Optical Absorption Characteristics Research Articles

Görünür-Işık ile Çalışan Fotokatalizör Hematitin Çinko ve Bakır ile Katkılanmasıyla Geliştirilmesinin Karşılaştırmalı İncelenmesi

The low cost, earth abundance, nontoxic, and efficient photocatalysts materials have a critical role in order to solve environmental issues. In this regard, hematite (α-Fe2O3) has received significant attention due to its desirable properties. In the present study, zinc-doped and copper-doped hematite nanoparticles were synthesized by the hydrothermal method. The photocatalytic features of produced nanopowders were investigated. The evaluations of photocatalytic activities of synthesized nanoparticles were executed by monitoring the degradation rate of Rhodamine B (RhB) under the solar simulator in heterogeneous photocatalysis. Compared to commercial Degussa TiO2 powder, the transition metal doped hematite (α-Fe2O3) samples showed better photocatalytic activities against RhB under the solar simulator. It was observed that even though there were no significant differences in their characteristic properties strongly affecting photocatalytic activity such as morphological features, optical absorption characteristics, and band gaps, Cu-doped α-Fe2O3 nanoparticles exhibited higher photocatalytic activity, which is %20 higher than the Zn-doped α-Fe2O3. The synthesized Cu-doped hematite nanoparticles are hopeful materials as a visible-light-driven photocatalytic material to degrade organic pollutants in aquatic media.

Ligand-induced charge transport modulation and enhanced photoresponse in hybrid MoS2/quantum dot phototransistors

Mix-dimensional heterostructures of colloidal quantum dots (QDs) and two-dimensional (2D) layered materials have attracted growing interest in photodetection due to the combination of high optical absorption and superior charge transport characteristic. However, the QD sensitizing layer usually introduces uncontrolled doping to the 2D materials originating from the capping ligands, which deteriorates the gate modulation capability and interfacial charge transfer efficiency. In this work, we demonstrated that the photoresponse of MoS2/QD hybrid phototransistor was greatly enhanced by selecting ligand treatment strategy. The carrier concentration and mobility in MoS2 could be effectively tuned via surface doping of 3-mercaptopropionic acid ligand, resulting in high on–off current ratio and low dark current of around 10 pA. The signal-to-noise ratio was improved by three orders of magnitude compared to the pristine MoS2 devices, indicating a dramatically enhanced photoresponse sensitivity. The specific detectivity reached 3.1 × 1013 Jones at the illumination power of 2.3 mW/cm2. The photoresponse speed of the hybrid device was enhanced by about 100 times, owing to the effective interfacial charge transfer which was revealed by the photoluminescence quenching and optoelectrical characterizations. Our work may push a new path to design the interface of mix-dimensional heterostructure and develop high-performance electronic and optoelectronic devices.

Seasonal Variability in Fine Particulate Matter Water Content and Estimated pH over a Coastal Region in the Northeast Arabian Sea

The acidity of atmospheric particles can promote specific chemical processes that result in the production of extra condensed phases from lesser volatile species (secondary fine particulate matter), change the optical and water absorption characteristics of particles, and enhance trace metal solubility that can function as essential nutrients in nutrient-limited environments. In this study, we present an estimated pH of fine particulate matter (FPM) through a thermodynamic model and assess its temporal variability over a coastal location in the northeast Arabian Sea. Here, we have used the chemical composition of FPM (PM2.5) collected during the period between 2017–2019. Chemical composition data showed large variability in water-soluble ionic concentrations (WSIC; range: 2.3–39.9 μg m−3) with higher and lower average values during the winter and summer months, respectively. SO42− ions were predominant among anions, while NH4+ was a major contributor among cations throughout the season. The estimated pH of FPM from the forward and reverse modes exhibits a moderate correlation for winter and summer samples. The estimated pH of FPM is largely regulated by SO42− content and strongly depends on the relative ambient humidity, particularly in the forward mode. Major sources of FPM assessed based on Positive matrix factorization (PMF) and air-mass back trajectory analyses demonstrate the dominance of natural sources (sea salt and dust) during summer months, anthropogenic sources in winter months and mixed sources during the post-monsoon season.

A Z-scheme BiYO3/g-C3N4 heterojunction photocatalyst for the degradation of organic pollutants under visible light irradiation.

Photocatalysis is one of the fascinating fields for the wastewater treatment. In this regard, the present study deals with an effective visible light active BiYO3/g-C3N4 heterojunction nanocomposite photocatalyst with various ratios of BiYO3 and g-C3N4 (1:3, 1:1 and 3:1), synthesised by a wet chemical approach. The as-synthesised nanocomposite photocatalysts were investigated via different physicochemical approaches like Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electrons microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and photoelectrochemical studies to characterise the crystal structure, morphology, optical absorption characteristics and photoelectrochemical properties. The photocatalytic degradation ability of the prepared photocatalytic samples was also analysed through the degradation of RhB in the presence of visible light irradiation. Of all the synthesised photocatalysts, the optimised CB-1 composite showed a significant photocatalytic efficiency (88.7%), with excellent stability and recyclability after three cycles. O2•- and •OH radicals were found to act a major role in the RhB degradation using optimised CB-1 composite, and it possessed ~ 1 times greater photocurrent intensity than the pristine g-C3N4 and BiYO3. In the present work, a direct Z-scheme heterojunction BiYO3/g-C3N4 with a considerably improved photocatalytic performance is reported.

2D Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene/MoS<sub>2</sub> heterostructure construction for nonlinear optical absorption modulation

Two-dimensional (2D) nonlinear optical mediums with high and tunable light modulation capability can significantly stimulate the development of ultrathin, compact, and integrated optoelectronics devices and photonic elements. 2D carbides and nitrides of transition metals (MXenes) are a new class of 2D materials with excellent intrinsic and strong light-matter interaction characteristics. However, the current understanding of their photo-physical properties and strategies for improving optical performance is insufficient. To address this issue, we rationally designed and <italic>in situ</italic> synthesized a 2D Nb₂C/MoS₂ heterostructure that outperforms pristine Nb₂C in both linear and nonlinear optical performance. Excellent agreement between experimental and theoretical results demonstrated that the Nb₂C/MoS₂ inherited the preponderance of Nb₂C and MoS₂ in absorption at different wavelengths, resulting in the broadband enhanced optical absorption characteristics. In addition to linear optical modulation, we also achieved stronger near infrared nonlinear optical modulation, with a nonlinear absorption coefficient of Nb₂C/MoS₂ being more than two times that of the pristine Nb₂C. These results were supported by the band alinement model which was determined by the X-ray photoelectron spectroscopy (XPS) experiment and first-principal theory calculation. The presented facile synthesis approach and robust light modulation strategy pave the way for broadband optoelectronic devices and optical modulators.

First principles study of electronic and optical properties of S-type heterostructures MoSi&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/GeC

In this article, the first principles calculation method is used to study the MoSi&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/GeC heterostructures, and calculate its structural, electronic, and optical properties. And the effects of different biaxial strains and vertical electric fields on the band structure and optical absorption characteristics of the heterostructures are also investigated. MoSi&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/GeC heterostructure is an indirect bandgap semiconductor with a bandgap of 1.25 eV, with the built-in electric field direction pointing from the GeC layer to the MoSi&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; layer. In addition, its photogenerated carrier transfer mechanism conforms to the S-type heterostructures mechanism, thus improving the oxidation reduction potential of photocatalytic water decomposition, making it fully meet the requirements of photocatalytic water decomposition with pH = 0–14. Under biaxial strain, the band gap first increases and then decreases with the increase of compressive strain, and the light absorption performance in the ultraviolet region increases with compressive strain increasing. The band gap decreases as tensile strain increases, and the light absorption performance in the visible light region is enhanced in comparison with its counterpart under compressive strain. Under a vertical electric field, the band gap increases with positive electric field increasing, and decreases with negative electric field increasing. In summary, MoSi&lt;sub&gt;2&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt;/GeC heterostructures can be used as an efficient photocatalytic material in some fields such as optoelectronic devices and photocatalysis.

A bimetallic Ag15Cu12(S-c-C6H11)18(CH3COO)3 nanocluster featuring an irregular Ag12 kernel.

Here, we report the synthesis and atomic structure of a Ag15Cu12(SR)18(CH3COO)3·(C6H14) nanocluster (Ag15Cu12 for short, SR denotes cyclohexanethiol), confirmed by single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). X-ray crystallographic analysis revealed that Ag15Cu12 consisted of an irregular Ag12 core, stabilized by the Ag3Cu12(SR)18(CH3COO)3 shell. The shell consisted of two nearly planar Cu3(SR)6 moieties, three monomeric [-SR-Ag-SR-] units and three Cu2(CH3COO) staples. Furthermore, time-dependent density functional theory (TD-DFT) simulation was performed to interpret the optical absorption features of Ag15Cu12. Overall, this work will broaden and deepen the understanding of Ag-Cu alloy nanoclusters.

Insight into the Effect of Anionic–Anionic Co-Doping on BaTiO3 for Visible Light Photocatalytic Water Splitting: A First-Principles Hybrid Computational Study

In this research, we thoroughly studied the electronic properties and optical absorption characteristics with double-hole coupling of anions–anion combinations for designing effective photocatalysts for water redox using first-principles methods within the hybrid Heyd–Scuseria–Ernzerhof (HSE06) exchange–correlation formalisms. The findings reveal that the values of formation energy of both the anion mono- and co-doped configurations increase monotonically as the chemical potential of oxygen decreases. The N–N co-doped BaTiO3 exhibits a more favorable formation energy under an O-poor condition compared with other configurations, indicating that N and N pairs are more likely to be synthesized successfully. Interestingly, all the co-doping configurations give a band gap reduction with suitable position for oxygen production and hydrogen evolution. The obtained results demonstrate that all the co-doped systems constitute a promising candidate for photocatalytic water-splitting reactions. Furthermore, the enhanced ability of the anionic-anionic co-doped BaTiO3 to absorb visible light and the positions of band edges that closely match the oxidation-reduction potentials of water suggest that these configurations are viable photocatalysts for visible-light water splitting. Therefore, the wide-band gap semiconductor band structures can be tuned by double-hole doping through anionic combinations, and high-efficiency catalysts for water splitting using solar energy can be created as a result.

Face-Centered Cubic Silver Nanoclusters Consolidated with Tetradentate Formamidinate Ligands.

Growing attention has been paid to nanoclusters with face-centered cubic (fcc) metal kernels, due to its structural similarity to bulk metals. We demonstrate that the use of tetradentate formamidinate ligands facilitate the construction of two fcc silver nanoclusters: [Ag52(5-F-dpf)16Cl4](SbF6)2 (Ag52, 5-F-Hdpf = N,N'-di(5-fluoro-2-pyridinyl)formamidine) and [Ag53(5-Me-dpf)18](NO3)5 (Ag53, 5-Me-Hdpf = N,N'-di(5-methyl-2-pyridinyl)formamidine). Single-crystal X-ray structural analysis revealed that the silver atoms in both clusters are in a layer-by-layer arrangement, which can be viewed as a portion of the fcc packing of silver. The nitrogen donors of amidinate ligands selectively passivate the {111} facets. All silver atoms are involved in the fcc packing, that is, no staple motifs are observed due to the linear arrangement of the four N donors of the dpf ligands. The characteristic optical absorption bands of Ag52 and Ag53 have been studied with a time-dependent density functional theory. This work provides a facile access to assembling atomically precise fcc-type nanoclusters and shows the prospect of amidinates as protecting ligands in synthesizing metal nanoclusters.

Optical bistability and absorption characteristic of an optomechanical system embedded with double quantum dot and nonlinear medium

This paper theoretically studies a hybrid optomechanical system embedded with two coupled quantum dots and a third-order Kerr nonlinear medium inside the cavity. The optical bistability and absorption spectrum are analyzed for the proposed system. From the Hamiltonian which describes the proposed system, a set of quantum Langevin equations are derived. Using these equations of motion, the steady-state mean field analysis is done which gives the phenomena of optical bistability. The performance of the optical switch is also analyzed in terms of gain and switching ratio. Further, the absorption spectrum of the system is derived and analyzed from the fluctuation dynamics. The optical bistability has the potential to design tunable all-optical switches. The absorption spectra display peculiar characteristics of negative absorption (transparency dip). The transparency dips are found to be strongly dependent on the frequency of the mechanical resonator. The results of our investigation reveal that the proposed system can be used as an optical switch and has numerous other applications in quantum communication systems.

All-fiber wavelength-tunable mode-locked cylindrical vector beams laser based on multimode interference

Cylindrical vector beams (CVBs) are of increasing concern due to their polarization and axially symmetrical distribution of field intensity. In this paper, we report for the first time an all-fiber single- and dual-wavelength tunable CVBs fiber laser using the nonlinear optical saturation absorption characteristics and filtering properties of nonlinear multimode interference (NL-MMI). In the experiment, the central wavelength of mode-locked CVBs fiber laser can be tuned from 1541 nm to 1564 nm at single-wavelength and from 1542.8 and 1562.925 nm to 1546.52 and 1563.86 nm at dual-wavelength. This NL-MMI-based wavelength-tunable ultrashort pulse CVBs fiber laser has excellent development prospects in optical communication.

Nonlinear optical absorption characteristics of PbMoO4 single crystal for optical limiter applications

Molybdate materials take great interest due to their photocatalytic and optoelectronic applications. In this report, PbMoO4 single crystal, one of the member of molybdate materials, is grown by Czochralski technique and the change of nonlinear absorption characteristic depending on the input intensity was reported. Linear absorption analysis revealed the band gap energy and Urbach energy as to be 3.12 and 0.52 eV, respectively. Nonlinear absorption characteristics of the PbMoO4 single crystal was examined with the open aperture (OA) Z-scan experiments at 532 nm excitation wavelength under various input intensities. Fitting results of the OA Z-scan experiments indicated that PbMoO4 single crystal has nonlinear absorption (NA) behavior, and NA coefficient (βeff) increased from 7.11 × 10−8 to 1.96 × 10−7 m/W with increasing input intensity. This observation was associated with the increase of the contribution of the free carrier absorption to the NA with the generation of more excited electrons with increasing input intensity. At the 532 nm excitation wavelength (2.32 eV), the dominant mechanisms were revealed as one photon and free carrier absorptions. The optical limiting threshold of the PbMoO4 single crystal was obtained to be 4.91 mJ/cm2. The reported results indicated that PbMoO4 single crystal can be a good optical limiter in the visible wavelength region due to its effective NA behavior.

Influence of tungsten trioxide (WO3) on the topographical, structural, optical absorption and electrochemical characteristics of BFO-MWCNT and BFO-Graphene nanocomposite ceramics

Nanocomposites of Bismuth Ferrite Oxide (BFO), Multi-Walled Carbon Nanotube (MWCNT)/ Graphene and Tungsten Oxide (WO3) have been prepared from sol-gel route for the first time. Synthesized composites of BFO-MWCNT-WO3 and BFO-Graphene-WO3 were subjected to XRD, optical absorption /reflectance and Raman scattering measurements. Field Emission Scanning Electron Microscopy (FESEM)images were recorded to understand the morphological features of the synthesized composites. Structural and spectral investigations ascertained the formation of the three component composite system. Tuning of band gap could be noticed from optical reflectance measurements. Cyclic Voltammetry (CV) measurements suggest the relatively better electrical characteristics of title composites over its individual moieties. The obtained results have been discussed in detail.

Improvement in optical absorption and emission characteristics of polymethyl methacrylate in solution cast polymethyl methacrylate/polyvinyl carbazole polyblends

Polymer blends have got considerable attention for their potential optoelectronic and photonic applications due to several advantages such as easy processing, low cost, flexibility, and good mechanical properties. This work reports the structure and optical properties of solution cast binary blends of poly (methyl methacrylate) (PMMA) and poly (vinyl carbazole) (PVK). Here, the position and/or intensity of characteristic FTIR peaks reveal the changes of the structure of PMMA on PVK content while the surface morphology changes from highly smooth for pure PMMA to flaky structured (PVK 5%) and then to agglomerated morphologies for these blends. A red shift in optical absorption edge and decrease in optical transmission with PVK content in PMMA based blends. The emission spectra exhibit intensity escalation by 340 times with respect to PMMA for PVK-15 blends and then decreases with further addition of PVK in these blends. These results are very important for the advent of new optoelectronic functionalities for these polymer blends.

Photo-electrochemical Effect in the Amorphous Cobalt Oxide Water Oxidation Catalyst Cobalt–Phosphate (CoPi)

The cobalt–phosphate amorphous oxyhydroxide water-splitting catalyst, CoPi, is widely investigated because of its reactivity and self-repair analogous to the oxygen-evolving catalyst in Photosystem II. CoPi films show optical absorption features analogous to those seen more generally in transition metal oxides and oxygen-evolving catalysts. Possible photocatalytic properties of CoPi have, up until now, not been considered. Herein, we report on the finding of wavelength-dependent photo-electrochemical responses in CoPi. Red light excitation (623 nm) into a manifold of charge transfer and d–d electronic transitions was seen to produce photoanodic current responses that enhance OER, while blue light excitation (415 nm) within the ligand-to-metal charge-transfer transition was found to produce photocathodic responses that inhibit OER and oxidative repair. These results demonstrate intrinsic wavelength-dependent photo-electrochemistry in CoPi and opportunities to use light-excited states in CoPi, and potentially other transition metal oxides, to enhance OER and to track reaction mechanisms using light-triggered, pump–probe techniques.

Weak Coordinating Character of Organosulfonates in Oriented Silica Films: An Efficient Approach for Immobilizing Cationic Metal-Transition Complexes.

Iron (II) tris(2,2′-bipyridine) complexes, [Fe(bpy)3]2+, have been synthesized and immobilized in organosulfonate-functionalized nanostructured silica thin films taking advantage of the stabilization of [Fe(H2O)6]2+ species by hydrogen bonds to the anionic sulfonate moieties grafted to the silica nanopores. In a first step, thiol-based silica films have been electrochemically generated on indium tin oxide (ITO) substrates by co-condensation of 3-mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS). Secondly, the thiol function has been modified to sulfonate by chemical oxidation using hydrogen peroxide in acidic medium as an oxidizing agent. The immobilization of [Fe(bpy)3]2+ complexes has been performed in situ in two consecutive steps: (i) impregnation of the sulfonate functionalized silica films in an aqueous solution of iron (II) sulfate heptahydrate; (ii) dipping of the iron-containing mesostructures in a solution of bipyridine ligands in acetonitrile. The in situ formation of the [Fe(bpy)3]2+ complex is evidenced by its characteristic optical absorption spectrum, and elemental composition analysis using X-ray photoelectron spectroscopy. The measured optical and electrochemical properties of immobilized [Fe(bpy)3]2+ complexes are not altered by confinement in the nanostructured silica thin film.

구리 나노입자/플레이크 잉크 및 레이저 공정을 이용한 고전도성 전극 제조

Printing techniques that enable the formation of arbitrarily designed architectures have been implemented in various research fields owing to their characteristic advantages in processing over other techniques. In particular, low-cost, printable conductors are of paramount importance in the production of highly functioning printed electronics. Among various candidates, copper (Cu) particle-based printable fluid has been regarded as the most promising constituent material in conjunction with the use of the laser sintering (LS) process in air. In this study, we incorporated surface-oxidation suppressed Cu nanoparticles and flakes to regulate the optical absorption characteristics in LS-processed, Cu-based printed conductors. Our results revealed that highly conductive, uniform Cu conductors can be generated with a conductivity of over 33,000 S/cm by printing and LS processes in air.

A novel approach to band gap engineering of Nano-Ca(OH)2: Nanocomposites with Ag2O

Band gap engineering (BGE) is an important tool to tune the energy band gap of wide band gap semiconductors e.g., Ca(OH)2 which promises to show many wonderful functional applications e.g., solar blind photodetectors. The current work reports about the successful reduction in optical energy band gap (Eg) through BGE of chemically synthesized Ca(OH)2 nano particles (CHNPs) by microstructural tuning achieved through in-situ Ag2O incorporation to achieve the formation of the Ca(OH)2–Ag2O nanocomposites. The CHNPs and (3–15 atom%) Ag2O-incorporated CHNPs nanocomposite powders are characterized by the conventional x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermo-gravimetric analysis-differential thermal analysis (TGA-DTA) and ultraviolet–visible (UV–Vis) UV–Vis spectroscopy techniques. The results reveal that systematic incorporation of nano Ag2O can very effectively reduce the magnitude of direct optical band gap energy values (Eg) by as much as 33%. These results are explained in terms of microstructural variables e.g., nanocrystallite size, lattice strain, lattice parameters, dislocation density, presence of Ag0, Ag+ states present on the surfaces of the nanocomposite powders, variation in microstructure, presence of surface functional groups, thermal stability, and optical absorption characteristics. The possible mechanisms active behind the reduction in the (Eg) values are suggested. Further, a schematic model of the band gap reduction mechanism is presented. Furthermore, the implications of the present results for designing CHNPs for futuristic applications e.g., optoelectronics are also presented.

Synthesis of core-shell polyhedron ZIF-8@ZIF-67 as saturable absorber for passive Q-switching operation in Tm:YAP laser at 3H4→3H5 transition

In this paper, we synthesized a novel core-shell polyhedron ZIF-8@ZIF-67 nanocomposites with a size of around 150 nm. Then the core-shell structure ZIF-8@ZIF-67 as a saturable absorber to passively Q-switch the Tm:YAP laser was demonstrated for the first time at 2.3 μm based on the Tm3+3H4 → 3H5 transition. ZIF-8@ZIF-67 possessed the excellent nonlinear optical absorption features with a large modulation depth of 6.7% at 2.3 μm. The obtained stable shortest pulse width was 208 ns with a repetition rate of 128 kHz. Moreover, to fully understand the nonlinear optical properties of the core-shell ZIF-8@ZIF-67 nanocomposites, the coupled rate equations were setup to simulate the 3H4→3H5 Q-switching operation. The numerical simulation results agreed well with the experimental results. It demonstrated that the ZIF-8@ZIF-67 core-shell nanocomposites feature great potential as saturable absorber candidate for the mid-infrared pulse generation.

Band structure alignment transitioning strategy for the fabrication of efficient photocatalysts for solar fuel generation and environmental remediation applications

Indium hydroxide (In(OH)3) and indium oxide (In2O3) have proven to be efficient catalysts for photocatalytic water-splitting reactions to produce hydrogen (H2) and for organic pollutant degradation applications. However, the limited optical absorption features of indium-based nanostructures have restricted their practical applications. In this study, we have successfully designed indium hydroxide- and indium oxide-loaded metal sulfide (cadmium sulfide, CdS) heterostructures as excellent photocatalytic systems for photocatalytic hydrogen evolution and tetracycline hydrochloride pollutant degradation reactions. In this system, In(OH)3 and In2O3 established Type-I and S-scheme heterojunctions, respectively, with CdS, resulting in superior charge separation properties and outstanding photocatalytic activity. Specifically, the rational and appropriate design of the aforementioned indium-based heterostructures promoted the separation of photoexcited charge carriers via Type-I and S-scheme paths. Accordingly, enhanced photocatalytic H2 evolution activities of 9.58 and 14.98 mmol·g−1·h−1 were achieved for CdS–In(OH)3 and CdS–In2O3, respectively. Furthermore, the highest degradation efficiency of CdS–In2O3 was ∼ 90%, which was higher than those of CdS–In(OH)3 (72%) and bare CdS nanorods (51%). Therefore, the results of this study provide an opportunity to enhance the catalytic activities of heterostructured photocatalytic systems by utilizing the strategy of transitioning band structure alignment from the Type-I to the S-scheme.