Increase In Absorption Cross Section Research Articles

CsPbX3 photoluminescence enhancement by localized surface plasmon of Ag nanoparticles

This paper investigates the enhanced photoluminescence of CsPbX3 by the localized surface plasmon (LSP) of Ag nanoparticles. The Ag nanoparticles with different sizes were obtained by annealing Ag thin films at different temperatures. Then the Ag/PMMA/perovskite structure was fabricated to realize the exciton-LSP coupling effect, and enhancement was found for wavelength-tunable CsPbX3 films. When the Ag film is heated to 200∘C, the maximum enhancement factor of LSP is 6.03. The LSP coupling effect induces the slight blue shift of the fluorescence emission center which is caused by the limitation of electron free trajectories under the LSP resonance frequency of Ag nanoparticles. As the gap between nanoparticles decreases, the absorption cross-section increases, and the scattering rate of electrons on the surface of metal nanoparticles greatly exceeds the internal scattering rate, causing the LSP resonance frequency to shift to the blue region, resulting in a blue shift of the PL spectrum.

Electronically defective tellurium-doped TiO2 catalysts for enhanced photoelectrochemical water splitting

Density functional theory (DFT) was employed to explore the effect of Tellurium substitutional (TeTi) doping in titanium dioxide (TiO2). The incorporation of Te was found to be favorable under O-rich conditions. Te doping resulted in band gap narrowing with the formation of mid-gap states, maintaining high dielectric constant, and reducing the birefringence of TiO2 in the UV region. The combination of TeTi with native oxygen vacancies (Ov) and hydrogen interstitials (Hi) was also studied. Band-gap narrowing was found to be prevalent in all structures, revealing their potential as good catalysts for photoelectrochemical water-splitting. The finite difference time domain (FDTD) analysis of 150-nm particle showed increased absorption cross-section over a wide band (up to ∼700 nm), better than that of Silicon at most wavelengths, and surpassing the performance of Hi without TeTi. Finally, the catalytic activity of the materials was investigated by studying the water-splitting intermediate reactions. In case of oxygen evolution reaction (OER), the TeTi + Ov material showed the best catalytic activity followed by the TeTi material. Whereas for the hydrogen evolution reaction (HER), the TeTi + Hi material was the best performing followed by the TeTi material, where the ΔGH was found to be −0.04 eV, close to the ideal 0 value and also has the closest d band center position to fermi level.

A novel approach in light-to-heat conversion: Cr3+-based photothermal agent

In response to the demands placed on functional materials for light-to-heat conversion applications, a new type of photothermal agent is proposed in this work. The proposed approach is based on inorganic materials heavily doped with Cr3+ ions. As shown, the increase in the probability of non-radiative processes and the increasing absorption cross-section of Cr3+ ions in GdAl3(BO3)4:Cr3+ observed with an increasing dopant ion concentration enabled significant optical heating of the sample. The proposed strategy exploiting Cr3+ ions, due to the much higher absorption cross-section of transition metal ions with respect to the lanthanide ions, may become an important alternative for currently used photothermal agents.

Nanocrystalline Yb:YAG-Doped Silica Glass with Good Transmittance and Significant Spectral Performance Enhancements.

In this study, Yb:YAG-nanocrystal-doped silica glass with high transmission and excellent spectral properties was successfully prepared using a modified sol–gel method. The X-ray diffraction (XRD), micro-Raman spectroscopy, electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM) analyses confirmed that the Yb:YAG nanocrystals, with their low content, homogeneous distribution, and small crystal size, directly crystallized into the silica glass network without annealing treatment. In contrast with conventional microcrystalline glass having large particles (>0.1 μm) and a large particle content, nanocrystalline glass with a homogeneous distribution and sizes of ~22 nm had higher optical transmittance and better spectral properties. Compared with Yb3+ doped silica glass without nanocrystals, the Yb:YAG-nanocrystal-doped silica glass had a 28% increase in absorption cross-section at 975 nm and a 172% enhanced emission cross-section at 1030 nm without any changes in the spectral pattern of the Yb3+ ions in the silica glass. Meanwhile, the Yb:YAG-doped silica glass with large size and high optical quality was easily prepared. Therefore, the Yb:YAG-nanocrystal-doped silica glass is expected to be a promising near-infrared laser material.

Utilizing Au–CuS heterodimer to intensify upconversion emission of NaGdF4:Yb/Er nanocrystals

Last decade has witnessed the unique ability of localized surface plasmon resonance nanostructure to significantly enhance upconversion luminescence efficiency of lanthanide ions, which has been demonstrated in terms of either increased absorption cross section or accelerated radiative decay rate (Purcell effect) induced by the concentrated electromagnetic field. Herein, we report the upconversion luminescence enhancement of NaGdF4:Yb/Er by dual plasmonic Au–CuS heterodimer nanocrystals, where both the local field enhancement effect and Purcell effect, initialized by different parts of the heterodimer, contribute jointly to the enhancement of upconversion emissions. This work provides the possibility to implement LSPR-based enhancement of upconversion luminescence by metal–semiconductor dual plasmonic antennas, where the judicious combination of active LSPR wavelengths can be manipulated via geometrical design of hetero-nanostructure.

Alloyed Heterostructures of CdSexS1–x Nanoplatelets with Highly Tunable Optical Gain Performance

Here, we designed and synthesized alloyed heterostructures of CdSexS1–x nanoplatelets (NPLs) using CdS coating in the lateral and vertical directions for the achievement of highly tunable optical gain performance. By using homogeneously alloyed CdSexS1–x core NPLs as a seed, we prepared CdSexS1–x/CdS core/crown NPLs, where CdS crown region is extended only in the lateral direction. With the sidewall passivation around inner CdSexS1–x cores, we achieved enhanced photoluminescence quantum yield (PL-QY) (reaching 60%), together with increased absorption cross-section and improved stability without changing the emission spectrum of CdSexS1–x alloyed core NPLs. In addition, we further extended the spectral tunability of these solution-processed NPLs with the synthesis of CdSexS1–x/CdS core/shell NPLs. Depending on the sulfur composition of the CdSexS1–x core and thickness of the CdS shell, CdSexS1–x/CdS core/shell NPLs possessed highly tunable emission characteristics within the spectral range of 560–650 nm. F...

Vortex energy flows generated by core-shell nanospheres.

Investigated in this paper is the interaction of light and the nanospheres composed by a dielectric core with a gold-shell cladding that causes the optical vortices inside the core and the whirlpools around the shell. Different radius ratios, dimensions and the dielectric functions of nanospheres were studied using the finite-difference time-domain method. It was found that optical vortices were most likely to occur in the regions of increased absorption cross section and reduced scattering cross section. Two optical vortices of the opposite polarity, each centered in one of the particles of a dimer are created by a nanoshell dimer. The surrounding media of a nanoshell with different dielectric functions can be used to affect the energy flows generated by core-shell nanospheres.

The Presence of the IsiA-PSI Supercomplex Leads to Enhanced Photosystem I Electron Throughput in Iron-Starved Cells of Synechococcus sp. PCC 7002.

Photosystem I (PS I) is highly demanding of iron, requiring 12 atoms in the bound FX, FB, and FA iron-sulfur clusters and two atoms in the mobile acceptor protein ferredoxin. When grown under iron-limiting conditions, certain cyanobacteria express IsiA, a peripheral chlorophyll a antenna protein, and IsiB, a flavodoxin that substitutes for ferredoxin. The IsiA protein forms single and double rings around PS I, presumably to increase the optical cross-section so as to compensate for fewer PS I complexes. Previous studies have shown that IsiA serves as an efficient light-harvesting structure ( Andrizhievskaya , G. G. ; et al. Biochim. Biophys. Acta 2002 , 1556 , 262 - 272 ); however, few, if any, studies have been carried out to show that the increased optical cross-section leads to an enhanced rate of electron transfer through PS I. Here, we report a more rapid transient accumulation of the A1(-) phyllosemiquinone anion radical by EPR spectroscopy in dark-adapted iron-depleted cells than in iron-replete cells after a block of intense light. A derivative-shaped optical signal in the light-minus-dark difference spectrum of PS I from an electrochromic bandshift of a carotenoid located near the A1 phylloquinones is enhanced in iron-depleted wild-type cells and in an iron-depleted isiB deletion strain, which lacks flavodoxin, but is greatly diminished in an iron-depleted isiA deletion strain, which lacks IsiA and flavodoxin. These findings indicate that the transient accumulation of electrons on A1 occurs more rapidly in the IsiA/PS I supercomplex than in the PS I complex alone. Thus, the increased absorption cross-section from the IsiA proteins translates directly to an enhanced rate of electron transfer through PS I.

1,4-二(4'- N , N -二苯胺基苯乙烯基)苯衍生物单双光子吸收性质的理论研究

With the development of two-photon microscopy, getting excellent two-photon fluorescence dyes become a hot topic. In this work, the equilibrium geometries, electronic structures, one- and two-photon absorption properties and the fluo- rescent emission properties for a series of D-π-A-π-D type 1,4-di(4'-N,N-diphenylaminostyryl)benzene (DPA-DSB) deriva- tives were investigated by the density functional theory (DFT). The results show that the one photon absorption wavelengths of this series of one-dimensional linear conjugated molecules are in the range 370~540 nm, fluorescence emission wave- lengths are in the range 435~700 nm, provided the absorption of the UV to green light and the emission of the all visible range. The Stokes shifts are in the 47~270 nm range. Thus, these molecules provide broad color fluorophore options mole- cules for biological fluorescence imaging and fluorescence microscopy. The response function approach has been used to calculate the two-photon properties. Analysis of two-photon properties of these molecules suggests that these molecules two-photon absorption wavelengths are at 650~880 nm. The molecules 2, 4, 5, 6, 8 and 12, 14 have two-photon absorption in the infrared light range, which means these molecules can be used as alternative molecules to design the infrared medical material. These molecules have the fluorescence signal in the visible range and excellent two-photon characteristics; can be used as two-photon fluorescent probes biomarkers and alternative materials. Analyzing its structure and optical properties indicate that the modification or replacement of the electron-withdrawing group in the center of the molecule can effectively shift its electronic spectrum, the addition of N atom or S atom can significantly improve the two-photon absorption cross-section. For the acetylenyl moiety as π bridge, if the molecular plane did not change compared with ethylene bridge, it makes the two-photon absorption cross-section decreases; if acetylene bridge improved the planarity of molecule, it causes two-photon absorption cross-section increases. This study aims to understand the relationship between molecular structure and two-photon properties and offer some important information for the design and synthesis of novel materials. Keywords DPA-DSB derivative; one-photon absorption; fluorescence emission; two-photon absorption; two-photon ab- sorption cross-section

Amplified spontaneous emission and lasing in colloidal nanoplatelets.

Colloidal nanoplatelets (NPLs) have recently emerged as favorable light-emitting materials, which also show great potential as optical gain media due to their remarkable optical properties. In this work, we systematically investigate the optical gain performance of CdSe core and CdSe/CdS core/crown NPLs having different CdS crown size with one- and two-photon absorption pumping. The core/crown NPLs exhibit enhanced gain performance as compared to the core-only NPLs due to increased absorption cross section and the efficient interexciton funneling, which is from the CdS crown to the CdSe core. One- and two-photon absorption pumped amplified spontaneous emission thresholds are found as low as 41 μJ/cm(2) and 4.48 mJ/cm(2), respectively. These thresholds surpass the best reported optical gain performance of the state-of-the-art colloidal nanocrystals (i.e., quantum dots, nanorods, etc.) emitting in the same spectral range as the NPLs. Moreover, gain coefficient of the NPLs is measured as high as 650 cm(-1), which is 4-fold larger than the best reported gain coefficient of the colloidal quantum dots. Finally, we demonstrate a two-photon absorption pumped vertical cavity surface emitting laser of the NPLs with a lasing threshold as low as 2.49 mJ/cm(2). These excellent results are attributed to the superior properties of the NPLs as optical gain media.

Molecular Orbital Engineering of a Panchromatic Cyclometalated Ru(II) Dye for p-Type Dye-Sensitized Solar Cells

We report a panchromatic cyclometalated Ru(II) complex, denoted as O18, which shows intense metal-to-ligand charge transfer transitions in the visible to near-IR region with the absorption tail extending to 800 nm. The panchromatic spectra response and enhanced molar extinction coefficient (ε = 1.9 × 104 M–1 cm–1 at 593 nm in solution) of O18 are attributed to the stabilization of the lowest unoccupied molecular orbital and the increased absorption cross section via rationally extending the π-conjugated system of 2,2′-bipyridyl (bpy) ligands. As a result, NiO solar cells sensitized with O18 show short-circuit currents up to 3.43 mA cm–2 and efficiencies up to 0.104%, which are the best among all cyclometalated-Ru(II)-sensitized p-type dye-sensitized solar cells. Femtosecond transient absorption spectroscopy reveals decreased geminate recombination across the O18–NiO interface by 1 order of magnitude compared to our previous report.

Encoding the Light-Sensitivity of Channelrhodopsin-2

Microbial rhodopsins are routinely used as light-controlled switches in neurobiology. Their versatile applicability relies on the simplicity of the optogenetic approach. Light-sensitivity is promoted to the host cell encoded in genetic information. However, the signal output is limited by the expression level and the molecular properties of the rhodopsins. The light-sensitivity of the system can set a limit for its usage. Different strategies might be envisaged how to tune and increase the responsiveness on a molecular level in the case of channelrhodopsin-2 (ChR2), a light-gated cation channel from Chlamydomonas reinhardtii: 1) increased absorption cross-section and quantum efficiency, 2) increased single channel conductance, 3) increased lifetime of the open state and 4) an amplification system. Here, we follow up the different strategies in a combined biophysical and neurobiological approach. As a first step we have developed the tools to study the different properties to have experimental access to the molecular properties from a spectroscopic and electrophysiological side. Especially, the development of fusing different rhodopsins into a single entity allows the discrimination between effects on the expression level and an increased single channel current by using one of the rhodopsins as a molecular ruler. In a next step we looked into the light-induced dynamical changes that accompany the photocycle of ChR2. This strategy allows us to map the conformational changes connected to the open state of the channel. We further generated a more calcium permeable mutant (CatCh, L132C) whose action on tuning the light sensitivity is different. Here, we propose a model that a local calcium concentration increase at the cytoplasmic membrane screens negative surface charges leading to a higher probability of opening the voltage-dependent sodium channels responsible for the onset of action potentials in neurons.

COMMENTS ON ABSORPTION CROSS-SECTION FOR CHERN–SIMONS BLACK HOLES IN FIVE DIMENSIONS

In this paper we study the effects of black hole mass on the absorption cross-section for a massive scalar field propagating in a five-dimensional topological Chern–Simons black hole at the low-frequency limit. We consider the two branches of black hole solutions (α = ±1) and we show that, if the mass of black hole increase the absorption cross-section decreases at the zero-frequency limit for the branch α = -1 and for the other branch, α = 1, the behavior is opposite, if the black hole mass increase the absorption cross-section increases. Also we find that beyond a certain frequency value, the mass black hole does not affect the absorption cross-section.

Near-infrared absorption properties of oxygen-rich stardust analogs

Several astrophysically relevant solid oxides and silicates have extremely small opacities in the visual and near-infrared in their pure forms. Datasets for the opacities and for the imaginary part k of their complex indices of refraction are hardly available in these wavelength ranges. We aimed at determining k for spinel, rutile, anatase, and olivine, especially in the near-infrared region. Our measurements were made with impurity-containing, natural, and synthetic stardust analogs. Two experimental methods were used: preparing small sections of natural minerals and synthesizing melt droplets under the electric arc furnace. In both cases, the aborption properties of the samples were measured by transmission spectroscopy. For spinel (MgAl2O4), anatase, rutile (both TiO2), and olivine ((Mg,Fe)2SiO4), the optical constants have been extended to the visual and near-infrared. We highlight that the individual values of k and the absorption cross section depend strongly on the content in transition metals like iron. Based on our measurements, we infer that k values below 10^(-5) are very rare in natural minerals including stardust grains, if they occur at all. Data for k and the absorption cross section are important for various physical properties of stardust grains such as temperature and radiation pressure. With increasing absorption cross section due to impurities, the equilibrium temperature of small grains in circumstellar shells increases as well. We discuss why and to what extent this is the case.

Exciton energy transfer between nanoparticles and nanowires

In this paper, we study the processes of exciton transfer in coupled nanoparticles and nanowires, and obtain convenient equations and numerical results for energy-transfer rates. For large distances, the energy-transfer rates are proportional to $1/{d}^{5}$, where $d$ is the nanoparticle-nanowire distance. Our models incorporate both semiconductor and metal material systems. In this paper, we show that excitonic energy generated optically in nanoparticles can be efficiently extracted and channeled to nanowires/nanotubes by utilizing the F\"orster energy-transfer mechanism. In particular, we propose a complex composed of an indirect-band semiconductor nanowire (silicon) and direct-band nanoparticles (CdTe). The efficiency of light harvesting in the CdTe-Si complex becomes strongly enhanced due to a strongly increased absorption cross section and a reduced absorption anisotropy. The system has potential for optoelectronic applications. Hybrid metal-semiconductor complexes have more efficient energy transfer and may be used for sensors. This paper describes available experimental data and suggests further experimental realizations.

Excitonic Coupling of Chlorophylls in the Plant Light-Harvesting Complex LHC-II

Manifestation and extent of excitonic interactions in the red Chl-absorption region (Q y band) of trimeric LHC-II were investigated using two complementary nonlinear laser-spectroscopic techniques. Nonlinear absorption of 120-fs pulses indicates an increased absorption cross section in the red wing of the Q y band as compared to monomeric Chl a in organic solution. Additionally, the dependence of a nonlinear polarization response on the pump-field intensity was investigated. This approach reveals that one emitting spectral form, characterized by a 2.3(±0.8)-fold larger dipole strength than monomeric Chl a, dominates the fluorescence spectrum of LHC-II. Considering available structural and spectroscopic data, these results can be consistently explained assuming the existence of an excitonically coupled dimer located at Chl-bindings sites a2 and b2 (referring to the original notation of W. Kühlbrandt, D. N. Wang, and Y. Fujiyoshi, Nature, 1994, 367:614–621), which must not necessarily correspond to Chls a and b) . This fluorescent dimer, terminating the excitation energy-transfer chain of the LHC-II monomeric subunit, is discussed with respect to its relevance for intra- and inter-antenna excitation energy transfer.

Photon-Enhanced Surface Dissociation Effects in Laser Photolysis of Amorphous Carbon from CH2I2

With near-UV Ar+-laser-induced photolysis of gaseous CH2I2, efficient, large-area or localized deposition of iodine-free amorphous carbon is possible at room temperature. The method allows a separate substrate heating and thereby a tuning of the deposits properties from soft and polymer-like to diamond-like. This article reports on an observed photon–surface interaction resulting in an enhanced carbon film formation. The shape of the deposit indicates that the deposition process is supported by an increased absorption cross section of surface-adsorbed intermediate molecular fragments, with respect to flat-angle surface-impinging photons.

PHOTON-ENHANCED SURFACE DISSOCIATION EFFECTS IN LASER PHOTOLYSIS OF AMORPHOUS CARBON FROM CH2I2

With near-UV Ar +-laser-induced photolysis of gaseous CH 2 I 2, efficient, large-area or localized deposition of iodine-free amorphous carbon is possible at room temperature. The method allows a separate substrate heating and thereby a tuning of the deposits properties from soft and polymer-like to diamond-like. This article reports on an observed photon–surface interaction resulting in an enhanced carbon film formation. The shape of the deposit indicates that the deposition process is supported by an increased absorption cross section of surface-adsorbed intermediate molecular fragments, with respect to flat-angle surface-impinging photons.

Set-up combining synchrotron radiation-induced photochemistry with IR probing: (HCl) n in Kr matrix

An FTIR spectrometer samples with an optimized beam guiding optics the volume irradiated with VUV radiation from a high flux beamline and monitors photochemical reaction products. Additionally UV and visible fluorescence spectra are recorded. Dissociation efficiencies for HCl monomers and multimers in Kr matrix are rather similar. The increase in absorption cross-section with multimer size is compensated by a decreasing dissociation quantum efficiency. The H atom cage exit probability of monomers is only some percent in contrast to previous results, and the discrepancy is attributed to saturation effects in fluorescence spectroscopy of electronic transitions in the Cl products. Build-up and decay of Cl–HCl and H–HCl intermediates are monitored and simulated.

Electronic equilibria and electron delocalization

The normal reflectivity of Ti4O7 (T = 290 K) is measured in the range of 0.1 to 3 eV. The reflectivity shows a minimum which corresponds to the collective resonance of all Ti3+ valences. The optical absorption as calculated from the diffuse reflectivity of Ti4O7 is investigated in the spectral range of 0.5 to 2.5 eV and at temperatures between 10 and 300 K. A broad asymmetrical absorption band with a maximum at about 0.7 eV and an absorption sideband at about 1.5 eV is observed. The overall line shape is explained by the polaronic absorption mechanism. From room temperature down to the metal-insulator transition at T>m ≈ 150 K the total polaronic absorption cross section remains constant. It drops down in the intermediate phase (125–150 K) and then increases with decreasing temperature below the Verwey transition at Tv ≈ 125 K. The increasing absorption cross section below Tv as well as the shift of the peak position to lower energy is in accordance with the gap opening at ≈ 0.2 eV previously reported (Kaplan et al. [1]) and is explained by the separation of single polaronic from bipolaronic energy levels. The magnetic susceptibility of Ti4O7 is discussed with respect to an exchange pairing mechanism above and below Tm. It is suggested that a melting of the bipolaronic state during the metal-insulator transition results in a fluctuating valence bond system above Tm.