide Composition Tuning in Mixed Halide Perovskites.

Using first-principles G0W0 (G0 is one-electron Green's function and W0 is the dynamical screening Coloumb potential) coupled Bethe-Salpeter equation (BSE)calculations with spin-orbit coupling, exceptionally strong excitonic effects are identified in several bismuth-based vacancy-ordered mixed halide double perovskites. These perovskites are thermodynamically stable with negative formation energy. For Cs3Bi2X9 (X = Cl,Br,I) double perovskites, both the bandgap and excitonic binding energy decrease as the size of the halogen atom increases. The excitonic effects can be tuned in mixed halide perovskites such as Cs3Bi2I6Cl3, Cs3Bi2I6Br3, Cs3Bi2Br6I3, Cs3Bi2Cl6Br3, Cs3Bi2Br6Cl3, and Cs3Bi2Cl6I3. This study reports the exciton radiative lifetimes of the vacancy-ordered perovskites, revealing that these excitons exhibit long radiative lifetimes, particularly for Cs3Bi2Br6I3 with 11141 at 300 K and 24 at 5 K. The long radiative lifetimes are linked to the delocalization of the exciton (Wannier-Mott type) in real space, whereas the more localized exciton (Frenkel type) in Cs3Bi2Cl6Br3 results in shorter radiative lifetimes of 155 at 300 K and 334 ns at 5 K. Due to their long exciton lifetime, these materials present interesting opportunities for photovoltaicapplications.

Phase transitions, Dirac and Weyl semimetal states in Mn1−xGexBi2Te4

Using angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT), an experimental and theoretical study of changes in the electronic structure (dispersion dependencies) and corresponding modification of the energy band gap at the Dirac point (DP) for topological insulator (TI) have been carried out with gradual replacement of magnetic Mn atoms by non-magnetic Ge atoms when concentration of the latter was varied from 10% to 75%. It was shown that when Ge concentration increases, the bulk band gap decreases and reaches zero plateau in the concentration range of 45–60% while trivial surface states (TrSS) are present and exhibit an energy splitting of 100 and 70 meV in different types of measurements. It was also shown that TSS disappear from the measured band dispersions at a Ge concentration of about 40%. DFT calculations of band structure were carried out to identify the nature of observed band dispersion features and to analyze the possibility of magnetic Weyl semimetal state formation in this system. These calculations were performed for both antiferromagnetic (AFM) and ferromagnetic (FM) ordering types while the spin-orbit coupling (SOC) strength was varied or a strain (compression or tension) along the c-axis was applied. Calculations show that two different series of topological phase transitions (TPTs) may be implemented in this system, depending on the magnetic ordering. In the case of AFM ordering, the transition between TI and the trivial insulator phase passes through the Dirac semimetal state, whereas for FM phase such route admits three intermediate states instead of one (TI—Dirac semimetal—Weyl semimetal—Dirac semimetal—trivial insulator). Weyl points that form in the FM system along the direction annihilate when either the SOC strength decreases or a sufficient tensile strain is applied, which is accompanied by the corresponding TPTs. Model calculations of the influence of local magnetic ordering in AFM were carried out by alternating Mn layers with Ge-doped layers and showed that the magnetic Weyl semimetal state in this system is reachable at a Ge concentration of approximately 40% without application of any external magnetic fields.

Investigation of Magnetism and Photocatalytic Activity Using Biomass‐Derived Carbon Dots

AbstractA cost‐effective and green synthesis method was adopted for the synthesis of carbon dots (CDs) using easily available biomass, namely, Triticum (wheat), by varying the pyrolysis time. The synthesized CDs are labeled as A 1h, A 2h, and A 3h, respectively, where “A” represents the raw material, and “1h,” “2h,” and “3h” denote the respective pyrolysis time. XRD analysis reveals the turbostratic nature of the synthesized CDs. The size and shape of synthesized samples were visualized by HRTEM images. The bandgap was calculated by Tauc's plot and was determined to be 3.66, 5.08, and 4.89 eV for A 1h, A 2h, and A 3h, respectively. FTIR measurement analyzed the functional groups present on the surface of CDs. VSM measurement confirms the ferromagnetic behavior of CDs. Synthesized CDs have been used for photocatalytic degradation of rose bengal (RB) dye under UV light irradiation. Photocatalytic degradation increases with a decrease in bandgap and the maximum degradation efficiency (90.28%) was obtained for A 1h sample.

Pressure-dependent optoelectronic properties of antiperovskite derivatives X3AsCl3 (X = Mg, Ca, Sr, Ba): a first-principles study.

The success of halide perovskites in the field of optoelectronics has sparked extensive exploration of perovskite-type compounds, including antiperovskites and perovskite derivatives. Recently, a class of antiperovskite derivatives, X3MA3, has been proposed as potential photovoltaic absorbers. These antiperovskite derivatives share a similar crystal structure with perovskites, featuring a corner-sharing octahedral framework. In this work, we employed first-principles calculations to investigate the evolution of the structural and optoelectronic properties of four antiperovskite derivatives X3AsCl3 (X = Mg, Ca, Sr, Ba) under hydrostatic pressures ranging from 0 to 4 GPa. Our results show that these properties change linearly with pressure, with the structure and electronic properties of Ba3AsCl3 being particularly sensitive to pressure. At 4 GPa, its band gap and lattice constant decrease by 0.37 eV and 0.251 Å, respectively. Notably, Ba3AsCl3 achieves a high theoretical conversion efficiency exceeding 30% under moderate pressure. Our research suggests that Ba3AsCl3 may be a promising candidate for future optoelectronic devices, particularly under compressed epitaxial strain.

Impact of bath temperature on the optical, structural, and photoelectrochemical properties of thin films of copper (II) oxide synthesized via electrodeposition method

Impact of bath temperature on the optical, structural, and photoelectrochemical properties of thin films of copper (II) oxide synthesized via electrodeposition method

Comparative performance analysis of mixed metal oxide sensors for dual-sensing leveraging machine learning

This paper presents the synthesis of mixed metal oxide (BaTiO3: ZnO) (B: Z) sensors with various molar ratios using a low-temperature hydrothermal method for dual sensing applications (gas and acceleration). The sensor developed with an equal molar ratio of 1B:1Z, showcases superior performance compared to unmixed and alternative mixed metal oxide sensors. This equilibrium in ratios optimally enhances synergistic effects between elements B and Z, resulting in improved sensing properties. Furthermore, it contributes to structural stability, enhancing performance in gas and acceleration sensing. A decreased band gap of 2.82 eV and a rapid turn-on voltage of 0.18 V were achieved. The acceleration performance of 1B:1Z sensor exhibits a maximum voltage of 2.62 V at a 10 Hz resonant frequency and an output voltage of 2.52 V at 1 g acceleration, achieving an improved sensitivity of 3.889 V g-1. In addition, the proposed gas shows a notable sensor response of ∼63.45% (CO) and 58.29% (CH4) at 10 ppm with a quick response time of 1.19 s (CO) and 8.69 s (CH4) and recovery time of 2.09 s (CO) and 8.69 s (CH4). Challenges in selectivity are addressed using machine learning, employing various classification algorithms. Linear discriminant analysis achieves superior accuracy in differentiating between CO and CH4,reaching 96.6% for CO and 74.6% for CH4at 10 ppm. Understanding these concentration-dependent trends can guide the optimal use of the sensors in different current applications.

A comparative hybrid-DFT study of energy-efficient halide perovskite under hydrostatic pressure

Abstract To accomplish the primary aim of this research, follow these steps to conduct a thorough computational evaluation by using the Heyd–Scuseria–Ernzerhof (HSE-03) hybrid functional. This analysis will cover the structural, electrical, elastic, mechanical, anisotropic and optical properties of halide perovskite materials CsPbX3 (X = Cl, Br, and I) by applying pressure from 0 to 25 GPa. Under stress, all materials exhibit consistent decrease in lattice parameters and decrease in band-gap up to 25 GPa. To explore the electronic band structure (BS), we have estimated the TDOS (Total Density of States) and EPDOS (Elemental Partial Density of States). To further assess the material's relevance, we calculated several optical properties including absorption I (ω), extinction coefficient k (ω), refractive index n (ω), loss function L (ω), reflectivity R (ω), real part of the dielectric function ε_1 (ω) and the imaginary part ε_2 (ω). The static values of reflectivity R (ω), real part of the dielectric function ε_1 (ω) increases by applying pressure in all materials. With the pressure application, the peak of absorption peak under study perovskites shifts markedly towards higher photon energies. Moreover, its high refractive index, reflectivity and absorption, make it an important element for optoelectronic devices. The structure retains its cubic form and there is no change in phase in all three materials. The materials are stiff, unyielding, and mechanically stable demonstrating elevated resistance to shear stress based on different mechanical and elastic parameters, including Young’s modulus , bulk modulus and shear modulus. The Pugh/Frantsevich ratios, Kleinman’s parameter, Cauchy pressure and Poisson’s ratio, indicate the ductility of materials, metallic bonding characteristics, and resilience under high pressure. Additionally, distinctive anisotropy factors are used to confirm the material's anisotropic properties.

Enhancing the structural and optoelectronic properties of carboxymethyl cellulose sodium filled with ZnO/GO and CuO/GO nanocomposites for antimicrobial packaging applications.

One of the biggest challenges in food packaging is the creation of sustainable and eco-friendly packaging materials to shield foods from ultraviolet (UV) photochemical damage and to preserve the distinctive physical, chemical, and biological characteristics of foods throughout the supply chain. Accordingly, this study focuses on enhancing the UV shielding properties and biological activity of carboxylmethyl cellulose sodium (CMC) through modifications using zinc oxide (ZnO), copper oxide (CuO), and graphene oxide (GO) using the solution casting technique. The hybrid nanocomposites were characterized by fourier-transform infrared (FTIR) spectrophotometer, ultraviolet-visible (UV-Vis) spectrophotometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and x-ray diffraction (XRD). Significant interactions between CMC and the metal oxide/GO nanocomposites were revealed by FTIR analysis, which reflects the formation of hydrogen bonding between CMC and the nanocomposites. XRD confirmed the functionalization of CMC with ZnO/GO and CuO/GO nanocomposites. Additionally, the CMC film showed a decrease in the optical bandgap from 5.53 to 3.43eV with improved UV shielding capacity. Moreover, the composite films had excellent refractive index and optical conductivity values of 1.97 and 1.56 × 1010Ωcm- 1, respectively. SEM and EDX analysis confirmed the formation of ZnO/GO and CuO/GO within the CMC matrix. Thus, dedicates that the CMC nanocomposites have promising applications in packaging materials. These results were confirmed by the quantum mechanical calculations utilizing density functional theory (DFT). Total dipole moment (TDM), frontier molecular orbitals (FMOs), chemical reactivity descriptors, and molecular electrostatic potential (MESP) maps were all studied using the B3LYP/LanL2DZ model. The TDM and FMO investigations revealed that the CMC/CuO/GO model has the highest TDM (84.031 Debye) and the smallest band gap energy (0.118eV). Moreover, CMC's reactivity increased after CuO/GO nanocomposites integration, as demonstrated by MESP mapping. Finally, the antibacterial activity of pure CMC, CMC/ZnO/GO, and CMC/CuO/GO nanocomposite films was evaluated against Staphylococcus aureus and Escherichia coli. The zones of inhibition data showed that both CMC/ZnO/GO and CMC/CuO/GO exhibited higher antibacterial activity than CMC alone, particularly against S. aureus. The inhibition zones for CMC/ZnO/GO and CMC/CuO/GO against S. aureus were 16mm and 14mm, respectively, suggesting enhanced susceptibility of S. aureus compared to E. coli. These results highlight the significant potential of ZnO and CuO NPs in improving the antimicrobial efficacy of CMC nanocomposites.

Electric field induced bandgap enlargement of S- and N-hyperdoped silicon

In this paper, the effect of the electric field on the electronic structure of S-hyperdoped silicon and N-hyperdoped silicon is studied in detail by theory. The results show that the total bandgap initially increases and subsequently decreases with the increase of the electric field. Specifically, at an electric field of 0.1 V, the total bandgap reaches the maximum. With further increasing the electric field, the total bandgap decreases, but it is still larger than that in the absence of any electric field. The bandgap difference of the configuration in 2 × 2 × 2 supercell with and without electric field is approximately 0.2 eV. When 0.1 V of the electric field in the x and y directions is applied to the 2 × 2 × 3 supercell of the S- and N-hyperdoped silicon, the changes of the electronic structure are consistent. However, the band gap expansion is more obvious than that in the z direction electric field. While for 3 × 3 × 2 supercells of the S- and N-hyperdoped silicon, the band gap expansion is more significant under the z direction electric field than that under electric fields in the x and y directions. The difference in the bandgap variation under different directions of the electric field should be due to the direction-dependence of the impurity density in the 2 × 2 × 3 and 3 × 3 × 2 supercells. The results indicate that applying an electric field can further enlarge the bandgap of the S- and N-hyperdoped silicon and bring it closer to the optimal bandgap of an intermediate-band photovoltaic material.

A Novel Turn‐On Fluorescence Probe for Selective Picomolar Detection of Uric Acid Using Green Carbon Dots (G‐NCDs) from Waste Brachyura Shells

AbstractIn the current study, a Novel synthesis of fluorescent Green carbon dots (G‐NCDs) is reported from waste Brachyura shells using a simple, green technique. G‐NCDs function as a TURN‐ON fluorescent probe for the selective detection Uric Acid (UA) in presence of Dopamine (DA). The synthesized carbon dots are sand colored under visible light and exhibit pale green fluorescence under UV radiation. The G‐NCDs are characterized using UV–vis, FTIR, XPS, SEM‐EDAX, HR‐TEM, X‐ray diffraction, and PL spectroscopic technique. The SEM‐EDAX data of G‐NCDs shows a layered, fibrous morphology and confirms the presence of only Carbon, Nitrogen, and Oxygen in the matrix. FTIR and XPS response confirms the presence of functional groups like ─C≡N, ─C≡C─, CH, ═C─H, O─H on the surface of G‐NCDs. XRD data confirms G‐NCDs to be crystalline with a particle size of 4.51 nm. The quantum yield found to be 99.8%. PL response confirms a TURN OFF fluorescence with increased addition of DA. Fluorescence resonance energy transfer (FRET), a form of dynamic quenching is responsible for the DA quenching, confirmed through linear Stern‐ Volmer plot. With increase in addition of UA in presence of DA fluorescence TURNs ON with a minimum selective detection limit of UA as 0.23 × 10−12 M. Selective detection of UA in presence of DA is due to the following reasons i) decrease in bandgap of G‐NCDs in presence of UA ii) electrostatic attraction between negatively charged carboxyl group of G‐NCDs and positively charge secondary amine group of UA molecule ii) UA molecules near to the surface of G‐NCDs switches off the formation of polydopamine iv) formation of surface defects due to the formation of hydrogen bonds between the ketone/hydroxyl group in the UA molecule and the amino group on the surface of G‐NCD resulting in fluorescence. The first time the lowest detection limit of 0.23 × 10−12 M of UA is been reported in presence of DA using G‐NCDs. In future, G‐NCDs will be used for the detection of UA in biological fluids.

AMPS-1D Simulation of P3HT Solar Cells: Impact of HOMO-LUMO Offset, Thickness, Temperature, and Optical Bandgap on Performance

This study employed the AMPS-1D software to investigate the relationship between the open-circuit voltage (Voc) and the energy difference between the Highest Occupied Molecular Orbital (HOMO) of the donor and the Lowest Unoccupied Molecular Orbital (LUMO) of the acceptor in P3HT:PCBM bulk heterojunction organic solar cells. The findings indicate a correlation between Voc and the HOMO-LUMO offset up to 1.1 eV, after which Voc remains constant. This behavior is further elucidated using a theorem based on the quasi-Fermi level, which predicts a Voc of 0.64 V, in good agreement with our simulation result of 0.68 V. The Power Conversion Efficiency (PCE) of the solar cell was studied with respect to the active layer thickness, demonstrating an increase in PCE up to 0.40 μm followed by a decrease, yielding a maximum PCE of 5.023%, consistent with the literature. The effect of temperature on PCE was also examined, demonstrating an increase in PCE with decreasing temperature in the range of 150–320 K, with a performance of 6.371% at 150 K. Furthermore, the impact of the optical bandgap on PCE was explored, showing that the PCE increased with a decrease in the optical bandgap of the P3HT:PCBM solar cell, reaching 9.94% when the optical bandgap was 1.5 eV. These findings provide valuable insights into the optimization of the performance of organic solar cells by manipulating key parameters, such as the HOMO-LUMO offset, active layer thickness, temperature, and optical bandgap.

Sulphanilamide degradation by undoped and copper doped ZnO, and ferromagnetic properties of fresh, aged, and heat-treated aged ZnO

This work looks into how well Cu-doped zinc oxide works as a photocatalyst when exposed to visible light to break down sulphanilamide. The synthesized samples were characterized by XRD and then FTIR techniques for structural besides compositional analysis. The approximate value of bandgap found out by NBE values of PL spectra showed a decrease in bandgap with doping. Deconvoluted PL spectra revealed the presence of radiative recombination pathways associated with zinc interstitial and zinc vacancy in addition to band-to-band recombination in all samples. FESEM images showed a nanoflake shape for pure ZnO, while Cu-ZnO had a pseudo-spherical shape. SQUID-VSM was adopted to understand the magnetic nature of freshly prepared, heated, and unheated aged samples. Ferromagnetic behavior was observed with saturation magnetization of 5.56×10-4, 2.88×10-4, and 2.78×10-4 emu/g for freshly prepared, heated, and unheated aged samples, respectively. A 2% Cu-doped sample exhibited the highest efficiency of 92.3% towards the degradation of sulphanilamide. Since we got better efficiency for 2% Cu-ZnO, we should further decrease the doping percentage and check whether we will get even higher efficiency in the future. The photocatalytic degradation efficiency of ternary ZnO compounds, codoped ZnO, should be evaluated, yet another future scope.

Preparation and excitation power-dependent photoluminescence of tetrapod-quantum wells

Abstract Tetrapod-quantum wells (TWs) with CdSe core and quantum wells in gradient alloyed CdSeS arms were synthesized by one-pot colloidal method. The UV-Vis absorption, photoluminescence (PL), and excitation power dependent PL properties of TWs prepared within a 30-minute reaction time were investigated. Their PL spectrum exhibited two emission peaks centered at 2.187 eV and 2.207 eV due to radiative transitions within the core and quantum wells, respectively. Analysis of the excitation power dependent PL spectra showed that the core and quantum wells’ radiative recombination channels are independent up to the excitation power density of 2.29 × 102 mW/cm2. At higher power densities, efficient carrier transfer from the quantum wells into the cores occurred. This can be explained by the state filling of quantum wells and the decreasing band gap energy of gradient alloyed CdSeS arms towards the CdSe core.

Strain induced crystal lattice softening and improved thermoelectric performance of hydrogenated silicene for energy harvesting applications

In recent years, Silicene has attracted great interest in various fields but does not fit well in the field of thermoelectrics due to the absence of electronic band gap. Nevertheless, hydrogenation of silicene (SiH) delocalize the free electrons and induces gap widening (2.19 eV), but its thermoelectric performance is still limited due to the larger band gap. Thermoelectric performance can be effectively improved using strain engineering, which allows modulation of crystal as well as electronic energy levels of a material. We studied the effect of biaxial tensile strain on structure, stability and thermoelectric properties of SiH monolayer. Taking clue regarding the stability from phonon dispersion, tensile strain upto 14% is incorporated and results are discussed. The distortion of crystal structure with strain manipulates the characteristics of electronic band structure such that there is an indirect to direct band gap transition along with decrease in band gap, effective mass and relaxation time of carriers. As a result, the Seebeck coefficient falls and attains minimum value at 14% strain while electrical conductivity and electronic thermal conductivity shows increasing trend and maximize at 14% strain. Another crucial consequence of strain is that tensile strain led to a considerable decrease in lattice thermal conductivity. At a strain of 14%, the lattice thermal conductivity at 700 K (0.28) decreased by approximately 43% compared to its unstrained counterpart (0.49 K), which is highly beneficial for achieving high ZT. To assess the efficiency of thermoelectric conversion, the ZT is computed, revealing an increase from 1.66 in the unstrained state to 2.83 at a strain of 14% and a temperature of 700 K. The calculations unveil a nearly twofold increase in ZT with the implementation of strain engineering, underscoring its effectiveness in augmenting the efficiency of thermoelectric devices.

Experimental and computational study of Bi2O3/WO3 heterostructures as efficient solar driven photocatalyst

Experimental and computational study of Bi2O3/WO3 heterostructures as efficient solar driven photocatalyst

Fabrication of CuS-MoO3 nanocomposite for high-performance photocatalysis and biosensing

Fabrication of CuS-MoO3 nanocomposite for high-performance photocatalysis and biosensing

Structural and optical evolution in CeO2 films induced by aluminum doping: A comprehensive study

Structural and optical evolution in CeO2 films induced by aluminum doping: A comprehensive study

Biofabrication and Characterisation of Ni‐Doped SnO2 Nanoparticles With Enhanced Cytotoxicity, Antioxidant, Antimicrobial and Photocatalytic Activities

ABSTRACTThe present work focuses on Annona muricata leaf extract–mediated green synthesis of pure and nickel‐doped tin oxide nanoparticles for 3%, 5% and 7% concentrations. The properties of the obtained nanoparticles were investigated through XRD, FTIR, XPS, HRTEM–SAED, SEM–EDX and UV–visible spectroscopy techniques. The XRD pattern reveals all samples have tetragonal structures with high crystallinity. The Sn–O stretching vibration has been confirmed through FTIR spectra. The XPS results demonstrate that Sn0.93Ni0.07O2 nanoparticles have Sn3d, Ni2p and O1s oxidation states. EDX spectra contain Ni, Sn and O elements, which indicate the purity of the samples. UV–visible absorption spectrum shows decreases in optical energy bandgap with increases in nickel dopant concentration. The samples exhibit notable antibacterial activity against P. aeruginosa and S. aureus. Also, Sn0.93Ni0.07O2 nanoparticle has higher antifungal activity against A. niger than against C. albicans. Moreover, SnO2 nanoparticles have considerable antioxidant activity in DPPH scavenging compared to Sn0.93Ni0.07O2 nanoparticles. Furthermore, SnO2 nanoparticles have a better cytotoxic effect for L929 normal fibroblast cell lines with an LD50 value of 146.42 μg/mL. Additionally, the photocatalytic activity of SnO2 and Sn0.93Ni0.07O2 nanoparticles was done against methylene blue dye under direct sunlight irradiation. Overall, environmentally friendly synthetic pure and Ni‐doped SnO2 nanoparticles can be used in wastewater filter technologies as well as in medical aids due to their better cytotoxic, antioxidant and antimicrobial effects.

Type-I heterojunction ZnSnO3@PDA/Na0.5Bi0.5TiO3 with PDA as interfacial electron transport bridge for efficient degradation of oxytetracycline and Acid chrome blue K

Type-I heterojunction ZnSnO3@PDA/Na0.5Bi0.5TiO3 with PDA as interfacial electron transport bridge for efficient degradation of oxytetracycline and Acid chrome blue K