High Absorption Cross Section Research Articles

Fluorescence Quantum Yield and Single-Particle Emission of CdSe Dot/CdS Rod Nanocrystals

The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY.

A Frequency Domain Control Perspective on Xenon Resistance for Load Following of Thermal Nuclear Reactors

Xenon (Xe) is a noble gas with an isotope (Xe-135) that has an extremely high absorption cross section of neutrons moving at thermal energies. Xe-135 is produced through a chain of decay of isotopes resulting from nuclear fission, in addition to directly resulting from fission. The decay chain results in a phase lag between Xe-135 concentration and the neutron flux or power in a nuclear reactor. The phase lag results in oscillations and several hours of delay between the set power and the response power of a reactor. To enable rapid load following of reactors to a maximum of one change per hour, or a frequency of $2.7\times 10^{-4}$ Hz ( $1.74\times 10^{-3}$ rad/s), a Bode-step controller is designed to expand the functional bandwidth of the reactor and to stabilize the control loop. The resulting controller is capable of projecting the Xe-135 concentrations and providing a phase lead to overcome the inherited phase lag. The controller was found to eliminate the power oscillation and enable the targeted “one change per hour” power set point change.

An IBBCEAS system for atmospheric measurements of glyoxal and methylglyoxal in the presence of high NO<sub>2</sub> concentrations

Abstract. A system based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) has been developed for simultaneous measurement of nitrogen dioxide (NO2), glyoxal (GLY), and methylglyoxal (MGLY). In this system, the measured light absorption at around 460 nm is spectrally resolved. The concentration of absorbers is determined from a multicomponent fit. At an integration time of 100 s, the measurement sensitivity (2σ) for NO2, GLY, and MGLY is 18, 30, and 100 ppt, respectively. The measurement uncertainty, which mainly originates from path length calibration, sampling loss, and uncertainty of absorption cross sections is estimated to be 8 % for NO2, 8 % for GLY, and 16 % for MGLY. When deploying the instrument during field observations, we found significant influence of NO2 on the spectra fitting for retrieving GLY and MGLY concentrations, which is caused by the fact that NO2 has a higher absorption cross section and higher ambient concentration. In order to minimize such an effect, a NO2 photolytic convertor (NPC), which removes sampled NO2 at an efficiency of 76 %, was integrated on the IBBCEAS system. Since sampled GLY and MGLY are mostly (≥95 %) conserved after passing through the NPC, the quality of the spectra fitting and the measurement accuracy of ambient GLY and MGLY under NO2-rich environments could be improved.

Utilizing niobium plasmonic perfect absorbers for tunable near- and mid-IR photodetection.

With the fast development of single photon-based technologies such as quantum computing and quantum cryptography, conventional avalanche photodiodes as single photon detectors are not the optimum tools anymore. They are currently replaced by Superconducting Nanowire Single Photon Detectors (SNSPDs) based on the superconducting to normal conducting phase transition. The current challenge with SNSPDs lies in overcoming the trade-off between detection efficiency and recovery time. While a large active area will lead to high detection efficiency, the associated high kinetic inductance causes a long recovery time. Plasmonic effects can play an important role in the absorption enhancement of SNSPDs. Nanostructuring with a suitable geometry can provide a high-absorption cross-section at the intrinsic nanowire surface plasmon resonance, which can be significantly larger than their geometric cross-section. We present a photodetector based on the intrinsic localized surface plasmon resonance of a niobium nanowire, which is one of the common superconductors with low kinetic inductance. Additionally, we are increasing the absorption of our nanostructures even further using a plasmonic perfect absorber scheme. We fabricated a plasmonic perfect absorber superconducting photodetector, investigated its response to external light at resonance, and proved its plasmonic behavior as evidenced by its polarization dependence.

Carbonaceous matter in glacier at the headwaters of the Yangtze River: Concentration, sources and fractionation during the melting process

Carbonaceous matter has an important impact on glacial retreat in the Tibetan Plateau, further affecting the water resource supply. However, the related studies on carbonaceous matter are still scarce in Geladaindong (GLDD) region, the source of the Yangtze River. Therefore, the concentration, source and variations of carbonaceous matter at Ganglongjiama (GLJM) glacier in GLDD region were investigated during the melting period in 2017, which could deepen our understanding on carbonaceous matter contribution to glacier melting. The results showed that dissolved organic carbon (DOC) concentration of snowpit samples (283 ± 200 μg/L) was much lower than that of precipitation samples (624 ± 361 μg/L), indicating that large parts of DOC could be rapidly leached from the snowpit during the melting process. In contrast, refractory black carbon (rBC) concentration measured by Single Particle Soot Photometer of snowpit samples (4.27 ± 3.15 μg/L) was much higher than that of precipitation samples (0.97 ± 0.49 μg/L). Similarly, DOC with high mass absorption cross-section measured at 365 nm value was also likely to enrich in snowpit during the melting process. In addition, it was found that both rBC and DOC with high light-absorbing ability began to leach from the snowpit when melting process became stronger. Therefore, rBC and DOC with high light-absorbing ability exhibited similar behavior during the melting process. Based on relationship among DOC, rBC and K+ in precipitation, the main source of carbonaceous matter in GLJM glacier was biomass burning during the study period.

Computational and experimental comparison of boron carbide, gadolinium oxide, samarium oxide, and graphene platelets as additives for a neutron shield

Neutron shielding materials are used in aerospace, space, medical, and nuclear applications and there is a growing need of neutron shielding materials with increased temperature resistance. This is difficult to achieve with the current approach of using borated or lithium enriched polyethylene or polyamide composites because their hydrogen content limits temperature resistance to 200 °C. To address this challenge, an elastomer-based neutron shielding material has been developed with a degradation temperature greater than 300 °C and a macroscopic neutron cross section better than that of 5% borated polyethylene. By compensating for the low number of hydrogen atoms in this material, compared to polyethylene or polyamides, iron and additives with a high neutron absorption cross section such as gadolinium and samarium are incorporated to achieve the necessary attenuation properties. Graphene platelets were also added to evaluate graphene's ability to mitigate secondary gamma from the neutron absorption by gadolinium and samarium. A computational study was first completed in Monte Carlo N-Particle (MCNP) to benchmark existing materials and compare the loading of the potential additives. The maximum experimental fast neutron cross-sections for each absorber additive were 0.021 cm−1 in 9% B4C, 0.031 cm−1 with 27% Gd2O3, and 0.030 cm−1 with 3% Sm2O3 compared to only 0.023 cm−1for 5% borated polyethylene. The sample containing 10% Gd2O3 and 2% B4C attenuated neutrons better than the borated polyethylene with a fast neutron cross section of 0.026 cm−1 and exhibited the lowest amount of secondary gamma photons of all the material combinations.

A "Multi-Heavy-Atom" Approach toward Biphotonic Photosensitizers with Improved Singlet-Oxygen Generation Properties.

Two trispicolinate 1,4,7-triazacyclonane (TACN)-based ligands bearing three picolinate biphotonic antennae were synthetized and their Yb3+ and Gd3+ complexes isolated. One series differs from the other by the absence (L1 )/presence (L2 ) of bromine atoms on the antenna backbone, offering respectively improved optical and singlet-oxygen generation properties. Photophysical properties of the ligands, complexes and micellar Pluronic suspensions were investigated. Complexes exhibit high two-photon absorption cross-section combined either with NIR emission (Yb) or excellent 1 O2 generation (Gd). The very large intersystem crossing efficiency induced by the combination of bromine atom and heavy rare-earth element was corroborated with theoretical calculations. The 1 O2 generation properties of L2 Gd micellar suspension under two-photon activation leads to tumour cell death, suggesting the potential of such structures for theranostic applications.

Determination of Two-Photon Absorption Cross-Sections in Selected Diketo-Pyrrolo-Pyrroles

The paper deals with determination of two-photon absorption cross-sections of selected representatives of diketo-pyrrolo-pyrrole. The materials were optimized in order to test the influence of various substitutions on the diketo-pyrrolo-pyrrole basic molecule. The two-photon absorption cross-sections were determined using two-photon excited fluorescence technique. A considerably high two-photon absorption cross-section in order of 1000 GM was found for non-symmetrically substituted derivative with donor-acceptor structure. All of the derivatives showed strong fluorescence in solid state visible by naked eye. These results demonstrate that this class of materials can be used in e.g. two-photon fluorescence microscopy in the form of nanoparticles.

Resonance Energy Transfer in Hybrid Plasmonic-Polymetallophthalocyanine Nanoantennas Fabricated By Electropolymerization

Metal nanoparticles have exceptionally high photon absorption cross-sections at energies that excite a localized surface plasmon resonance compared to non-metallic particles. The light energy absorbed by these metal “nanoantennas” can be transferred non-radiatively to a coupled semiconductor material. The energy is stored in the semiconductor as electron-hole pairs through the dephasing of localized surface plasmon dipoles. The electrons and holes can then be extracted for charge transfer applications, such as catalysis. Here, we show that individual gold nanorods can be selectively coated via electropolymerization with metallophthalocyanines, a well-established class of oxygen and carbon dioxide reduction catalysts, to produce hybrid plasmonic-polymeric nanoantennas. The semiconducting polymer coatings have a high density of π-π* dipole transitions with energies matching the dipole resonance energy of the gold nanorods, enabling efficient dipole-dipole coupling. Using in situ hyperspectral dark-field imaging, we observed large plasmon resonance linewidth increases in the scattering spectra of single gold nanorods with the anodic deposition of the polymer coating, and attribute this to a greatly decreased plasmon dephasing time due to resonance energy transfer. In situ single particle spectroscopy was required to reveal that the increase in resonance linewidth was dependent on the polymer thickness and the energy of the uncoated gold nanorod longitudinal plasmon resonance. Permeable metallophthalocyanine polymer coatings are spectroscopically and chemically tunable, and have a high effective surface area opening up new opportunities for plasmonic antenna-reactor electrodes in energy sustainability applications.

Solvatochromic Near-Infrared Probe for Polarity Mapping of Biomembranes and Lipid Droplets in Cells under Stress.

Can polarity-sensitive fluorescent dyes monitor the response of live cells to fundamental stress conditions, such as deprivation from nutrition and oxidative stress? To address this question, we developed a push-pull dioxaborine probe (DXB-NIR) for biomembranes and lipid droplets featuring strong solvatochromism in the far-red to near-infrared region, high fluorescence brightness, photostability, and two-photon absorption cross section, reaching 13800 GM at 930 nm. In model membranes, DXB-NIR exhibits unprecedented 80 nm shift between liquid ordered and disordered membrane phases, allowing robust imaging of separated membrane microdomains. Two-color imaging of live cells with DXB-NIR enables polarity mapping in plasma membranes, endoplasmic reticulum, and lipid droplets, which reveals that starvation and oxidative stress produce an increase in the local polarity, and this change is different for each of the studied cell compartments. Thus, by pushing the limits of existing solvatochromic dyes, we introduce a concept of polarity mapping for monitoring the response of cells to stress.

Boron-10 effect on the reactivity of the IPR-R1 Triga research reactor

The isotope boron-10 (B-10) has a high thermal neutron absorption cross-section and is used to poison the chain reaction in some light-water reactors (chemical shim). The purpose of this work was to show the effectiveness of boron as a neutron absorber in controlling the reactivity of nuclear reactors cooled by light water. In this way, samples were placed in sealed containers with various concentrations of boric acid in the IPR-R1 Triga nuclear research reactor core. Thus, the reactivity variation of this reactor was determined. The sample characterization was performed before and after the experiments by the measurement of pH and electrical conductivity. The IPR-R1 reactor is located at the Nuclear Technology Development Center (CDTN) in Belo Horizonte, Brazil. Variations of reactivities were evaluated using the static reactivity null method and the dynamic method. The results obtained made it possible to simulate B-10 consumption during the operation of a reactor and its effect on reactivity with increasing boric acid concentrations. The pH values showed small increases after irradiation and their conductivities showed minor changes. As a result of this experiment, a correlation was drawn between various boric acid concentrations and reactor reactivity.

Highly photostable two-photon NIR AIEgens with tunable organelle specificity and deep tissue penetration

Photostability is a particularly important parameter for fluorescence imaging especially long-term dynamic tracking in live samples. However, many organic fluorophores show poor photostability under one-photon and two-photon continuous irradiation. In addition, these traditional fluorophores also suffer from aggregation-caused quenching (ACQ) in aggregate state in insolvable water environment. Therefore, it remains challenging to develop photostable and ACQ-free fluorophores for biological imaging. In this work, we developed two highly photostable aggregation-induced emission luminogens (AIEgens) based on the cyanostilbene core for in vitro and ex vivo bioimaging. These AIEgens named CS-Py+SO3− and CS-Py+ exhibit near-infrared solid-state emission, large Stokes shift (>180 nm), high fluorescence quantum yield (12.8%–13.7%) and good two-photon absorption cross section (up to 88 GM). CS-Py+SO3− and CS-Py+ show specific organelle staining with high biocompatibility in membrane and mitochondria in live cells, respectively. In addition, selective two-photon mitochondria visualization in live rat skeletal muscle tissues with deep-tissue penetration (about 100 μm) is successfully realized by using CS-Py+. Furthermore, these AIEgens especially CS-Py+ exhibit remarkably high resistance to photobleaching under one-photon and two-photon continuous irradiation. These highly photostable AIEgens could be potentially utilized in visualizing and tracking specific organelle-associated dynamic changes in live systems.

PMAO coated Na(Gd0.5Lu0.5)F4:Nd3+ nanocrystals as multifunctional contrast agent with NIR optical, X-ray and magnetic imaging properties

Nanomaterials with multiple imaging functionalities are nowadays getting tremendous attention due to their several superior features compared to existing contrast agents. By developing a nanomaterial that exhibit multiple functionalities, the possibility to increase the amount of imaging information obtained in a short amount of time is becoming more and more a reality. In this work, we developed a multifunctional nanocrystals (NCs), Na(Gd0.5Lu0.5)F4:Nd3+, that combines multiple rare-earth features as an all-in-one imaging agent comprised of optical imaging, magnetic imaging, and X-ray imaging by utilizing the superparamagnetic features of Gd3+, the high X-ray absorption cross section of Lu3+, and the NIR fluorescence of Nd3+. Morphology, optical properties, and cell viability are shown in detail where the utility of this multifunctional imaging agent was confirmed by optical, X-ray and magnetic imaging experiments. Surface functionalization of the NCs is also presented to highlight the potential application of the NCs as contrast agents in biological imaging.

Triplet-Sensitization by Lead Halide Perovskite Thin Films for Near-Infrared-to-Visible Upconversion

Lead halide-based perovskite thin films have attracted great attention due to the rapid increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet–triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross-sections throughout the visible spectrum, and the strong spin–orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the passivating ligands required for colloidal sensitizers, which can hinder exciton transport through large scale arrays and reduce the triplet transfer effic...

On the use of organic ligands to sensitize inorganic phosphors for ultraviolet, visible, and infrared light harvesting

In the last decade, numerous research efforts have been focused on the use of wavelength-converting materials to extend the spectral response of existing solar cell technologies. In this regard, lanthanide-based nanophosphors are promising candidates with their emissions ranging from the UV to near-infrared. Nevertheless, new challenges are raised for the engineering, design, and synthesis of lanthanide phosphors with a high absorption cross section to match the wavelengths of solar cells spectral sensitivity. One creative approach involves the coordination of organic ligands at the nanophosphors surface to broaden their excitation wavelength range and yield ultrabright highly efficient hybrid phosphors. Herein, the state-of-the-art of the sensitization of inorganic lanthanide-based phosphors with organic antennas that could be used to enhance the performance of a-Si and c-Si solar cells through downshifting, upconversion, and downconversion mechanisms is briefly reviewed.

Rationally designed azobenzene photoswitches for efficient two-photon neuronal excitation

Manipulation of neuronal activity using two-photon excitation of azobenzene photoswitches with near-infrared light has been recently demonstrated, but their practical use in neuronal tissue to photostimulate individual neurons with three-dimensional precision has been hampered by firstly, the low efficacy and reliability of NIR-induced azobenzene photoisomerization compared to one-photon excitation, and secondly, the short cis state lifetime of the two-photon responsive azo switches. Here we report the rational design based on theoretical calculations and the synthesis of azobenzene photoswitches endowed with both high two-photon absorption cross section and slow thermal back-isomerization. These compounds provide optimized and sustained two-photon neuronal stimulation both in light-scattering brain tissue and in Caenorhabditis elegans nematodes, displaying photoresponse intensities that are comparable to those achieved under one-photon excitation. This finding opens the way to use both genetically targeted and pharmacologically selective azobenzene photoswitches to dissect intact neuronal circuits in three dimensions.

Absorption of light in a single vertical nanowire and a nanowire array

Both a single III–V semiconductor nanowire and an array of such nanowires have shown promise for solar cell applications. However, the correspondence between the optical properties of the single nanowire and the nanowire array has not been studied. Here, we perform electromagnetic modeling of InP nanowires to study this relationship. We find that a single nanowire can show at an absorption peak, a remarkably high absorption cross-section that is more than 50 times the geometrical cross-section. With optimization of the diameter of the single nanowire, the short-circuit current density is 30 times higher than in a bulk solar cell. With such a strong absorption, we predict an apparent efficiency >500% for the single nanowire solar cell. In contrast, we show that an efficient nanowire array solar cell cannot rely on strong absorption just through the absorption peak. Instead, the nanowires need to be packed rather closely to enhance the absorption of the full solar spectrum. At the optimum diameter for the nanowire array, neighboring nanowires compete strongly for absorption of incident photons at the absorption peak, which limits the absorption per nanowire by a factor of 18. As a result, the single InP nanowire is optimized at a diameter of 110 nm while the nanowires in the array are optimized at a considerably larger diameter of 180 nm. Importantly, we show analytically the coupling efficiency of incident light into the fundamental HE11 guided mode and consecutive absorption of the mode in the nanowires. With that analysis, we explain that a single nanowire shows two different absorption pathways—one through coupling into the guided mode and another by coupling into the nanowire through the sidewall. This analytical analysis also shows at which period the neighboring nanowires in an array start to compete for absorption of incident photons.

Effect of symmetric and asymmetric substitution on the optoelectronic properties of 9,10-dicyanoanthracene

Six newly synthesised 9,10-dicyanoanthracene derivatives exhibit high two-photon absorption cross sections particularly upon symmetric substitution with strong electron donors.

Two-photon absorption properties of BODIPY-like compounds based on BF2-naphthyridine complexes.

Boron dipyrromethene type molecules (BODIPYs) are versatile molecules which have been used for applications ranging from photodynamic therapy to solar cells (DSSC). However, these molecules usually do not present high two-photon absorption cross-sections, limiting their use in nonlinear optical applications. Herein, we study a series of BF2-naphthyridine based boron-complexes with electron-donating and withdrawing groups to increase their two-photon absorption. We have found two-photon absorption cross-sections up to approximately 270 GM, which corresponds to an increase of approximately five times in comparison to the average cross-section value reported for molecules with similar conjugation length, indicating such compounds as potential materials for nonlinear applications in both the visible and infrared spectral regions.

Searching for the optimum number of integral burnable absorber rods used in PWR assembly

This article discusses the effect of different Integral Burnable Absorber numbers (IBAs) on the neutronic characteristics of a Pressurised Water Reactor (PWR) to provide a suitable safety level. MCNPX code version 2.6 was used to design a three dimensional model for PWR assembly. The designed model has been validated by comparing the output values of the infinity multiplication factor (Kinf) with a previously published value. The designed MCNPX model was used to analyse the radial distribution of thermal neutrons and the power through PWR assembly with and without IBA. Due to the high absorption cross-section of gadolinium, it has been used as a burnable absorber material in the IBA rods. The gadolinium isotopes suppressed the power in the regions where they were distributed. The existence of IBA rods has a large effect on the Kinf. This effect decreases gradually with burnup due to the degradation of gadolinium. The gadolinium isotopes degradation was analysed with burnup. Different numbers of IBA rods were investigated to optimise the suitable number that can be used in the PWR assembly. The reactivity has been investigated at different numbers of IBAs. The gadolinium effect on the concentration of 135Xe and 149Sm resulting from the fission process was analysed.