Enhancement Of Absorption Coefficient Research Articles

An insight in to microwave induced defects and its impact on nonlinear process in NiO nanostructures under femtosecond and continuous wave laser excitation.

This work demonstrates the impact of microwave (MW) irradiation on third-order nonlinear optical (NLO) processes in chemically deposited NiO nanostructure films. The optical nonlinearity of the NiO nanostructure films was studied using third-harmonic generation (THG) measurements in the pulsed femtosecond laser regime and the Z-scan technique in the continuous wave laser regime. In the ultrafast pulsed regime, THG measurements revealed a significant increase in the THG signal of MW-irradiated NiO nanostructures due to photoexcitation and relaxation processes, resulting from an enhancement in defect concentration. This increase in defect density upon MW irradiation was quantified by PL and XPS studies. Under continuous wave laser irradiation, the Z-scan technique showed an enhanced absorption coefficient of ∼10-1 m W-1 and a nonlinear refractive index of ∼10-7 m2 W-1. The high NLO values in both pulsed and continuous laser regimes indicate that MW-irradiated NiO nanostructure films hold promise for optoelectronic device applications.

Electric-magnetic dual-gradient structure design of thin MXene/Fe3O4 films for absorption-dominated electromagnetic interference shielding

The challenge of achieving high-performance electromagnetic interference (EMI) shielding films, which focuses on electromagnetic waves absorption while maintaining thin thickness, is a crucial endeavor in contemporary electronic device advancement. In this study, we have successfully engineered hybrid films based on MXene nanosheets and Fe3O4 nanoparticles, featuring intricate electric–magnetic dual-gradient structures. Through the collaborative influence of a unique dual-gradient structure equipped with transition and reflection layers, these hybrid films demonstrate favorable impedance matching, abundant loss mechanisms (Ohmic loss, interfacial polarization and magnetic loss), and an “absorb-reflect-reabsorb” process to achieve absorption-dominated EMI shielding capability. Compared with the single conductive gradient structure, the dual-gradient structure effectively enhances the absorption intensity per unit thickness, and thus reduces the thickness of the film. The optimized film demonstrates a remarkable EMI shielding effectiveness (SE) of 49.98 dB alongside an enhanced absorption coefficient (A) of 0.51 with a thickness of only 180 μm. The thin films with a dual-gradient structure hold promise for crafting absorption-dominated electromagnetic shielding materials, highlighting the potential for advanced electromagnetic protection solutions.

First-principles studies of the stability, structural, electronic, magnetic and optical properties of halogen atom doped marcasite FeS2

The effects of halogen atom (F, Cl, Br or I) doping on the stability, structural, electronic, magnetic and optical properties of marcasite FeS2 (m-FeS2) are investigated through the first-principles calculations. The formation energies are relatively small under Fe-rich condition, indicating that it is feasible to implant halogen atom into m-FeS2. The ground state of halogen atom doped m-FeS2 systems is magnetic due to the positive energy differences between non-spin-polarized and spin-polarized states. Phonon dispersion curves show that all doping systems are dynamically stable. The total magnetic moment of all doping systems is nearly 1μB, since replacing the S atom with a halogen atom introduces a non-bonding electron. Most of them come from Fe and S atoms, and only a small fraction come from the dopant. The simulation results show that F- and Br-doped m-FeS2 systems are still semiconductors although the band gaps are reduced considerably, Cl-doped m-FeS2 changes to a half-metal with half metallic band gap of 0.25 eV, while I-doped m-FeS2 becomes a metal, making them potentially useful in spintronics. In addition, the halogen atom doped m-FeS2 systems possess enhanced absorption coefficient and red-shifted absorption edge. So they are promising in optoelectronic device and solar energy harvesting.

Energy gap measurements based on enhanced absorption coefficient calculation from transmittance and reflectance raw data

The absorption coefficient plays an important role in studying and characterizing semiconducting materials. It is an important parameter to study the mechanism of photons absorption within the structure of the studied material. Thus, it helps to study the several types of charge carrier transport along with the energy band structure and its defects. In literature, a formula was reported to precisely calculate the absorption coefficient from raw data of transmittance and reflectance of electromagnetic radiation. However, the reported formula has several issues limiting its validity in the literature. In this paper, we provide a more mathematically accurate form of this equation to precisely obtain the absorption coefficient from the raw data, by considering the total internal reflection at the different interfaces. Moreover, the equation is tested by simulated data and is applied to study the optical characteristics of a single-component epoxy resin from its transmittance and reflectance raw data.

Growth of Cr,Yb:YAG single crystals for self-Q-switched monolithic solid-state lasers

The saturable absorbers play key role in passively Q-switched lasers, and Cr4+-doped crystals present attractive advantages for Yb:YAG lasers. At present the major problem is the low doping concentration of Cr4+ and the effective way to promote Cr3+→Cr4+ conversion. From this view, we introduce divalent additives Ca2+ and Mg2+ as charge compensators to ensure the charge state of Cr4+ in the tervalence environment of Yb:YAG. The results reveal that this method can promote Cr3+→Cr4+ conversion effectively and an optimal CaO/MgO ratio is 1:4. The corresponding Cr0.01at.%,Yb5at.%:YAG single crystals present enhanced absorption coefficients and fluorescence intensity at 941 nm and 1030 nm, and decreased fluorescence lifetimes and decay curves than Yb:YAG. The thermal expansion coefficient and laser damage threshold of Cr,Yb:YAG single crystal are approaching the YAG host material. The results show that Cr,Yb:YAG crystal has good potential for self-Q-switched monolithic solid-state lasers.

Furan Donor for NIR-II Molecular Fluorophores with Enhanced Bioimaging Performance.

The second near-infrared (NIR-II, 1,000 to 1,700 nm) molecular fluorophores containing donor-acceptor-donor conjugated backbone have attracted substantial attention due to their outstanding advantages, such as stable emission and facilely tuned photophysical properties. However, it is still challenging for them to simultaneously achieve high brightness and red-shifted absorption and emission. Herein, furan is adopted as the D unit to construct NIR-II fluorophores, demonstrating red shift of absorption, enhanced absorption coefficient, and fluorescent quantum yield when compared with the generally used thiophene counterparts. The high brightness and desirable pharmacokinetics of the optimized fluorophore, IR-FFCHP, endows improved performance for angiography and tumor-targeting imaging. Furthermore, dual-NIR-II imaging of tumor and sentinel lymph nodes (LNs) has been achieved with IR-FFCHP and PbS/CdS quantum dots, enabling the in vivo imaging navigated LN surgery in tumor-bearing mice. This work demonstrates the potential of furan for constructing bright NIR-II fluorophores for biological imaging.

The upsurge of absorption coefficient in CuInS2 thin film with Ru doping: an energetic absorber layer in a superstrate solar cell

In this work, a clear increase in electrical mobility and absorption coefficient has been demonstrated in spray pyrolysis-deposited CuInS2 (CIS) thin films by ruthenium (Ru) doping. This film was then employed as an efficient absorber layer in superstrate photovoltaic cells for the first time. Ru doping into the CIS tetragonal crystal structure increases the tensile strain causing structural modifications including average crystallite size and dislocation density. Further, the Ru causes an adjustment in the Brillouin zone boundary of the CIS semiconductor leading to alternative morphologies on the surface of the substrate such as particles (2 wt%), rods (4 wt%), and leaf-like mixed nanoparticles (6 wt%). The absorbance and emission properties of this CIS absorber layer were studied for possible enhancement in optical properties due to the surface modification. A higher absorption coefficient (1.20 × 106 cm−1 compared to pristine CIS 0.84 × 106 cm−1) was observed in the Ru-doped CIS film. The possibility for Ru-4d to S-3p transition explains the electronic origin of an enhanced absorption coefficient in Ru-doped CIS thin films. The atomic elements such as Cu, In, S, and Ru and their corresponding 1+, 3+, 2−, and 4+ oxidation states remained unchanged following doping illustrating an intact lattice. The Ru-doped CIS films, optimized at 6 wt%, exhibited both higher electrical and photo responses as compared to a pristine CIS film. Solar cells were fabricated using the ITO/AZO/CdS/CuInS2 superstrate configuration with and without the Ru doping (0 and 6 wt% Ru-doped CIS)/Au showing an increase from 2.84% to 4.46% PCE a 1.62% increase overall. Following this, similar durability over 500 h was observed in both device types.

Influence of twisted or planar linkers on the performance of quasi-two-dimensional fused perylene diimide acceptors for organic solar cells

Quasi-two-dimensional (quasi-2D) fused perylene diimide building block is effective for constructing high-performance non-fullerene acceptors, while the exploration of their structure-property relationship remains critical, yet challenging. Herein, two quasi-2D non-fullerene acceptors (FPDI-V and FPDI-E) featuring vinylene or ethynylene linker were developed to reveal the effects of molecular geometry on photophysics, morphology and device performances. We observed that such minor chemical variations can lead to distinct difference on absorption spectra, energy levels, and the photovoltaic properties, but only have slight effects on crystallinity, molecular packing and film morphology. The resulting device based on PTB7-Th:FPDI-V delivered a power conversion efficiency of 7.53%, which is higher than those of FPDI-E based device (6.37%). The improved photovoltaic performance of FPDI-V with a twisted vinylene linker should come from the enhanced absorption coefficient, upshifted molecular energy levels, higher exciton dissociation rate, and weaker charge recombination. This result provides an updated idea for further designing and structural optimizing of quasi-2D non-fullerene acceptors.

Modulation of the optoelectronic properties of CdSe2

Based on density functional theory, the first-principles calculations are carried out to study the optoelectronic properties of CdSe2 under hydrostatic pressure. The GGA calculation predicts the energy band gap of 0.546 eV that has been enhanced to 1.473 eV due to the inclusion of mBJ functional in the study. The current theoretical calculations present semiconductor to metal transitions at 5.1 GPa for GGA and 8.1 GPa for mBJ functional. The application of pressure (10 GPa and −8 GPa) has also successfully reproduced better optical responses like refractive index, reflectivity, and optical conductivity with an enhanced absorption coefficient of 4.867 × 105 cm−1. Their optical and electronic properties are of particular interest and suitable for applications in optoelectronics as photovoltaic devices, light emitters, and detectors.

Water-soluble near-infrared fluorescent heptamethine dye for lymphatic mapping applications

The identification of sentinel lymph node (SLN) is an important method for prognostic evaluation and minimally invasive staging of metastatic tumors. Here, we report a series of near-infrared fluorescent heptamethylamine dyes (series A, B and C) with central cycloalkene ring modified by tyrosine or N-Boc tyrosine via ether linkage. N-Boc tyrosine/tyrosine modification provided enhanced absorption coefficient and fluorescence quantum yield in DMSO, however with slight hypsochromic shift compared to the mother dyes in DMSO. In PBS, series A and B were found to be more fluorescent than ICG and showed brighter images. Compound A1 was found to exhibit the most favorable imaging performance among all the dyes investigated and was selected for in vivo sentinel lymph node mapping experiments in mice. A1 showed faster response and stronger fluorescence emission than FDA-approved ICG. The lymph node tracing with A1 could be assisted by MB staining. Ex vivo imaging of harvested organs indicated that similar metabolic characteristics of A1 and ICG. Overall, A1 is advantageous over ICG and is very promising for non-invasive lymph node imaging.

First-principles prediction of stable Janus BiSbC3 monolayer with tunable electronic and optical properties under strain

In this study, first-principles calculations were used to study the structural, electronic and optical properties of a novel stable Janus BiSbC3 monolayer under varied biaxial strain levels. The structural and phonon dispersion calculations show that the novel Janus BiSbC3 is thermodynamically stable. At the equilibrium state, our results show that the Janus BiSbC3 monolayer is a direct semiconductor with a suitable energy band gap of 0.86 eV, which is converted to an indirect band gap with a biaxial tensile strain of +4%. It is worth noting that compressions strain of −8% causes a semiconductor-metal phase transition. The optical properties such as dielectric constant, reflectivity, extinction coefficient and absorption coefficient improved under biaxial strain with an enhanced absorption coefficient in the infrared and visible regions. Interestingly, a high absorption coefficient of 15.30×106cm−1 in the visible region under biaxial strain was predicted. Our calculations show that the novel Janus BiSbC3 monolayer has potential applications in optoelectronics and optical devices.

Tunable properties of the stable SiSeS Janus monolayer under biaxial strain: First-principles prediction

The electronic structure, optical and thermoelectric properties of Janus T-phase SiSeS monolayer under biaxial strain have been analyzed using the first-principles calculations. Our calculations identified the Janus T-phase SiSeS monolayer as an indirect semiconductor with an energy band gap of 0.77 eV at the equilibrium state, which can be tuned effectively through a biaxial strain. The band gap tends to decrease slowly when the large compression biaxial strains are applied. It is of interest that a semiconductor-metal phase transition was obtained under biaxial compression strain of − 8%. Moreover, the optical properties rise under biaxial strain with an enhanced absorption coefficient in the infrared region. Interestingly, the compressive biaxial strain combined with p-type doping in the Janus T-phase SiSeS monolayer produced a large electronic figure of merit (ZTe) of 7.0 at 300 K. The predicted results show the potential applications of Janus T-phase SiSeS monolayer for optoelectronic and thermoelectric devices.

All-Polymer Solar Cells Incorporating Readily Accessible Naphthalene Diimide and Isoindigo Acceptor Polymers for Improved Light Harvesting

The development of readily accessible polymer acceptors is imperative to preserve the guiding principles of all-polymer solar cells as a low-cost and sustainable technology for alternative energy production. In this study, we report a computationally guided design and facile synthesis of new acceptor polymers comprising the alternating copolymer, PNIT, and the corresponding random copolymer, r-PNIT, which incorporate structurally simple naphthalene diimide (NDI) and isoindigo (IID) units. PNIT was prepared via direct arylation polymerization (DArP), which proceeds via C–H activation and avoids the use of toxic reagents and extended synthetic pathways for the monomer synthesis. PNIT has broad optical absorption in the 300–850 nm range and an enhanced absorption coefficient (47 × 103 cm–1) compared to r-PNIT (300–850 nm; 40 × 103 cm–1). When incorporated in all-polymer solar cells (APSCs) using PBDB-T as the donor polymer, PBDB-T:PNIT provides greater than two times the average (maximum) power conversion efficiency (PCE) of 5.18 ± 0.08 (5.32)% compared to that of PBDB-T:r-PNIT, 2.38 ± 0.16 (2.57)%, due to increased Jsc (10.36 vs 5.45 mA cm–2) and fill factor (FF) (0.58 vs 0.50) metrics. The PBDB-T:PNIT PCE is among the highest reported for an IID-based APSC and demonstrates the viability of DArP for the synthesis of new APSC acceptor polymers. Detailed morphological and microstructural investigations using atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS), respectively, reveal enhanced texturing for PNIT, which enhances charge transport properties as supported by space-charge-limited current (SCLC) mobility measurements.

On the role of Zn doping on tuning the electronic and optical properties of MnCr2O4 spinel via Mn0.5Zn0.5Cr2O4 doping scheme: A first-principles quantum computational analysis

Herein, we report on the impact of Zn doping on electronic and optical properties of manganese di-chromium oxide spinel MnCr2O4 via Mn0.5Zn0.5Cr2O4 doping scheme. For the quantum computational analysis on the targeted properties, we employed first-principles density functional theory approach within full-potential linearized augmented plane wave method by Modified Becke–Johnson potential. The calculated partial and total density of states revealed a strong hybridization among electronic orbitals of the constituent species while the asymmetric spin-polarized profiles of density of states showed magnetic nature of the spinels. The major interspecies spin interaction in the degenerate valence band is via (Mn + Cr + O ) from −7 eV to Fermi level for spin up polarization. Interestingly, we predict a reduction in band gap of MnCr2O4 to order 1eV subjected to the Zn doping, which considerably modified the electronic and optical properties of the doped spinels Mn0.5Zn0.5Cr2O4 in contrast to its undoped counterpart. In particular, we predict an enhancement in absorption coefficient, energy loss function, reflectivity, dielectric constant and refractive index for Mn0.5Zn0.5Cr2O4 spinels at some regions of ultraviolet energy spectrum. The calculated static refractive index of MnCr2O4 is 1.59 and for Mn0.5Zn0.5Cr2O4 it is 1.4. The optoelectronic properties indicate the promising prospects of the Zn-doped spinels for potential application in optoelectronic devices.

First-principles investigations on the feasibility of the GQD-PEB/PUB nanocomposites as the sensitizer of DSSC

The feasibility of nanocomposites of phycourobilin (PUB) and phycoerythrobilin (PEB) with graphene quantum dot (GQD) as a dye-sensitized solar cell (DSSC) sensitizer is studied based on the first-principles density functional theory including solvent effect. We construct and optimize the geometrical configurations for the nanocomposites of GQD-PEB/PUB and confirm the stability by the vibrational frequency and formation energy. The results of electronic properties show that the GQD2-PEB nanocomposite could be a favorable candidate for the sensitizer of DSSC due to its apparent spatial charge separation, suitable energies of frontier orbital, and enhanced absorption coefficient in the large solar irradiance region.

Strain engineered electronic structures and optical response of InS single crystal with negative Poisson's ratio

In this study, we propose a novel strain engineering strategy to tune the electronic structures and optical properties of InS single crystal. InS single crystal has the negative Poisson's ratio character in the zigzag and armchair directions, and owns a direct band-gap of 3.027 eV at the static state. There is a transition from direct to indirect band gap for different deformation modes (uniaxial strains εx, εy, εz, and biaxial strain εy≡εz). For the compressive strain mode, the band gap of InS single crystal first increases and then decreases with the increasing strain, and it changes from a direct to an indirect band gap at a critical strain. However, for the tensile strain pattern, the band gap of InS single crystal monotonously decreases with the increasing strain. It also changes from a direct to an indirect band gap at a critical strain. The biaxial strain mode εy≡εz among all the stretching modes is the most advantageous way to realize the strain-dependent band gap engineering of InS single crystal. Thus, for all the considered strain modes, with the increasing strain, InS single crystal exhibits the enhanced absorption coefficient accompanied by the red-shifted optical absorption edge.

Enhanced absorption in the space charge region of GaAs solar cells

The photo-generated currents of GaAs solar cells with different lengths of space charge region are obtained and analyzed in this study. The enhanced absorption coefficient in the space charge region is adopted to calculate the photo-generated current based on the solar cell physics theory. The calculated currents coincide well with the experimental currents both under single wavelength incidence and solar spectrum irradiation conditions.

A wide-bandgap π-conjugated polymer for high-performance ternary organic solar cells with an efficiency of 17.40%

Although substantial progress has been made at increasing power conversion efficiencies (PCEs) the field of ternary organic solar cells (TOSCs) during the past few years, choice of π-conjugated polymers that exhibit strong complementary spectra and achieve high photovoltaic parameters (open-circuit voltage ( V oc), short-circuit current density ( J sc), fill factor (FF), and PCE) simultaneously is limited. In this paper, TOSCs demonstrated a high PCE of 17.09% based on a π-conjugated polymer (named SiCl-BDT, bandgap ≈ 1.84 eV) as a third component (15 wt%) to the host binary system consisting of a PM7:Y7. The third component was used to achieve enhanced absorption coefficient (λ max = 5.5 × 10 4 cm −1 ) and more balanced charge carrier transport, frontier molecular orbital (FMO) energy levels, and blend miscibility, contributed to an improved FF of 70.38% and yielded an impressive J sc of 27.37 mA/cm 2 and V oc of 0.84 V. The PCE was higher than the host PM7:Y7 (15.13%) binary device. In addition, we found the photovoltaic performance of TOSCs could be further increased to a benchmark PCE of 17.40% using an interface engineering strategy. Thus, enables efficient charge transfer in TOSCs compared with that of without interlayer TOSCs, leading to high J sc, V oc. The resulting encapsulation-free TOSCs showed excellent ambient and thermal stability. Accordingly, this work suggests that the use of a passivated electron transporting layer (ETL) and a π-conjugated polymer as a third component offers a promising means of overcoming the lower PCEs of OSCs. • The devices were fabricated in binary and ternary organic solar cells (TOSCs). • The cascade LUMO alignment and complementary absorption improve the performance of TOSCs. • The PCE of SiCl-BDT incorporated with binary host device (PM7:Y7) TOSCs reached to 15.12%, 17.09%. • An improved efficiency of 17.40% was achieved in a TOSC device using 3-(1-pyridinio)-1-propanesulfonate as a ZnO-passivation layer. • PM7:SiCl-BDT:Y7 based devices exhibit good thermal and ambient stability.

NIR-II Fluorescent Brightness Promoted by "Ring Fusion" for the Detection of Intestinal Inflammation.

Fluorophores with emission in the second near-infrared window (NIR-II) have displayed salient advantages for biomedical applications. However, the common strategy of reducing the energy bandgap of fluorophores so as to achieve red-shifted wavelengths always leads to compromised fluorescent brightness. Herein, we propose a molecular design concept of "ring-fusion" to modify the acceptor of AIEgen that can extend the luminous wavelength from NIR-I to NIR-II. The fused-acceptor-containing fluorophore yielded, TTQP, has an enhanced absorption coefficient with a higher brightness in nanoparticle formation compared to its NIR-I emissive counterpart (TTQ-DP) with a non-fused acceptor. Theoretical calculation further confirms that the ring fusion can efficiently promote the rigidity and planarity of the electron-deficient core, leading to a lower reorganization energy and nonradiative decay. The TTQP NPs yielded thus allow sensitive NIR-II fluorescence imaging of vasculature and intestinal inflammation in mice models. Therefore, we anticipate that our work will provide a promising molecular-engineering strategy to enrich the library and broaden the application scope of NIR-II fluorophores.

A camouflage coating with similar solar spectrum reflectance to leaves based on polymeric inorganic composite

To realize the hyperspectral camouflage under the background of vegetation, a camouflage polyvinyl alcohol coating containing lithium chloride and green pigment particles of chromium sesquioxide (Cr2O3) was prepared on a stainless-steel substrate. Based on the four flux Kubelka-Munk model, the reflectances of the coatings with different volume fractions of Cr2O3 (f c) were predicted and compared with those of the membranes without substrate. The results show that when f c reaches 0.8%, the 0.2 mm thick coating can conceal the reflectance characteristics of the stainless-steel substrate. The reflectances of the coatings with the volume fraction of water (f w) in the range from 0% to 50% were also calculated via the model. It is found that the reflectances around 1460 nm and 1940 nm decrease with increased f w due to the significantly enhanced absorption coefficient, and the correlation coefficient between the spectral reflectances of the camouflage coating and an Osmanthus fragrans leaf increases from 0.913 to 0.954, indicating that the coating camouflage performance can be improved by increasing f w.