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A wide bandgap is one of the major obstacles that hamper the photoelectric application of ferroelectrics. This work reported the tunable band gaps of ferroelectric Aurivillius Bi 3.15 Nd 0.85 Ti 3 O 12 (BNdT) by B-site X (X = Ni, Co, Cr Mn, or Fe) substitution. The analysis of the UV–vis absorption spectra showed a decrease in the band gap induced by substitution and the valence band XPS (VBXPS) spectra indicated that the substitution of X ions elevates the valence band maximum (VBM). The octahedral distortion was estimated qualitatively by Raman analysis and quantitatively through the structural refinements. It is found that the change of the energy band structure and the band gap tuning are proportional to the octahedral distortion induced by B-site substitution. To our knowledge it's the first time to relate the octahedral distortion to the band gap tuning quantitatively for ferroelectric Aurivillius compounds, and the present work will shed light on the mechanism of band gap tuning of ferroelectric oxides materials and provide an available way on manipulating oxide optoelectronics. [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT + U reveals bandgap engineering in CsSnCl 3 with diverse dopants (Ti, V, Cr, Mn). • Favorable modifications of the density of states observed due to doping. • Successful tuning of bandgap, enhances absorbance of visible spectrum. • The ductile nature of doped samples is suitable for the fabrication of thin films. In the realm of advanced electrical and photovoltaic applications, inorganic metal halide perovskites (MHP) have captured attention. However, CsSnCl 3 , a notable member of MHPs, displays limited electro-optical potential due to its substantial bandgap and poor visible spectrum absorbance, which impedes its ability to achieve ideal optoelectronic efficiency. In this study, we used density functional theory (DFT) and the DFT + U technique to compute and investigate the structural, elastic, electrical, and optical properties of pure CsSnCl 3 and its doped phases containing Ti, V, Cr, and Mn with different concentrations. Notably, this study represents the first utilization of DFT + U to simultaneously assess the band structure of both pure and doped CsSnCl 3. Through meticulous alignment with experimental data and the derivation of a suitable Hubbard U correction value (6.5), our analysis reveals a refined band structure for pristine CsSnCl 3. Critically, our research transcends conventional bandgap understanding, unlocking a profound connection between bandgap modulation and enhanced optoelectronic efficiency. Specifically, our systematic exploration uncovers a noteworthy enhancement in performance for various optoelectronic applications upon doping with V, Ti, Cr, and Mn, substantiating the practicality of our approach. Investigations into mechanical stability reveal that all doped samples exhibit a remarkable ductile nature, rendering them well-suited for thin-film solar cell production and other applications demanding stability and flexibility. By bridging the gap between theory and application, our study empowers researchers and industry professionals with actionable insights for selecting the most suitable doped compositions of CsSnCl 3 , ushering in an era of highly efficient and environmentally sustainable optoelectronic technologies. [ABSTRACT FROM AUTHOR]

In this study, we synthesized Cu and Co co-doped ZnO nanoparticles, denoted as Zn 1-2x Cu x Co x O (x = 0.01, 0.02, 0.03), using the sol-gel auto-combustion method. Successful integration of Cu and Co elements into the ZnO host lattice was confirmed through a comprehensive array of spectroscopic techniques. Structural analysis revealed the persistence of a hexagonal wurtzite crystal structure with some distinct microstructural variations across all samples. Alteration in lattice parameters and dislocation density strongly suggests the successful incorporation of Cu2+ and Co2+ ions within the ZnO lattice. A prominent increase in crystallite size from 27.19 nm to 33.46 nm was observed with the increase in doping concentration. Field emission scanning electron microscopy showed a combination of uniformly distributed spherical and hexagon-like structures. Furthermore, UV–Visible absorption spectra demonstrated a proportional enhancement in energy band gap from 2.14 eV for Zn 0.98 Cu 0.01 Co 0.01 O to 2.40 eV for Zn 0.94 Cu 0.03 Co 0.03 O. The Burstein−Moss effect was invoked to elucidate the observed blue shift in absorption spectra and energy band gaps, further solidifying our findings. The systematic and substantial correlation between dopant concentration and energy band gap signifies that the co-doping of Cu and Co is a viable strategy for engineering the band gap of ZnO. This collective investigation unveils the substantial potential of Cu and Co co-doping in ZnO nanoparticles for advanced optoelectronic applications, paving the way for tailored optical and photonic functionalities. • Cu and Co co-doping in ZnO offers potential for tailored optoelectronic applications. • Increasing dopant concentration enlarges crystallite size and widens the energy band gap. • Cu and Co co-doping modifies ZnO's properties, confirmed by spectroscopic analysis. [ABSTRACT FROM AUTHOR]

A family of Ruddlesden–Popper (n = 1) layered perovskite-related phases, Az2PbClxBr4−x with composition 0 ≤ x ≤ 4 were obtained using mechanosynthesis. These compounds are isostructural with K2NiF4 and therefore adopt the idealised n = 1 Ruddlesden–Popper structure. A linear variation in unit cell volume as a function of anion average radius is observed. A tunable bandgap is achieved, ranging from 2.81 to 3.43 eV, and the bandgap varies in a second-order polynomial relationship with the halide composition.

Graphitic carbon nitride (g-C 3 N 4) has attracted increasing interest as a visible-light-active photocatalyst. In this study, saddle-curl-edge-like g-C 3 N 4 nanosheets were prepared using a pellet presser (referred to as g-CN P nanosheets). Urea was used as the precursor for the preparation of g-C 3 N 4. Thermal polymerization of urea in a pellet form significantly affected the properties of g-C 3 N 4. Systematic investigations were performed, and the results for the modified g-C 3 N 4 nanosheets are presented herein. These results were compared with those for pristine g-C 3 N 4 to identify the factors that affected the fundamental properties. X-ray diffraction analysis and high-resolution transmission electron microscopy revealed a crystallinity improvement in the g-CN P nanosheets. Fourier-transform infrared spectroscopy provided clear information regarding the fundamental modes of g-C 3 N 4 , and X-ray photoelectron spectroscopy (XPS) peak-fitting investigations revealed the variations of C and N in detail. The light-harvesting property and separation efficiency of the photogenerated charge carriers were examined via optical absorption and photoluminescence studies. The valence band edge and conduction band edge potentials were calculated using XPS, and the results indicated a significant reduction in the bandgap for the g-CN P nanosheets. The Brunauer–Emmett–Teller surface area increased for the g-CN P nanosheets. The photocatalytic degradation performance of the g-CN P nanosheets was tested by applying a potential and using the classical dye Rhodamine B (RhB). The RhB dye solution was almost completely degraded within 28 min. The rate constant of the g-CN P nanosheets was increased by a factor of 3.8 compared with the pristine g-C 3 N 4 nanosheets. The high crystallinity, enhanced light absorption, reduced bandgap, and increased surface area of the saddle-curl-edge-like morphology boosted the photocatalytic performance of the g-CN P nanosheets. [ABSTRACT FROM AUTHOR]

Nitrogen‐doped BaTiO3 (BT) ceramics were produced by the solid‐state reaction method in conjunction with ammonia gas treatment. The optical absorption spectra results show that the bandgap of BT ceramic is narrowed after N‐doping, suggesting that the N‐doping is an effective route to increase light absorption. Polar properties measurements indicate that the ferroelectricity of BT ceramic is well maintained after the N‐doping. In addition, the electric‐field–induced strain is prominently improved to ~0.8% after N‐doping, a value superior to that of PZT. Furthermore, the influence of N‐doping on photoelectric properties of BT ceramics was also investigated. Large increase in photoconductivity and fast response to light illumination conditions were observed in N‐doped BT ceramics. This work provides a novel route to enhance the (photo)electric properties of ferroelectric materials. [ABSTRACT FROM AUTHOR]

Abstract The newly found graphene-like material C 3 N exhibits great potential in a variety of important applications, due to its unique topological and electronic structures. To extend the utilization, a crucial challenge is to make its intrinsic bandgap (1.03 eV) tunable. Here we performed first-principles calculations to investigate the band structure variations of C 3 N monolayer under various surface modification treatments, including defect engineering, surface decoration and substitutional doping. Results show that those treatments can induce impurity states, orbital rehybridization, and n- or p-type doping simultaneously, and therefore enable effective band structure adjustment. Importantly, some linear relationships between the bandgap and doping concentration are revealed, paving the way for precise control of C 3 N bandgap. [ABSTRACT FROM AUTHOR]

Tunable electronic properties of two dimensional Molybdenum disulfide (MoS _2 ) make it a potential material. In this study, we inspect electronic and structural properties of TMN-doped MoS _2 (T = Transition metal (Cu-copper), M = Metalloid (B-boron) and N = Nonmetal (C-carbon)) by using first principles DFT (density functional theory) calculations. Cu is substituted by Mo with varying concentration, which ranges from 2.08 to 8.33%, whereas B and C are replaced by S atoms with varying concentration of 2.08 to 4.16%. The substitutions result into significant variations in electronic and structural properties of MoS _2 . Moreover, the importance of substitutional site has been elaborated. The substitution of these impurities, variation in concentration and the replaced sites of MoS _2 cause to modify the structure and energy gaps. Resulting bandgap fluctuates remain between 0.16 eV to 0.48 eV relative to 1.95 eV of pristine MoS _2 . The PDOS calculations show good bonding relation among the host MoS _2 and the foreign impurity TMN. Therefore, substitution of impurities gives the opportunity to vary the bandgap as required for its valuable applications as semiconducting materials.

Ternary alloys of Zn 0.78 Cd 0.22 S nanoparticles (NPs) are synthesized via the facile co-precipitation technique. The as-synthesized sample exhibits a zincblende-type cubic phase with an average crystalline size of 2 nm. Thermal annealing and UV irradiation are utilized as post-treatment processes for tailoring the optical properties of Zn 0.78 Cd 0.22 S NPs. The as-synthesized sample exhibits a stable cubic phase up to 400 °C, during which partial phase transformation to a hexagonal structure is observed at a higher temperature of 500 °C. The oxidation of Zn 0.78 Cd 0.22 S NPs to mixed oxide phases with the majority of ZnO begins at 600 °C which induces morphology transformation to a relatively large nano-hexagon with a single crystalline domain size. The increase of the annealing temperature is accompanied by a decrease of Zn 0.78 Cd 0.22 S NPs optical band gap (E g) due to the weakness of size confinement as well as the formation of localized states below the mobility band edges. The brief UV irradiation results in the increase of E g whereas a further increase in exposure time is accompanied by a reduction of E g. The photoluminescence (PL) spectrum of the as-synthesized sample covers a wide spectral range from UV to visible. Thermal annealing has a slight effect on the PL emission at high excitation energy, whereas low excitation energy reveals higher sensitivity to deep-state emission. Thermal oxidation incorporates a high concentration of oxygen-related defects that induce strong enhancement in the green emission at the expense of UV emission. This indicates the thermal-induced bleaching of shallow trapping sites and the evolution of other deep trapping or recombination sites. • Homogeneous Zn 0.78 Cd 0.22 S nano-alloys are synthesized via a co-precipitation technique. • Thermal annealing results in the morphological transformation from nanoparticle to large nano-hexagon. • Thermal annealing results in a dramatic increase in the green emission intensity. • Photoluminescence of Zn 0.78 Cd 0.22 S NPs exhibits dependence on excitation energy. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrothermal technique was utilized to fabricate yttrium doped ZnO nanorods. • The bandgap of the ZnO nanorods was significantly altered by doping yttrium. • The Y-doped ZnO nanorods degraded 97 % of MB dye under visible-light. • Super oxide radicals and holes play a dominant role in the degradation of MB. The hydrothermal technique was utilized to fabricate yttrium doped ZnO nanorods (Y-doped ZnO). Various spectroscopic approaches were used to examine the effect of yttrium doping on the crystal structure, shape, energy bandgap, and photocatalytic performance of ZnO nanorods. The fact that Y-doped ZnO nanocatalysts had the same hexagonal wurtzite crystal structure and nanorod shape as like undoped ZnO, signifying that doped yttrium ions have no effect on the structural as well as morphological features of ZnO nanorods. By doping yttrium into the ZnO sites, the bandgap energy of the ZnO nanorods was significantly altered, and the photodegradation activity was improved. The absorption edge of the Y-doped ZnO nanorods was shifted towards the higher wavelengths and blue shift in bandgap was observed. It has been confirmed that yttrium doping increases the light sensitivity of ZnO in the visible region while providing several active charge transporters on the nanorods surface as well. The photocatalytic activity of Y-doped ZnO nanocatalysts was significantly increased by generated charge carriers. For doping concentrations of 1 %, 3 % and 5 %, the photodegradation activity of Y-doped ZnO nanorods is 71 %, 97 %, and 82 %, respectively, whereas the photodegradation efficiency of pure ZnO nanorods is 22 %. The photodegradation efficiency of ZnO:Y3 was found to be 4.4 times higher than the pristine ZnO nanorods. In addition to the photodegradation, the Y-doped ZnO nanorods are anticipated to offer a valued platform to the widespread applications in the field of photocatalysis like electrochemical water splitting, hydrogen production and supercapacitors. [ABSTRACT FROM AUTHOR]

Heteroatom-doping is an efficient approach to extend optical absorption beyond 460 nm, which, however, often reduces crystallinity to cause a concomitant detrimental effect on photocatalytic activity. In the present study, we developed a facile approach to synthesize S-doped g-C 3 N 4 with a high crystallinity by self-assembling melamine and tri-thiocyanuric acid, followed by calcination. The resultant optimal S-doped carbon nitride (MTCN-6) exhibited a super-high H 2 -generation rate of 1511.2 μmol g −1  h -1 (about 11 times higher than that of the pristine CN) under visible light excitation (λ > 420 nm) and an excellent AQE of 3.9% at 420 nm. [ABSTRACT FROM AUTHOR]

Abstract In the present study, we have elucidated an effective way to simultaneously tune the optical bandgap and magnetic properties of zinc oxide (ZnO) thin films. This can be achieved by the incorporation of nitrogen ions in the host matrix. We have systematically investigated the influence of N ions in ZnO thin films through experimental techniques and the density functional theory (DFT) calculations to understand the physical mechanism governing the observed magnetic behaviour and the variation in bandgap. For this, RF sputtered ZnO thin films deposited over Si substrates were implanted with N ions by varying the fluences and studied for their optical and magnetic properties. The pristine ZnO film is having saturation magnetization of ∼2.45 emu/cm3 which becomes almost twice for the ion fluence of 1 × 1017 ions/cm2. Furthermore, the optical bandgap is tuned from 3.27 eV to 3.04 eV with N ion implantations. This study provides a new insight to understand the basis of ferromagnetism in non-magnetic ions doped ZnO system. Highlights • Influence of N implantation on optical and magnetic properties of ZnO thin films. • Experimental & DFT calculations have been performed to understand the mechanism. • Increase in saturation magnetization with N ion implantations. • Decrease in optical bandgap with increasing N concentration. [ABSTRACT FROM AUTHOR]

Abstract: Here, unbiased water splitting with 2% solar‐to‐hydrogen efficiency under AM 1.5 G illumination using new materials based on GaSb0.03P0.97 alloy is reported. Freestanding GaSbxP1−x is grown using halide vapor phase epitaxy. The native conductivity type of the alloy is modified by silicon doping, resulting in an open‐circuit potential (OCP) of 750 mV, photocurrents of 7 mA cm−2 at 10 sun illumination, and corrosion resistance in an aqueous acidic environment. Alloying GaP with Sb at 3 at% improves the absorption of high‐energy photons above 2.68 eV compared to pure GaP material. Electrochemical Impedance Spectroscopy and illuminated OCP measurements show that the conduction band of GaSbxP1−x is at −0.55 V versus RHE irrespective of the Sb concentration, while photocurrent spectroscopy indicates that only radiation with photon energies greater than 2.68 eV generate mobile and extractable charges, thus suggesting that the higher‐laying conduction bands in the Γ 1 valley of the alloys are responsible for exciton generation. [ABSTRACT FROM AUTHOR]

Narrow bandgap and its tuning are important aspects of materials for their technological applications. In this context group IV{VI semiconductors are one of the interesting candidates. In this paper, we explore the possibility of bandgap tuning in one of the family member of this family GeSe by using isoelectronic Pb doping. Our study is first-principles based electronic structure calculations of Ge1-xPbxSe. This study reveals that the Ge-p and Se-p states are strongly hybridized in GeSe and shows a gap in the DOS at Ef in GeSe. This gap reduces systematically with simultaneous enhancement of the states in the near Ef region as a function of Pb doping. This leads tuning of the indirect bandgap in GeSe via Pb doping. The results of the indirect bandgap decrement are consistent with the experimental findings. We propose a mechanism where the electrostatic effect of dopant Pb cation could be responsible for these changes in the electronic structure of GeSe. [ABSTRACT FROM AUTHOR]

Inorganic pigment with NIR reflectance properties could mitigate the energy consumption used for controlling the indoor temperature in buildings. This work presents an environmentally benign pigment series of Bi3+ and V5+ doped CePO 4 of formula Ce 1-x Bi x P 1-y V y O 4 (x = y = 0.02 to 0.5) by coprecipitation and hydrothermal methods. Doping of metal ion could tune the band gap of CePO 4 approximately from 3.01 to 2.4 eV mainly due to the introduction of additional V 3d orbital in the conduction band. Doping changed the color of the compound from white to yellow color. The synthesized compounds were characterized by XRD for phase identification, FT-IR for functional group analysis, UV-DRS to determine the sample's reflectance and band gap, CIE – L*a*b* for color values and SEM techniques for morphology studies. XPS analysis was conducted to confirm the oxidation state of Ce, V and Bi in the compound. Among the series of individual and co-doped CePO 4 series, the compound Ce 0.8 Bi 0.2 (P 0.8 V 0.2 O 4) synthesized from the precipitation method exhibited a high yellow value (b* = 24.58) with single-phased monoclinic system and 75.05% NIR solar reflectance. The same compound prepared by the hydrothermal method exhibited less yellow value (b* = 18.96) and 75.67% NIR solar reflectance. Good chemical stability in acid and alkaline medium was observed. [Display omitted] • V5+ and Bi3+ doped CePO 4 pigments was prepared by two different methods. • Bismuth and vanadium codoped CePO 4 by precipitation method gave b* = 24.58 (R = 75.05%). • Bismuth and vanadium codoped CePO 4 by hydrothermal method have b* = 18.96 (R = 75.67%). • Prepared pigments have the potential to be used in cool coating applications. [ABSTRACT FROM AUTHOR]

Structural, electronic and vibrational spectroscopic investigations were performed for the solid solution NaP7-xAsx up to x = 3.5 featuring a helical polypnictide substructure. Depending on the As content the LiP7 (for x = 0 to 0.8 and 2.5 to 3.5) or KP15 (x = 1.0 to 2.4) structure type is realized up to an maximum As content of x = 3.5. The crystal structures of two selected phases were determined and the distribution of As in the polyanionic substructure was determined. The full solid solution up to x = 7 was subject to a quantum chemical DFT analysis in order to get insights into the stabilities and phase formation tendencies. Van der Waals interactions between the structure subunits were estimated and first principle investigations towards a delamination and nano structuring of NaP7-xAsx crystals into one-dimensional semiconductors were performeda [ABSTRACT FROM AUTHOR]

Significant enhancement in the luminescence and superior photophysical properties of CH3NH3PbBr3 thin films prepared via simple single step spin coating process involving a novel additive mediated solvent extraction step is reported. This process results in significantly lower disorder in CH3NH3PbBr3 perovskites with Urbach energies reducing from ≈35 to ≈17 meV, which is the lowest reported value to date. The additive mediated process also results in a remarkable improvement in the photoluminescence quantum yields (PLQYs) from 1% to 30%. Coupled with the overall increase in surface roughness, a significant increase in the internal PLQY from 7% to 77% is estimated, indicating the superior quality of the treated thin films. The resultant high quality CH3NH3PbBr3 perovskites with remarkable photophysical properties can be used in realizing highly efficient optoelectronic devices. Highly efficient light emitting diodes using these perovskites are demonstrated here. [ABSTRACT FROM AUTHOR]

A study on crystalline silver indium tin oxide (AISO), a quaternary compound formed by tin incorporation in delafossite AgInO 2 is briefed here. X-ray diffraction for structural characterization combined with energy dispersive analysis of X-rays for composition assessment confirms the formation of crystalline thin films with the rhomb-centered rhombohedral delafossite crystalline lattice. The variation in electrical conductivity (10 1 –10 2 S/cm) and activation energy are correlated with carrier concentration and c-axis orientation induced by stoichiometric changes. A band gap tuning from 2.38 eV to 3.23 eV is achieved by the stoichiometry changes. [ABSTRACT FROM AUTHOR]

The authors study adjustable bandgap properties of the novel triple chalcogenophene-based polymer poly-(3-hexyl-2(3-(4-hexylthiophene-2-yl)-4,5-butylselenophene-1-yl)-5-(4,5-butyltellurophene-1-yl)thiophene) through a combination of morphological, spectroscopic, and computational techniques. The bandgap can be tuned after polymerization by means of mild temperature annealing, which will allow for a partnership with a broader range of donor/acceptor molecules, a property that makes it potentially suitable for organic photovoltaic implementation. The bandgap is modified by selection of the annealing temperatures, and the process is arguably related to the aggregation of tellurophene units, as similar effects are observed in polytellurophenes. Moreover, adequate chemistry engineering ensures easy solution processability and attainment of homogeneous films, which is also essential for applications. [ABSTRACT FROM AUTHOR]

Here we report on the Ga self-catalyzed growth of near full-composition-range energy-gap-tunable GaAs1-xSbx nanowires by molecular-beam epitaxy. GaAs1-xSbx nanowires with different Sb content are systematically grown by tuning the Sb and As fluxes, and the As background. We find that GaAs1-xSbx nanowires with low Sb content can be grown directly on Si(111) substrates (0 ≤ x ≤ 0.60) and GaAs nanowire stems (0 ≤ x ≤ 0.50) by tuning the Sb and As fluxes. To obtain GaAs1-xSbx nanowires with x ranging from 0.60 to 0.93, we grow the GaAs1-xSbx nanowires on GaAs nanowire stems by tuning the As background. Photoluminescence measurements confirm that the emission wavelength of the GaAs1-xSbx nanowires is tunable from 844 nm (GaAs) to 1760 nm (GaAs0.07Sb0.93). High-resolution transmission electron microscopy images show that the grown GaAs1-xSbx nanowires have pure zinc-blende crystal structure. Room-temperature Raman spectra reveal a redshift of the optical phonons in the GaAs1-xSbx nanowires with x increasing from 0 to 0.93. Field-effect transistors based on individual GaAs1-xSbx nanowires are fabricated, and rectifying behavior is observed in devices with low Sb content, which disappears in devices with high Sb content. The successful growth of high-quality GaAs1-xSbx nanowires with near full-range bandgap tuning may speed up the development of high-performance nanowire devices based on such ternaries. [ABSTRACT FROM AUTHOR]

Tailoring optical bandgap of ZnO nanostructured thin films doped with different elements facilitates potential material for photonic applications. Different methods of fabrication process result in different optical and structural properties for the same amount of Mg content. Therefore, details investigation of structural and optical parameters, and their correlation need to be revealed to utilize the fabricated thin films. In this work, Mg-doped ZnO thin film of 200 nm thickness was fabricated by sol-gel spin coating method on a glass substrate for four different Mg content levels. Multiple layers were deposited by a spin coater to increase the film thickness. The prepared thin films were characterized by SEM, XRD, EDS, and UV–Vis spectroscopy. The spectroscopic analysis showed a uniform crystalline nanostructured surface with less structural defects, enhanced transmittance, and higher optical bandgap than that of pure ZnO nanostructured thin film. Change of Mg content from 2% to 8% facilitated tuning of bandgap in the range of 3.30–3.39 eV. Changing trend of structural and optical parameters with Mg content showed non-linear, non-monotonic relation. In-depth analysis of structural and optical properties provides crucial information to form a better view about bandgap dependency on structural parameters. [ABSTRACT FROM AUTHOR]

The future hydrogen economy urges to replace platinum-based catalysts since large-scale production of hydrogen using platinum is not economically viable to deal with the influx of interest. Developing cost-effective, durable, and efficient catalysts is one of the most relevant research frontiers. Herein, interconnected and { 10 1 ̅ 0 } faceted 2D zinc oxide decorated on graphene sheets was effectively fabricated by a simple CTAB-assisted microwave technique and has been intensively investigated for photocatalytic dye degradation and electrocatalytic hydrogen evolution. The XRD and Raman spectra confirm the in-situ reduction of GO to rGO and successful synthesis of ZnO/rGO hybrids. Compared with the pure ZnO, as-obtained ZnO/rGO hybrids exhibited good stability and superior photocatalytic efficiency under visible-light irradiation, owing to reduced electron-hole pair recombination upon GO incorporation, as affirmed by PL spectra, TRPL lifetime measurements, and photocurrent responses. The 2D/2D ZnO/rGO hybrid nanostructure showed optimised material properties for exceptional electrochemical H 2 evolution, producing a current density of − 10 mA/cm2 at a significantly reduced overpotential of − 810 mV vs. RHE, and a Tafel slope of 157 mV/dec in 0.5 M H 2 SO 4. The enhanced catalytic activity can be attributed to the introduction of rGO sheets, which improved the surface area and electrical conductivity of the sample. The multifunctional nature of ZnO/rGO hybrids in both photocatalysis and electrocatalysis sheds light upon environmental pollution and the energy crisis. [Display omitted] • { 10 1 ̅ 0 } faceted ZnO/graphene 2D/2D nanostructures are prepared by simple one step microwave method in a short time. • Interconnected ZnO are immobilized uniformly on the surface of rGO nanosheets. • An extended visible light absorption and enhanced charge carrier separation is achieved by ZnO/rGO hybrid. • ZnO with 0.5 wt% of GO shows excellent visible light photocatalytic activity. • ZG0.5 also exhibits good electrocatalytic HER performance. [ABSTRACT FROM AUTHOR]

Negative-stiffness mechanical metamaterials that can achieve bandgap tuning are a novel area of intense interest, enabling vibration control as well as a wide range of mechanical properties. In this paper, a negative-stiffness mechanical metamaterial consists of beam elements that can be reconfigured for large deformations and the bandgap can be tuned by its deformation behavior. The deformation process of the proposed negative-stiffness metamaterial under uniaxial compression, as well as the band structure and vibration characteristics of the metamaterial under different deformation states are analyzed by a combination of numerical simulation and experiment. The research results show that the proposed negative-stiffness metamaterial suffers from buckling instability and large deformation during uniaxial compression., and has different band structures and band gap ranges under different deformation states. Thus, bandgap tuning can be achieved by the deformation of negative stiffness metamaterials. Furthermore, negative stiffness metamaterials with different angles exhibit different results in bandgap tuning. Finally, the performance of vibration transfer is verified by experiments. This study may provide a new avenue for the related research and design of negative-stiffness mechanical metamaterials with bandgap tuning capabilities. [ABSTRACT FROM AUTHOR]

Here we present a simple and effective way of bandgap tuning by V-substitution in TiO 2 . The nanoparticles of Ti (1-x) V x O 2 (for 0≤ x ≤0.09) were prepared by controlled and simplified sol-gel method. The pure anatase phase of TiO 2 was confirmed by X-ray diffraction and Raman spectroscopy. Debye-scherrer formula and Williamson-Hall plot give crystallite size decreases from 10.8 to 8.2 nm when strain increases from 0.019 to 0.027 for x =0 to x =0.09. Rietveld refinement show the systematic change in crystal structure with the amount of V-substitutions. Raman shift and broadening of FWHM of first E g (145.52 cm −1 ) mode observed in Raman spectroscopy follow interestingly the similar and correlated observation with XRD outcomes. FESEM and UHRTEM represent pictorial view of the morphology of the nanoparticles with information about different micro-agglomerations and crystallinity. The oxidation states and local environment of elements in nanoparticles were studied using XANES. V-substitution in TiO 2 shows band gap moderation: band gap decreases gradually with substitution from 3.06–2.02 eV as concentration of V increases from x =0.0 to 0.09. This extends the application of TiO 2 in UV as well as visible light whereas the application of pure TiO 2 is limited in only UV region. The results of SEM, XRD, Raman spectroscopy and UV-vis spectroscopy are correlated well with lattice distortion and the lattice distortion gives the Urbach energy. We reach to the conclusion that the effective bandgap decreases may be due to creation of impurity energy levels or Urbach energy tails just above valance band and below conduction band. [ABSTRACT FROM AUTHOR]

Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V1-yVy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux. [ABSTRACT FROM AUTHOR]

The structural, electronic, optical, and photocatalytic properties of 2D Y 2 CF 2 and Lu 2 CF 2 MXenes are investigated by density functional theory approach. According to the obtained results, 2D Y 2 CF 2 and Lu 2 CF 2 are indirect bandgap semiconductors of ~1.67 eV and ~1.42 eV, respectively. The indirect-to-direct bandgap transition was observed at the tensile strain of 8% (12%) for Y 2 CF 2 (Lu 2 CF 2). It is worth noting that the dynamical stability of these structures was confirmed. The optical properties including complex dielectric function, absorption, reflectivity and energy loss function of these MXenes are also studied in both unstrained and strained states. The obtained results reveal the good absorption of these monolayers in the visible and ultraviolet ranges. Furthermore, based on the photocatalytic properties, Y 2 CF 2 and Lu 2 CF 2 MXenes can be used for O 2 /H 2 O water splitting half-reaction, keeping this behavior under applied strain. Additionally, according to the band alignments of these materials with respect to that of g-C 3 N 4 , a Z-scheme Y 2 CF 2 or Lu 2 CF 2 /g-C 3 N 4 heterojunction can be considered to increase the CO 2 photocatalytic reaction under solar light irradiation. All obtained results exhibit that M 2 CF 2 (M=Y, Lu) monolayers are promising candidates for optoelectronic, solar energy and photocatalytic applications. • The strain effects on structural, electronic, optical and photocatalytic properties of 2D Y 2 CF 2 and Lu 2 CF 2 MXenes are investigated. • The transition from indirect to direct bandgap occurred in the tensile strain of 8% (12%) for 2D Y 2 CF 2 (Lu 2 CF 2). • Y 2 CF 2 and Lu 2 CF 2 have potential application as photocatalyst for O 2 /H 2 O water splitting half-reaction. • The Z-scheme Y 2 CF 2 or Lu 2 CF 2 /g-C 3 N 4 heterojunction can be a proper candidate to increase the CO 2 photocatalytic reaction. [ABSTRACT FROM AUTHOR]

• Van der Waals heterostructures can be used in atomically thin solar cells. • Van der Waals heterostructure solar cells have enhanced light absorption. • The bandgap can be tuned in the van der Waals heterostructure solar cells. • Van der Waals heterostructure solar cells use a few amounts of the materials. • Van der Waals heterostructure solar cells could approach to high conversion efficiencies. The emergence of 2D materials in recent years has led to the designing of new novel structures that take advantage of the van der Waals forces in the stacking of dissimilar 2D layers on each other. These structures are called van der Waals heterostructures (vdWHs). The vdWHs have been used in several electronic and optoelectronic applications, including photovoltaic devices and solar cells. Application of 2D semiconductor materials in vdWHs allows bandgap tunning and longer exciton lifetimes. The vdWHs solar cells benefit from high conversion efficiencies, enhanced light absorption, and application of a small amount of the active materials due to their atomically thin structure. The inter-layer exciton in the vdWHs has a longer lifetime than individual layers. The thickness of the inserting insulating interlayer can modulate the binding energy strength of the interlayer exciton. This review studies different types of photovoltaic and solar cells devices working based on the vdWHs. The challenges and prospects for developing this type of solar cell have been addressed. [ABSTRACT FROM AUTHOR]

Herein, the synthesis of Cu 3 (HAB) x (TATHB) 2-x (HAB: hexaaminobenzene, TATHB: triaminotrihydroxybenzene) is reported. Synthetic improvement of Cu 3 (TATHB) 2 leads to a more crystalline framework with higher electrical conductivity value than previously reported. The improved crystallinity and analogous structure between TATHB and HAB enable the synthesis of Cu 3 (HAB) x (TATHB) 2-x with ligand compositions precisely controlled by precursor ratios. The electrical conductivity is tuned from 4.2 × 10 -8 to 2.9 × 10 -5  S cm -1 by simply increasing the nitrogen content in the crystal lattice. Furthermore, computational calculation supports that the solid solution facilitates the band structure tuning. It is envisioned that the findings not only shed light on the ligand-dependent structure-property relationship but create new prospects in synthesizing multicomponent electrically conductive metal-organic frameworks (MOFs) for tailoring optoelectronic device applications., (© 2023 Wiley-VCH GmbH.)

Lead-based all-inorganic metal halide perovskites are of current interest due to their novel properties and potential applications in optoelectronic devices. Controllably strain and mixed-halide compositions are valuable way of tuning the bandgap and improve optoelectronic properties. Here, structure stability, mechanical and optoelectronic properties of strain-tuned mixed-halide CsPbX 3-a Y a (X, Y =I, Br, Cl; a = 0, 1, 2, 3) are investigated by first-principles calculations. Results show that their structural stability were improved with the increasing of Br or Cl doping concentration. Elastic calculations indicates that these mixed-halide CsPbX 3-a Y a (X, Y =I, Br, Cl; a = 0, 1, 2, 3) compounds are all mechanically stable and possess superior ductility in the studied range of pressure, which makes them suitable for thin films and flexible solar cells. Moreover, the ductility becomes more excellent as the pressure increases. Electronic properties calculations exhibit that these compounds have similar band structure. That is, they are all direct bandgap semiconductors, and the energy gap decreases with increasing pressure, and finally all structures are transformed into metallic phase. Based on the electronic structure, the optical absorption coefficients are calculated, which show that the main absorption region shifts to red light and the absorption capacity enhancement with the increase of pressure, but decreases with the increase of doping concentration of Br or Cl doping. • The structural stability of CsPbX 3-a Y a were improved with the increasing of Br or Cl doping concentration. • The CsPbX 3-a Y a (X, Y =I, Br, Cl; a = 0, 1, 2, 3) are all mechanically stable and possess superior ductility under pressure. • The energy gap decreases with increasing pressure, and finally all structures were transformed into metallic phase. • Strain-tuned optical properties in perovskites CsPbX 3-a Y a were studied systematically. [ABSTRACT FROM AUTHOR]

Al-doped CuInSe2 material is prepared by a low-cost wet chemical process. The key properties of Al-doped CuInSe2 as a successful solar cell material are investigated, such as crystal structure, morphology, optical properties, and bandgap. In situ X-ray diffraction measurements indicate that the doping of Al has induced noticeable lattice distortion. The material shows excellent thermal stability up to 600 °C annealing temperature. By increasing the Al-doping concentration, the crystal unit-cell parameter of the material becomes smaller and the change of crystal structure leads to an increase of the grain size and surface roughness. The bandgap of Al-doped CuInSe2 can be continuously tuned in a range of 1.07-1.67 eV as Al/(Al + In) content ratio varies from 0 to 0.49. Finally, the effect mechanism on the properties of CuInSe2 after Al doping is discussed based on the ionic radius, crystal structure, and bonding state. [ABSTRACT FROM AUTHOR]

In contemporary years, hybrid lead halide perovskites nanocrystals (HPNCs) have emerged as core materials for low-cost solution-processable photovoltaic, light-emitting devices as well as in other optoelectronic fields, such as high-efficiency perovskite fluorescent quantum dots (quantum dot, QD). Although the high efficiency makes them an attractive active material, reducing the Pb-toxicity and enhancing the stability while sustaining the efficiency of the HPNCs devices is important for their successful commercialization in future. Here, we report for the first time the fabrication of excellent quality Pb-less, MAPb 1- x Sn x Br 3 ( x  = 0 to 0.50) perovskite NCs by one-pot ultrasonication method. Interestingly, an outstanding photoluminescence quantum yield (PLQY) of 94% and better lifetime performance than 100% Pb-based HPNCs is obtained for Pb-less HPNCs. The successful incorporation of Sn MAPb 1- x Sn x Br 3 HPNCs is confirmed by energy-dispersive x-ray (EDX) and x-ray photoelectron spectroscopy (XPS) analysis. Although the particle size for Pb-less HPNCs was different, the change in morphology and structure was minimal as confirmed by transmission electron microscopy (TEM) analysis. The optical analysis indicated bandgap tuning, which is evident by the blue shift of the band edge in absorbance spectra and photoluminescence peak after incorporating Sn 2+ . To the best of our knowledge, this is the highest achieved PLQY for Sn-substituted hybrid Pb-based HPNCs. The synthesis by using one pot ultrasonication method might be helpful for large-scale HPNCs production and can pave the way for future research on less-toxic and stable alternatives to Pb-based HPNCs., (© 2022 IOP Publishing Ltd.)

[Display omitted] • The non-stoichiometric amorphous Ga 2 O 3-x thin films are crystallized into a mixture of α and β phases that are epitaxial to the sapphire (0001) substrate. • The non-stoichiometric state of the Ga 2 O 3-x thin films is composed of metallic Ga, Ga 2 O, and Ga 2 O 3. • Ga and Ga 2 O are oxidized into Ga 2 O 3 , achieving a stoichiometric state during the post-annealing process in an atmospheric environment. • The optical bandgap gradually increases from 4.16 eV for the as-grown sample to 4.81 eV for the sample annealed at 600 ℃. The evolution of the structural and chemical properties of non-stoichiometric amorphous Ga 2 O 3-x thin films during post-annealing in an atmospheric environment was investigated using scanning electron microscopy, X-ray diffraction, ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and ultraviolet–visible light spectroscopy. The amorphous thin films were crystallized into a mixture of α and β phases that were epitaxial to the sapphire (0001) substrate. The AP-XPS results indicate that the non-stoichiometric state of the Ga 2 O 3-x thin films is composed of metallic Ga, Ga 2 O, and Ga 2 O 3. Ga and Ga 2 O are oxidized into Ga 2 O 3 , achieving a stoichiometric state during the post-annealing process. This gradually increases the optical bandgap from 4.16 eV for the as-grown sample to 4.81 eV for the sample annealed at 600 ℃. Our results support the relationship between the chemical composition and bandgap of non-stoichiometric Ga 2 O 3-x films deposited by radio-frequency powder sputtering. [ABSTRACT FROM AUTHOR]

ZnO thin films doped with different Cu concentrations are fabricated by reactive magnetron sputtering technique. XRD analysis indicates that the crystal quality of the ZnO:Cu film can be enhanced by a moderate level of Cu-doping in the sputtering process. The results of XPS spectra of zinc, oxygen, and copper elements show that Cu-doping has an evident and complicated effect on the chemical state of oxygen, but little effect on those of zinc and copper. Interestingly, further investigation of the optical properties of ZnO:Cu samples shows that the transmittance spectra exhibit both red shift and blue shift with the increase of Cu doping, in contrast to the simple monotonic behavior of the Burstein--Moss effect. Analysis reveals that this is due to the competition between oxygen vacancies and intrinsic and surface states of oxygen in the sample. Our result may suggest an effective way of tuning the bandgap of ZnO samples. [ABSTRACT FROM AUTHOR]

The energy gap between valence and conduction levels in colloidal semiconductor quantum dots can be tuned via the nanoparticle diameter when this is comparable to or less than the Bohr radius. In materials such as cadmium mercury telluride, which readily forms a single phase ternary alloy, this quantum confinement tuning can also be augmented by compositional tuning, which brings a further degree of freedom in the bandgap engineering. Here it is shown that compositional control of 2.3 nm diameter Cd xHg(1− x)Te nanocrystals by exchange of Hg2+ in place of Cd2+ ions can be used to tune their optical properties across a technologically useful range, from 500 nm to almost 1200 nm. Data on composition-dependent changes in the optical properties are provided, including bandgap, extinction coefficient, emission energy and spectral shape, Stokes shift, quantum efficiency, and radiative lifetimes as the exchange process occurs, which are highly relevant for those seeking to use these technologically important QD materials. [ABSTRACT FROM AUTHOR]

Extending a key observation made by Meyers et al. (Meyers et al., J Chem Phys, 1992, 97, 2750), a strategy for the systematic design of conducting polymers with tailor-made bandgaps and carrier effective masses is described and quantum-chemically implemented. Such strategy relies on the construction of alternating binary copolymers from well-characterized parent polymers, in such a manner that those electronic parameters can be phenomenologically predicted from the composition of the copolymer. Illustrative calculations for three types of alternating copolymers built from five parent π-conjugated polymers demonstrate the plausibility of the methodology and the internal consistency of its computational implementation. Specifically, it is shown that the bandgaps of copolymers built from parent monomers with similar chemical structures exhibit nearly linear behaviors as functions of composition, whereas the bandgaps of copolymers with dissimilar parent monomers exhibit nearly monotonic deviations from linearity. On the other hand, the electron and hole effective masses of copolymers with similar parent monomers do not show a significant dependence on composition, whereas for copolymers with dissimilar parent monomers these quantities also display nearly monotonic deviations from linearity. A qualitative rationalization of these trends in terms of the strengths of the inter-parent–monomer interactions, which bears an intriguing resemblance to the behavior of the vapor pressure of binary solutions, is provided. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: CuIn1− x Ga x Se2 (CIGS) solar cells show a good spectral response in a wide range of the solar spectrum and the bandgap of CIGS can be adjusted from 1.0 eV to 1.7 eV by increasing the gallium-to-indium ratio of the absorber. While the bandgaps of Ga-rich CIGS or CGS devices make them suitable for top or intermediate cells, the In rich CIGS or CIS devices are well suited to be used as bottom cells in tandem solar cells. The photocurrent can be adapted to the desired value for current matching in tandem cells by changing the composition of CIGS which influences the absorption characteristics. Therefore, CIGS layers with different [Ga]/[In+Ga] ratios were grown on Mo and ZnO:Al coated glass substrates. The grain size, composition of the layers, and morphology strongly depend on the Ga content. Layers with Ga rich composition exhibit smaller grain size and poor photovoltaic performance. The current densities of CIGS solar cells on ZnO:Al/glass varied from 29 mA cm−2 to 13 mA cm−2 depending on the Ga content, and 13.5% efficient cells were achieved using a low temperature process (450 °C). However, Ga-rich solar cells exhibit lower transmission than dye sensitized solar cells (DSC). Prospects of tandem solar cells combining a DSC with CIGS are presented. [Copyright &y& Elsevier]

This numerical study deals with the CIGS solar cell considering Cd 1-x Zn x S buffer layer. The composition 'x' of the buffer layer is determined and its impact on the solar cell performance parameters is studied. The influence of the buffer layer thickness on quantum efficiency is also discussed. The tuned bandgap and optimized thickness of the Cd 1-x Zn x S buffer layer are then utilized to obtain the suitable bandgap of the CIGS absorber layer. The maximum power conversion zone is revealed in terms of the CIGS bandgap and the impact of this bandgap on spectral response as well as performance parameters are discussed. The Cd 0.6 Zn 0.4 S/CIGS interface is studied by varying the defect density from 1010 cm−3 to 1016 cm−3. The cell performances are also analyzed for the temperature ranging from 260 K to 350 K. • The optimized concentration of Zn in Cd 1-x Zn x S buffer is 0.4 corresponding to the bandgap of 2.83 eV. • For a 50 nm thin Cd 0.6 Zn 0.4 S buffer layer, highest QE is achieved. • The proposed cell structure exhibits an efficiency of 26.02% for CIGS bandgap of 1.4 eV. • The cell performance degrades with the increase of InCd 0.6 Zn 0.4 S/CIGS interface defect density and temperature. [ABSTRACT FROM AUTHOR]

Here, a hierarchical Ni x Mn (0.5−x) O catalyst that propels charge carriers to opposite interfaces of core@shell nanoparticle is reported. The opposite drift of charge carriers was achieved by tuning band edges in a multilevel catalyst by varying the molar concentration (x, 0→0.5) of precursors in a series of input injections. Preferential oxidation by holes on the surface of the catalyst was confirmed with the oxidation state transformation of metal ions (platinum and lead) deposited on the catalyst from their respective solutions. To obtain an electron rich surface, the synthesis scheme was reversed (x, 0.5→0), which yielded a catalyst with an inverse geometry and directed electron flow towards the surface. The collective impact of the Lorentz force and internal charge carrier drift contributed to excellent recombination suppression and 98% sulfamethoxazole degradation in 30 min. Finally, structural integrity and catalytic potential of the composite after repeated magnetic separation and degradation cycles was assessed to establish its practical applicability. [Display omitted] • Band edges were tuned in magnetically separable catalyst by in–situ precursor injections. • Band edge tuning sets an energy field that promotes directional flow of charge carriers. • Selective photooxidation or reduction is achieved by inversion of catalyst geometry. • Metal ion deposition tests confirmed oxidation/reduction sites on different particle surfaces. • Lorentz force promoted charge separation enabled 98% SMZ degradation in 30 min. [ABSTRACT FROM AUTHOR]

Fabrication and optical testing of high-aspect-ratio 1D photonic crystals, obtained by electrochemical micromachining of silicon, are discussed in this paper. The devices consist of high-aspect-ratio periodic (P=4 mum) arrays of 1.22-mum-thick silicon walls separated by 2.78-mum-wide air gaps, with 100 mum etching depth. They were designed as hybrid quarter-wavelength reflectors with photonic bandgaps in the near-IR region, one in particular centered at lambda=1.55 mum. The fabrication process was improved to increase structure uniformity and strength. Thermal oxidation of the silicon structures was exploited to tune the wavelength position and width of the bandgaps. Fabricated devices, also with different silicon dioxide thicknesses, were optically tested by measuring their spectral reflectivity in the wavelength range of 1.0-1.7 mum. Experimental results were found in good agreement with the calculated spectra. [ABSTRACT FROM PUBLISHER]