Showing papers on "Absorption spectroscopy published in 2021"

A Well-Mixed Phase Formed by Two Compatible Non-Fullerene Acceptors Enables Ternary Organic Solar Cells with Efficiency over 18.6%

Abstract: The ternary strategy, introducing a third component into a binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The judicious selection of an appropriate third component, without sacrificing the photocurrent and voltage output of the OSC, is of significant importance in ternary devices. Herein, highly efficient OSCs fabricated using a ternary approach are demonstrated, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. The three components show complementary absorption spectra and cascade energy alignment. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both the donor and acceptor materials, and optimizes the ternary blend morphology. Moreover, the addition of L8-BO-F into the binary blend suppresses the non-radiative recombination, thus leading to a reduced voltage loss. Consequently, concurrent increases in open-circuit voltage, short-circuit current, and fill factor are realized, resulting in an unprecedented PCE of 18.66% (certified value of 18.2%), which represents the highest efficiency values reported for both single-junction and tandem OSCs so far.

Gram-scale synthesis of carbon quantum dots with a large Stokes shift for the fabrication of eco-friendly and high-efficiency luminescent solar concentrators

Abstract: Luminescent solar concentrators (LSCs) are large-area sunlight collectors coupled to small area solar cells, for efficient solar-to-electricity conversion. The three key points for the successful market penetration of LSCs are: (i) removal of light losses due to reabsorption during light collection; (ii) high light-to-electrical power conversion efficiency of the final device; (iii) long-term stability of the LSC structure related to the stability of both the matrix and the luminophores. Among various types of fluorophores, carbon quantum dots (C-dots) offer a wide absorption spectrum, high quantum yield, non-toxicity, environmental friendliness, low-cost, and eco-friendly synthetic methods. However, they are characterized by a relatively small Stokes shift, compared to inorganic quantum dots, which limits the highest external optical efficiency that can be obtained for a large-area single-layer LSC (>100 cm2) based on C-dots below 2%. Herein, we report highly efficient large-area LSCs (100–225 cm2) based on colloidal C-dots synthesized via a space-confined vacuum-heating approach. This one batch reaction could produce Gram-scale C-dots with a high quantum yield (QY) (∼65%) using eco-friendly citric acid and urea as precursors. Thanks to their very narrow size distribution, the C-dots produced via the space-confined vacuum-heating approach had a large Stokes shift of 0.53 eV, 50% larger than C-dots synthesized via a standard solvothermal reaction using the same precursors with a similar absorption range. The large-area LSC (15 × 15 × 0.5 cm3) prepared by using polyvinyl pyrrolidone (PVP) polymer as a matrix exhibited an external optical efficiency of 2.2% (under natural sun irradiation, 60 mW cm−2, uncharacterized spectrum). After coupling to silicon solar cells, the LSC exhibited a power conversion efficiency (PCE) of 1.13% under natural sunlight illumination (20 mW cm−2, uncharacterized spectrum). These unprecedented results were obtained by completely suppressing the reabsorption losses during light collection, as proved by optical spectroscopy. These findings demonstrate the possibility of obtaining eco-friendly, high-efficiency, large-area LSCs through scalable production techniques, paving the way to the lab-to-fab transition of this kind of devices.

Femtosecond time-resolved spectroscopic observation of long-lived charge separation in bimetallic sulfide/g-C3N4 for boosting photocatalytic H2 evolution

Abstract: Copper-nickel sulfides could effectively suppress deep trapping states of active charge in carbon nitride. It also improves the efficiency of the shallow trapped electron transfer through C S bond for enhancing visible-light-driven photocatalytic hydrogen production with rates up to 752.8 μmol h−1 g−1, that is 470 times higher than that of pristine g-C3N4 (1.6 μmol h−1 g−1) so far. The kinetic coupling of electron transfer and long-lived charge separation (∼ 4896 ps) are systematically investigated by femtosecond time-resolved absorption spectroscopy (fs-TA). The TA signal of the composite is quenched by hole sacrificial agent, assigning to the effective hole extraction for high photocatalytic activity. Furthermore, a remarkable near-infrared-driven photocatalytic H2 evolution (0.32 μmol h−1 g−1, λ > 800 nm) was achieved due to the hole transfer from copper-nickel sulfide to the trap state of g-C3N4, indicating that the strong interaction between copper-nickel sulfide and g-C3N4 is favorable to charge transfer and long-lived charge separation states.

Low-Valence Znδ+ (0<δ<2) Single-Atom Material as Highly Efficient Electrocatalyst for CO2 Reduction

Abstract: A nitrogen-stabilized single-atom catalyst containing low-valence zinc atoms (Znδ+ -NC) is reported. It contains saturated four-coordinate (Zn-N4 ) and unsaturated three-coordinate (Zn-N3 ) sites. The latter makes Zn a low-valence state, as deduced from X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory. Znδ+ -NC catalyzes electrochemical reduction of CO2 to CO with near-unity selectivity in water at an overpotential as low as 310 mV. A current density up to 1 A cm-2 can be achieved together with high CO selectivity of >95 % using Znδ+ -NC in a flow cell. Calculations suggest that the unsaturated Zn-N3 could dramatically reduce the energy barrier by stabilizing the COOH* intermediate owing to the electron-rich environment of Zn. This work sheds light on the relationship among coordination number, valence state, and catalytic performance and achieves high current densities relevant for industrial applications.

Probing the enhanced methanol electrooxidation mechanism on platinum-metal oxide catalyst

Abstract: Pt-metal oxide nanocomposites are classified as an alternative promising catalyst besides Pt-Ru nanoalloys for electrochemical methanol oxidation reaction (MOR), and yet the relevant enhancement mechanism for MOR remains largely elusive in terms of catalyst functions and reaction pathways. Herein, interface-rich Pt-SnO2 nanoflakes supported on reduced graphene oxide have been prepared and employed as a model catalyst for such a study. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy measurements reveal significant electronic structure modification on Pt in contact with SnO2, concomitant with enhanced MOR. In-situ surface enhanced infrared absorption spectroscopy and on-line differential electrochemical mass spectrometry measurements indicate that the non-CO pathway is selectively enhanced on Pt-SnO2 compared to the CO pathway which prevails on Pt. DFT calculations reinforce that this electronic structure manipulation favors the non-CO reaction pathway on Pt-SnO2.

Monodisperse Long-Chain Sulfobetaine-Capped CsPbBr3 Nanocrystals and Their Superfluorescent Assemblies

Abstract: Ligand-capped nanocrystals (NCs) of lead halide perovskites, foremost fully inorganic CsPbX3 NCs, are the latest generation of colloidal semiconductor quantum dots. They offer a set of compelling characteristics-large absorption cross section, as well as narrow, fast, and efficient photoluminescence with long exciton coherence times-rendering them attractive for applications in light-emitting devices and quantum optics. Monodisperse and shape-uniform, broadly size-tunable, scalable, and robust NC samples are paramount for unveiling their basic photophysics, as well as for putting them into use. Thus far, no synthesis method fulfilling all these requirements has been reported. For instance, long-chain zwitterionic ligands impart the most durable surface coating, but at the expense of reduced size uniformity of the as-synthesized colloid. In this work, we demonstrate that size-selective precipitation of CsPbBr3 NCs coated with a long-chain sulfobetaine ligand, namely, 3-(N,N-dimethyloctadecylammonio)-propanesulfonate, yields monodisperse and sizable fractions (>100 mg inorganic mass) with the mean NC size adjustable in the range between 3.5 and 16 nm and emission peak wavelength between 479 and 518 nm. We find that all NCs exhibit an oblate cuboidal shape with the aspect ratio of 1.2 × 1.2 × 1. We present a theoretical model (effective mass/k·p) that accounts for the anisotropic NC shape and describes the size dependence of the first and second excitonic transition in absorption spectra and explains room-temperature exciton lifetimes. We also show that uniform zwitterion-capped NCs readily form long-range ordered superlattices upon solvent evaporation. In comparison to more conventional ligand systems (oleic acid and oleylamine), supercrystals of zwitterion-capped NCs exhibit larger domain sizes and lower mosaicity. Both kinds of supercrystals exhibit superfluorescence at cryogenic temperatures-accelerated collective emission arising from the coherent coupling of the emitting dipoles.

Deciphering the Oxygen Absorption Pre‐edge: A Caveat on its Application for Probing Oxygen Redox Reactions in Batteries

Abstract: The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr3+/6+. This work provides a critical clarification on O-K pre-edge interpretation and more importantly, a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.

Photoluminescence Spectroscopy Measurements for Effective Condition Assessment of Transformer Insulating Oil

Abstract: Condition assessment of insulating oil is crucial for the reliable long-term operation of power equipment, especially power transformers. Under thermal aging, critical degradation in oil properties, including chemical, physical, and dielectric properties, occurs due to the generation of aging byproducts. Ultraviolet-visible (UV-Vis) spectroscopy was recently proposed for the condition assessment of mineral oil. However, this absorption technique may involve all electronic states of the investigated material which typically yield a broad spectrum, and thus cannot precisely reflect the electronic structure of aged oil samples. It also cannot be implemented as an online sensor of oil degradation. In this paper, photoluminescence (PL) spectroscopy is introduced, for the first time, for effective condition assessment of insulating oil. The PL technique involves emission processes that only occur between a narrow band of electronic states that are occupied by thermalized electrons and consequently yields a spectrum that is much narrower than that of the absorption spectrum. Aged oil samples with different aging extents were prepared in the laboratory using accelerated aging tests at 120 °C, under which 1 day of laboratory aging is equivalent to approximately 1 year of aging in the field. These aged samples were then tested using PL spectroscopy with a wavelength ranging from 150 nm to 1500 nm. Two main parameters were evaluated for quantitative analysis of PL spectra: The full width at half-maximum and the enclosed area under the PL spectra. These parameters were correlated to the aging extent. In conjunction with PL spectroscopy, the aged oil samples were tested for the dielectric dissipation factor as an indication of the number of aging byproducts. Interestingly, we find a correlation between the PL spectra and the dielectric dissipation factor. The results of PL spectroscopy were compared to those of UV-Vis spectroscopy for the same samples and the parameters extracted from PL spectra were compared to the aging b-products extracted from UV-Vis spectra. Finally, the corresponding physical mechanisms were discussed considering the obtained results and the spectral shift for each spectrum. It was proved that PL spectroscopy is a promising technique for the condition assessment of insulating oil when compared to conventional transformer oil assessment measuring techniques and even to other optical absorption techniques.

Hybridization of Molecular and Graphene Materials for CO2 Photocatalytic Reduction with Selectivity Control.

Abstract: In the quest for designing efficient and stable photocatalytic materials for CO2 reduction, hybridizing a selective noble-metal-free molecular catalyst and carbon-based light-absorbing materials has recently emerged as a fruitful approach. In this work, we report about Co quaterpyridine complexes covalently linked to graphene surfaces functionalized by carboxylic acid groups. The nanostructured materials were characterized by X-ray photoemission spectroscopy, X-ray absorption spectroscopy, IR and Raman spectroscopies, high-resolution transmission electron microscopy and proved to be highly active in the visible-light-driven CO2 catalytic conversion in acetonitrile solutions. Exceptional stabilities (over 200 h of irradiation) were obtained without compromising the selective conversion of CO2 to products (>97%). Most importantly, complete selectivity control could be obtained upon adjusting the experimental conditions: production of CO as the only product was achieved when using a weak acid (phenol or trifluoroethanol) as a co-substrate, while formate was exclusively obtained in solutions of mixed acetonitrile and triethanolamine.

Plasmon Assisted Highly Efficient Visible Light Catalytic CO2 Reduction Over the Noble Metal Decorated Sr-Incorporated g-C3N4.

Abstract: The photocatalytic performance of g-C3N4 for CO2 conversion is still inadequate by several shortfalls including the instability, insufficient solar light absorption and rapid charge carrier’s recombination rate. To solve these problems, herein, noble metals (Pt and Au) decorated Sr-incorporated g-C3N4 photocatalysts are fabricated via the simple calcination and photo-deposition methods. The Sr-incorporation remarkably reduced the g-C3N4 band gap from 2.7 to 2.54 eV, as evidenced by the UV–visible absorption spectra and the density functional theory results. The CO2 conversion performance of the catalysts was evaluated under visible light irradiation. The Pt/0.15Sr-CN sample produced 48.55 and 74.54 µmol h−1 g−1 of CH4 and CO, respectively. These amounts are far greater than that produced by the Au/0.15Sr-CN, 0.15Sr-CN, and CN samples. A high quantum efficiency of 2.92% is predicted for the Pt/0.15Sr-CN sample. Further, the stability of the photocatalyst is confirmed via the photocatalytic recyclable test. The improved CO2 conversion performance of the catalyst is accredited to the promoted light absorption and remarkably enhanced charge separation via the Sr-incorporated mid gap states and the localized surface plasmon resonance effect induced by noble metal nanoparticles. This work will provide a new approach for promoting the catalytic efficiency of g-C3N4 for efficient solar fuel production. Highlights: 1 Noble metals (Pt, Au) decorated Sr-incorporated g-C3N4 photocatalysts are fabricated via facile calcination and photo-deposition methods.2 The optical absorption and charge separation properties of the photocatalysts are remarkably improved and the Pt/0.15Sr-CN photocatalyst exhibited excellent activity for CO2 conversion.3 A quantum efficiency of 2.92% is predicted for CO2 reduction over the Pt/0.15Sr-CN photocatalyst at 420 nm wavelength, which is accredited to the improved optical absorption and enhanced charge separation via Sr-incorporation and the surface plasmon resonance effect of noble metal nanoparticles.

Polymorphism in Squaraine Dye Aggregates by Self-Assembly Pathway Differentiation: Panchromatic Tubular Dye Nanorods versus J-Aggregate Nanosheets.

Abstract: A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes with a phenylene spacer unit. The aggregation behavior of this bis(squaraine) was investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into two supramolecular polymorphs with entirely different packing structures and UV/Vis/NIR absorption properties. The self-assembly pathway can be controlled by the cooling rate from a heated solution of the monomers. For both polymorphs, quasi-equilibrium conditions between monomers and the respective aggregates can be established to derive thermodynamic parameters and insights into the self-assembly mechanisms. AFM measurements revealed a nanosheet structure with a height of 2 nm for the thermodynamically more stable polymorph and a tubular nanorod structure with a helical pitch of 13 nm and a diameter of 5 nm for the kinetically favored polymorph. Together with wide angle X-ray scattering measurements, packing models were derived: the thermodynamic polymorph consists of brick-work type nanosheets that exhibit red-shifted absorption bands as typical for J-aggregates, while the nanorod polymorph consists of eight supramolecular polymer strands of the bis(squaraine) intertwined to form a chimney-type tubular structure. The absorption of this aggregate covers a large spectral range from 550 to 875 nm, which cannot be rationalized by the conventional exciton theory. By applying the Essential States Model and considering intermolecular charge transfer, the aggregate spectrum was adequately reproduced, revealing that the broad absorption spectrum is due to pronounced donor-acceptor overlap within the bis(squaraine) nanorods. The latter is also responsible for the pronounced bathochromic shift observed for the nanosheet structure as a result of the slip-stacked arranged squaraine chromophores.

Assembly Induced Super-Large Red-Shifted Absorption: The Burgeoning Field of Organic Near-Infrared Materials

Abstract: Supramolecular assembly of organic dye compounds with J-aggregation leads to a red-shifted absorption spectrum that greatly facilitates the construction of near-infrared (NIR) materials. A consider...

Effects of external electric and magnetic fields on the linear and nonlinear optical properties of InAs cylindrical quantum dot with modified Pöschl-Teller and Morse confinement potentials

Abstract: The theoretical investigation of linear and third-order nonlinear absorption coefficients and refractive index changes in the cylindrical quantum dot with two models of confinement potentials in axial direction, namely, modified Poschl-Teller and Morse potentials, and parabolic potential in radial direction, have been considered in the presence of external electric and magnetic fields. The selection rules for intraband transitions have been obtained for both potentials in the presence and absence of external fields. The behavior of linear, nonlinear and total absorption spectra have been observed for different values of temperatures for both potentials taking into account electron population on energy levels. The effect of change in the direction of electric field on the absorption spectra have been investigated, and the asymmetric and symmetric characters of these potentials manifest themselves differently: the peak positions of absorption lines for Morse potential undergo blue and red shifts compared to the case when the external electric field is absent, while for the case of modified Poschl-Teller potential the absorption lines have only red shift. The same dependencies have been obtained for refractive index changes for both potentials. The second and third harmonic generation coefficients as a function of the photon energy have been plotted both in the absence and presence of external fields.

Carboranealkynyl-Protected Gold Nanoclusters: Size Conversion and UV/Vis-NIR Optical Properties.

Abstract: Structure evolution has become an effective way to assemble novel monolayer-protected metal nanomolecules. However, evolution with alkynyl-stabilized metal clusters still remains rarely explored. Herein, we present a carboranealkynyl-protected gold nanocluster [Au28 (C4 B10 H11 )12 (tht)8 ]3+ (Au28 , tht=tetrahydrothiophene) possessing an open-shell electronic structure with 13 free electrons, which was isolated by a facile self-reduction method with 9-HC≡C-closo-1,2-C2 B10 H11 as the two-in-one reducing and protecting agent. Notably, Au28 undergoes a complete transformation in methanol into a stable and smaller-sized nanocluster [Au23 (C4 B10 H11 )9 (tht)6 ]2+ (Au23 ) bearing 12 valence electrons and crystal-field-like split superatomic 1D orbitals. The transformation process was systematically monitored with ESI-MS and UV/Vis absorption spectra. Au28 and Au23 both display optical absorption covering the UV/Vis-NIR range and NIR emission, which facilitates their potential application in the biomedical and photocatalytic fields.

Graphite Conjugation of a Macrocyclic Cobalt Complex Enhances Nitrite Electroreduction to Ammonia.

Abstract: This work reports on the generation of a graphite-conjugated diimine macrocyclic Co catalyst (GCC-CoDIM) that is assembled at o-quinone edge defects on graphitic carbon electrodes. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy confirm the existence of a new Co surface species with a coordination environment that is the same as that of the molecular analogue, [Co(DIM)Br2]+. GCC-CoDIM selectively reduces nitrite to ammonium with quantitative Faradaic efficiency and at a rate that approaches enzymatic catalysis. Preliminary mechanistic investigations suggest that the increased rate is accompanied by a change in mechanism from the molecular analogue. These results provide a template for creating macrocycle-based electrocatalysts based on first-row transition metals conjugated to an extreme redox-active ligand.

Conceptual-based design of an ultrabroadband microwave metamaterial absorber

Abstract: By introducing metallic ring structural dipole resonances in the microwave regime, we have designed and realized a metamaterial absorber with hierarchical structures that can display an averaged -19.4 dB reflection loss (∼99% absorption) from 3 to 40 GHz. The measured performance is independent of the polarizations of the incident wave at normal incidence, while absorption at oblique incidence remains considerably effective up to 45°. We provide a conceptual basis for our absorber design based on the capacitive-coupled electrical dipole resonances in the lateral plane, coupled to the standing wave along the incident wave direction. To realize broadband impedance matching, resistive dissipation of the metallic ring is optimally tuned by using the approach of dispersion engineering. To further extend the absorption spectrum to an ultrabroadband range, we employ a double-layer self-similar structure in conjunction with the absorption of the diffracted waves at the higher end of the frequency spectrum. The overall thickness of the final sample is 14.2 mm, only 5% over the theoretical minimum thickness dictated by the causality limit.

Ultra-wideband tunable metamaterial perfect absorber based on vanadium dioxide

Abstract: A dynamically adjustable ultra-wideband metamaterial perfect absorber (MPA) is proposed which consists of three resonance rings based on vanadium dioxide (VO2) and a metal ground layer separated by a dielectric spacer. The simulation results show that the terahertz (THz) absorption bandwidth of more than 90% absorptance reaches 3.30 THz, which covers from 2.34 to 5.64 THz, under different incident polarization angles. The range is better than that of previous VO2-based reports. Moreover, when the conductivity of VO2 changes from 200 S/m to 2×105 S/m, the absorption peak intensity can be adjusted continuously from 4% to 100%. The key is to optimize the geometric structure through interference cancellation and impedance matching theory, to achieve better absorption bandwidth and efficiency. Besides, the terahertz absorber has a wide-angle absorption effect both in TE and TM waves. Thus, the designed absorber may have many potential applications in modulating, sensing and imaging technology.

Schiff base-functionalized silatrane-based receptor as a potential chemo-sensor for the detection of Al3+ ions

Abstract: Excess Al3+ ions are considered toxic to living organisms Keeping the harmful effects of excess Al3+ metal ions in mind, a new Schiff base = functionalized silatrane as a potential chemo-sensor for the recognition of aluminium metal ions with high selectivity and specificity has been designed and well characterized using various characterization techniques such as IR, 1H NMR, 13C NMR, TGA, and mass spectroscopy The chemo-sensing properties were studied using ultraviolet and fluorescence spectroscopy The absorption spectrum of the synthesized receptor was changed only by the addition of Al3+ ions, while other ions showed negligible changes The 1 : 1 stoichiometric ratio of the chemo-sensor 4b with Al3+ was confirmed by Job's plot and linearity in the B–H plot The limit of detection observed for Al3+ ions was 2273 × 10−7 M and 98 × 10−9 M from ultraviolet and fluorescence spectroscopy, respectively The binding constant from the B–H plot and the Stern–Volmer quenching constant were found to be 02279 × 106 M−1 and 27 × 106 M−1, respectively These results explain the potential chemo-selectivity of the receptor 4b towards Al3+ metal ions, which may be useful for biological and industrial purposes

Broadband terahertz metamaterial absorber based on graphene resonators with perfect absorption

Abstract: The applications of terahertz waves and metamaterials in electromagnetic wave absorbers are one of the key focus areas of current interdisciplinary scientific research. In this study, we propose a metamaterial absorber composed of graphene double-open rectangular ring and graphene strip cross structures. The experiment uses numerical analysis software to study the proposed absorber. Transverse electric waves were normally incident on the absorber from the plane port, where resonance coupling was achieved. With an increase in the incidence angle alpha, the trough in the middle of the absorption spectrum continued to deepen. The bandwidth that the spectral absorption maintains above 0.9 is 2.88 GHz (1.260–1.548 THz). The maximum spectral absorption has reached 99.9%, which is approximately perfect absorption. The absorber under transverse magnetic wave incidence also exhibited a bandwidth advantage. As the Fermi energy continued to increase, the absorption bandwidth first increased and then decreased, and reached the maximum at ef = 0.5 eV. Simultaneously, the relative absorption bandwidth also reached its maximum. By adjusting the Fermi level of graphene, dynamic tuning of the metamaterial absorber could be achieved. Adjustment of the Fermi level shifted the absorption range and absorption bandwidth, and helped in controlling the increase in the relative absorption bandwidth. The findings of this study can be of theoretical and engineering significance in the domains of thermal photovoltaics, solar cells, and sensors, among others.

Experimental feasibility of molecular two-photon absorption with isolated time-frequency-entangled photon pairs

Abstract: Entangled photon pairs have promised to deliver a substantial quantum advantage for two-photon absorption spectroscopy. However, recent work has challenged the previously reported magnitude of quantum enhancement in two-photon absorption. We present a measurement of molecular absorption driven by isolated photon pairs using sum-frequency generation in a nonlinear optical crystal as a calibration device. We thereby establish an upper bound on the enhancement for entangled two-photon absorption in Rhodamine 6G, which lies well below previously reported values.

Narrow-band red-emitting phosphor with negligible concentration quenching for hybrid white LEDs and plant growth applications

Abstract: Narrow-band red-emitters are the key to solving problems encountered by the current white LED technology. In this context, a series of new red-emitting Li3BaSrLa3(MoO4)8:Eu3+ phosphors were synthesized and characterized through various spectroscopic methods. All phosphor compositions were crystallized in the monoclinic phase, with space group C2/c. A broad charge transfer (O2− → Mo6+) extended up to the blue region along with strong 7F0 → 5L6, 5D3 absorption, making them looked-for materials for warm white LED applications. The concentration quenching study reveals that there was no concentration-quenching occuring and the quantum yield of this non-concentration-quenching Li3BaSrLa0.3Eu2.7(MoO4)8 phosphor reaches 92.6%. The Li3BaSrLa0.3Eu2.7(MoO4)8 retain >80% of its emission intensity at 150 °C. The best red-emitting composition was integrated with near UV LED and obtained bright red emission with CIE x = 0.6647, y = 0.3357. White LED was fabricated by integrating the blue LED with yellow dye + red phosphor and white LED showed bright white light with CCT (5546 K), CIE (0.331, 0.385), and CRI (81%). In addition, the red LED spectrum is well-matched with the phytochrome (Pr) absorption spectrum and is useful for plant growth applications.

Numerical investigation of wideband L-shaped metasurface based solar absorber for visible and ultraviolet region

Abstract: A wideband metasurface absorber covering the visible to ultraviolet (UV) region (340 THz to 1150 THz) is numerically presented in this paper. The topmost layer consists of a periodic metallic array of L-shaped metasurface followed by a dielectric layer and thick metallic substrate. The nanostructure L-shaped metasurface array made up of tungsten material is used to enhance absorption spectra in the visible to the UV region. The average absorption resulted in an efficiency of 92.2% in the visible spectra (430 THz to 770 THz) and 73.6% absorption in the ultraviolet spectra (771 THz to 1150 THz). The absorption band has a close relationship with change in different parameters of the L-shaped metasurface absorber design is also investigated. The dual broadband achieves average absorption of more than 90% in visible region from 475 THz to 742 THz and in the ultraviolet region from 1010 THz to 1055 THz. The absorption is also investigated for inserted electromagnetic with different oblique incidence, which shows that the proposed absorber is achieving more than 80% absorption in-between 0° to 40° in the visible region from 470 THz to 750 THz. The presented broadband absorber is ultra-thin and single sized nanostructure can be used to scale large area photonics applications.

Engineering Ag-Nx Single-Atom Sites on Porous Concave N-Doped Carbon for Boosting CO2 Electroreduction.

Abstract: The electrochemical CO2 reduction reaction (CO2RR) offers an environmentally benign pathway for renewable energy conversion and further regulation of the environmental CO2 concentration to achieve carbon cycling However, developing desired electrocatalysts with high CO Faradaic efficiency (FECO) at an ultralow overpotential remains a grand challenge Herein, we report an effective CO2RR electrocatalyst that features Ag single-atom coordinated with three nitrogen atoms (Ag1-N3) anchored on porous concave N-doped carbon (Ag1-N3/PCNC), which is identified by X-ray absorption spectroscopy Ag1-N3/PCNC shows a low CO2RR onset potential of -024 V, high maximum FECO of 95% at -037 V, and high CO partial current density of 76 mA cm-2 at -055 V, exceeding most of the previous Ag electrocatalysts The in situ infrared absorption spectra technique proves that Ag1-N3 single-atom sites have sole linear-adsorbed CO and can easily desorb *CO species to achieve the highest CO selectivity in comparison with the corresponding counterparts This work provides significant inspiration on boosting CO2RR by tuning the active center at an atomic level to achieve a specific absorption with an intermediate