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Previous modeling studies have not properly explained the measured mass absorption cross section (MAC) at 550 nm, the linear backscattering depolarization ratio (LDR) at 355 and 532 nm, and the scattering matrix of soot at 532 nm. In this work, we attempt to use a black carbon (BC) model with an intrinsic organic carbon (OC) coating to explain the large MAC, large LDR, and measured scattering matrix. Our results show that the bare fractal BC model is not able to explain MAC, LDR, and scattering matrix simultaneously and that the modeling values do not cover the measurement range. This study shows that the modeled LDR and scattering matrix can cover the measurement range if we constrain the MAC of the BC in the measurement range by the intrinsic OC coating when we consider the effects of monomer radius, monomer number, and monomer overlap simultaneously. Therefore, intrinsic OC coating can be a significant source of uncertainty in the optical properties of fresh soot. Plain Language Summary: Since soot is the most important absorbing particle in the atmosphere, an accurate calculation of the optical properties of soot is of great importance for climate assessment and remote sensing. However, some of the observed optical properties of soot are difficult to explain with current models. In this study, a black carbon (BC) model with an intrinsic organic carbon (OC) coating is used to explain these difficult‐to‐explain optical properties. The results show that the simulated mass absorption cross section (MAC), linear backscattering depolarization ratio (LDR), and scattering matrix are difficult to explain when only the influence of BC is considered, although the effects of monomer size, monomer number, and monomer overlap are taken into account. Range of observation. However, after accounting for the intrinsic OC coating, the model is able to account for the range of realistic optical observations. Therefore, the intrinsic OC coating may be responsible for some optical properties that are difficult to explain with the current models. Key Points: The model of pure black carbon (BC) has difficulty explaining some optical observations of sootWe have proposed a soot model consisting of a BC core and an intrinsic organic carbon (OC) shellThe intrinsic OC coating may be a cause of some unexplained optical properties in current models [ABSTRACT FROM AUTHOR]

Ytterbium ion doped calcium niobium gallium garnet crystal (Yb: Ca3 (NbGa)5 O12) was successfully grown by Bridgman method. The structure of the crystal was analyzed by XRD. The crystal is cubic crystal system, and the unit cell parameter a = b = c = 12.471 Å. The crystal was tested by Raman spectroscopy, transmission spectroscopy, absorption and emission spectroscopy, and fluorescence lifetime. The absorption cross section, emission cross section, and gain cross section of the crystal were calculated. The effects of annealing in air on the absorption spectrum, emission spectrum and fluorescence lifetime of the crystal were studied. The absorption cross section at 935 nm before annealing is 1.82 x 10-20 cm², and it decreases to 1.40 x10-20 cm² after annealing. The emission cross section at 1 031 nm before annealing is 0.56 x10-20 cm² and it decreases to 0.40 x 10-20 cm² after annealing. The fluorescence decay time before annealing is 1.42 ms, and it is 1.32 ms after annealing. The results demonstrate that the annealing of Yb:Ca3 (NbGa)5 O12 single crystal in air will adversely affect the laser performance of the crystal.Yb:Ca3(NbGa)5O12 crystal. [ABSTRACT FROM AUTHOR]

Oxyfluoride transparent glass‐ceramics (GC) are widely used as the matrix for rare‐earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt‐quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si‐based photo‐resistor,a solar‐blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar‐blind UV detectors. [ABSTRACT FROM AUTHOR]

The nonlinear optical limiting (OL) property of tin phthalocyanine porous organic frameworks (Sn-Pc-POFs) dispersion in the nanosecond regime was studied, which showed excellent dispersibility and stability as well as a low OL threshold. To clarify the nonlinear optical response mechanisms in the material, the energy level structure of Sn-Pc-POFs was simulated using the density functional theory calculation, and the photoinduced carrier dynamics was studied using femtosecond time-resolved transient absorption spectroscopy. The results indicated that the large absorption cross section and long lifetime of the excited state were responsible for the excellent OL property of the material. [ABSTRACT FROM AUTHOR]

Oxazolones or azlactones are small heterocyclic systems that can be easily functionalized with a double bond directly attached to their structure. In addition, they can be substituted on the opposite side of the heterocycle with styrenyl groups to extend their conjugation. This allows for versatile tuning of their linear and non‐linear optical properties. In this work, eight doubly substituted oxazolones including different push‐pull or pull‐pull designs were synthesized, and their linear and non‐linear photophysical properties were studied. As we show, the two‐photon activity of these systems is dependent on the donor‐acceptor pattern, where a methoxy substitution on the styrene end of the molecule and an acetyl group on the other end shows two‐photon Z‐E conversion properties with an important two photon absorption cross section of 308 GM. Most oxazolones shown in this study undergo picosecond relaxation to the electronic ground state, releasing the biphotonic energy to their surrounding environment. The results obtained in this work are indicative of potential applications of these molecules in schemes where high spatial patterning or thermalization is required. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the different properties of cobalt-doped and undoped tin oxide thin films. The tin oxide thin films were doped with different atomic percentages of cobalt, ranging from 0% (undoped) to 2% and 4%, using a cost-effective and easily accessible technique known as spray pyrolysis with a moving nozzle at 490 °C. The phase identification of the different thin layers was carried out using X-ray diffraction, which indicated that the compound is homogeneous has a polycrystalline structure and is, with preferential orientation growth at the (211) level. The optical properties of the synthesized thin films were investigated using UV-visible spectroscopy in the range from 300 to 900 nm, which allowed the estimation of both linear and nonlinear optical properties. The results of the investigations into the linear optical properties indicated that the samples have a direct band gap energy between 3.75 to 3.81 eV, permittivity between 2.67 to 3.266, photoelectrons between 0.2 to 3.35 = 1025, and refractive index between 1.778 to 1.875. The results also indicated that the absorption cross section changes with photon energy and the number of photoelectrons, where it has an approximately constant value at low energies. Moreover, the nonlinear optical properties were determined using the Sheik-Bahae model, which revealed that the samples have the same maximum two-photon absorption (TPA) process coefficient of 3.63 cm/W and the same maximum nonlinear refractive index (NRI) value of 6.91 × 10−8 cm2/W. [ABSTRACT FROM AUTHOR]

The development of fluorescent probe for hydrazine (N2H4) detection has attracted much attention due to the important role of N2H4 plays in the fields of medicine, agriculture, biology and environments. In this paper, the optical properties and water solubility of two novel two-photon fluorescent molecular probes (Probe1 and Probe2) before and after the reaction with N2H4 are studied by using the density function theory. The results show that electronic distribution and transition dipole moment of the probes are obviously changed after the reaction with N2H4, thus the optical properties of the molecules are influenced and the detection of N2H4 are realized. In addition, photoinduced electron transfer processes for Probe1 and Probe2 in the presence of N2H4 are theoretically characterized, which explains the experimental observations from the microscopic mechanism. Special attention has been paid on the analysis of the two-photon absorption for the probes with the absence and presence of N2H4 by the response theory method. Both probes with good water solubility show large variation on the two-photon absorption cross section when reacts with N2H4. In particular, the two-photon absorption response of Probe2 is more obvious, so it possesses preferable two-photon fluorescence microscopic imaging ability. More importantly, the receptor effect on the sensing performances of the probes are demonstrated, providing a theoretical reference for the design and synthesis on more efficient two-photon fluorescence N2H4 probes. Our study provides necessary information on the response mechanism of the studied chemosensors and helps to establish the relationship between the structure and optical properties of two-photon fluorescence N2H4 probes. [ABSTRACT FROM AUTHOR]

In this paper, a series of Er∶CaGdAlO4 (Er∶CGA) laser crystals with different Er3 + doping concentrations (molar fraction) were grown by laser-heated pedestal growth method. The optical properties of the prepared series crystals were studied in detail. The maximum absorption coefficient, absorption cross section, full width at half maximum and radiation lifetime at the range of 780 ~ 840 and 955 ~ 1 020 nm in the absorption spectra were compared by combining the J-O theoretical calculation and optical characterization. In addition, the optical performance parameters of fluorescence emission spectrum such as emission intensity, emission cross section and energy level fluorescence lifetime were characterized and futher calculated. As a result, the optimal doping concentration of Er3 + is 5%. This work provides a certain experimental basis for obtaining a new type of laser gain medium which is expected to be used in 1. 5 ~1. 7 μm near-infrared band all-solidstate laser. [ABSTRACT FROM AUTHOR]

Comparing the performance of molecular and nanoscale luminophores and luminescent micro- and nanoparticles and estimating achievable signal amplitudes and limits of detection requires a standardizable intensity scale. This initiated the development of the relative MESF (number of molecules of equivalent soluble fluorochromes) and ERF (equivalent reference fluorophores) scales for flow cytometry and fluorescence microscopy. Both intensity scales rely on fluorescence intensity values assigned to fluorescent calibration beads by an intensity comparison to spectrally closely matching fluorophore solutions of known concentration using a spectrofluorometer. Alternatively, the luminophore or bead brightness (B) can be determined that equals the product of the absorption cross section (σa) at the excitation wavelength (σa(λex)) and the photoluminescence quantum yield (Φpl). Thereby, an absolute scale based on fundamental and measurable spectroscopic properties can be realized which is independent of particle size, material, and luminophore staining or labeling density and considers the sensitivity of the optical properties of luminophores to their environment. Aiming for establishing such a brightness scale for light-scattering dispersions of luminescent particles with sizes exceeding a few ten nanometers, we demonstrate how the brightness of quasi-monodisperse 25 nm, 100 nm, and 1 µm sized polystyrene particles (PSP), loaded with two different dyes in varying concentrations, can be obtained with a single custom-designed integrating sphere setup that enables the absolute determination of Φpl and transmittance and diffuse reflectance measurements. The resulting Φpl, σa(λex), imaginary parts of the refractive index, and calculated B values of these samples are given in dependence of the number of incorporated dye molecule per particle. Finally, a unitless luminescence efficiency (LE) is defined allowing for the direct comparison of luminescence efficiencies of particles with different sizes. [ABSTRACT FROM AUTHOR]

Glass is the most widely used transparent material for photovoltaic (PV) panels. Unfortunately, the glass introduces an additional interface and therefore optical losses, which can be mitigated using antireflection (AR) coatings. This article reports a scalable method to prepare AR coatings from ZnO nanowires (NWs) sorted by their size. The measured AR performance depends on the coating coverage and ZnO NW size, which is explained by scattering and absorption cross section simulations. Randomly oriented and size fractioned ZnO NWs with an average diameter of 19–30 nm and lengths of 121–273 nm demonstrate increased transmittance and decreased reflectance compared to a glass substrate in case of low coverage. The experimental PV modules with ZnO NW coatings show an 1.2% increase of the short circuit current. A strategy to decouple ZnO NW synthesis from AR coating preparation allows to tune NW reflectance and other optical properties by varying the length, diameter, and orientation of the constituent NWs. The proposed AR coating made from size‐sorted nanomaterials is not limited to ZnO and the method could be adapted to other materials and nanostructures. [ABSTRACT FROM AUTHOR]

Lead-halide perovskite nanocrystals (NCs) have emerged as a novel type of semiconductor nanostructure, attracting great research interests in both fundamental science and practical applications. Here, we compare the optical properties of single CsPbI3 NCs under both one-photon and two-photon excitations, mainly including the photoluminescence (PL) blinking and PL decay dynamics. By means of the PL saturation effect caused by multi-exciton Auger recombination, we have also estimated a two-photon absorption cross section of ∼6.8 × 106 GM for single CsPbI3 NCs. The ability to realize efficient two-photon excitation of single perovskite NCs with strongly suppressed background fluorescence will help not only to promote their bio-imaging and biolabeling applications but also to reveal and manipulate their delicate electronic structures for potential usage in quantum information processing. [ABSTRACT FROM AUTHOR]

A potent AIE-activated 3PM probe with a large three-photon cross-section of action was prepared using molecular engineering, and thus achieving a depth of up to 1895 μm of imaging of the deep structures of the mouse brain after craniotomy. [Display omitted] • A three-photon probe with large η σ 3 is synthesized by elaborately molecular design. • Multiple advantageous principles are incorporated into the molecular design. • The significance of D-A-D strength for three-photon performance is fully verified. • A remarkable depth of 1895 μm for brain structural portrait imaging is realized. • A depth of 1200 μm for hemodynamic imaging is realized. Three-photon microscopy (3PM) utilizing near-infrared-III (NIR-III) excitation has emerged as an effective technology for deep-tissue bioimaging. Within this domain, organic small molecules with aggregation-induced emission (AIE) property prove to be promising candidates as high-quality 3PM imaging agents because of their exceptional optical properties and the general merit of biocompatibility that most organic small molecules possess. However, due to the bidirectional effects of the intrinsic structure distortion of AIE luminogens (AIEgens) on the three-photon absorption cross section (σ 3) and fluorescence quantum yield (η), two crucial factors that determine 3PM performances, the development of high-powered AIE-active 3PM probes with robust η σ 3 remains a formidable challenge. In this work, by synergistically integrating multiple beneficial principles into the molecule design, an innovative AIE-active 3PM probe with a symmetrical quadrupole D–A–D architecture, namely TIT, was successfully constructed. Owing to the harmonized planarity and distortion, as well as strong D–A interaction within TIT, the as-prepared TIT nanoparticles (NPs) exhibited boosted η σ 3 under 1665 nm NIR-III excitation. This breakthrough enabled brain vascular imaging at a remarkable depth of 1895 μm after craniotomy, thus positioning TIT among the top three organic 3PM probes in terms of imaging depth. In addition, successful hemodynamic imaging at a depth of 1200 μm within the mouse brain post-craniotomy was also accomplished. These achievements establish TIT NPs as highly promising probes for in vivo deep-brain three-photon imaging. [ABSTRACT FROM AUTHOR]

The radiative forcing of dust particles in Earth atmosphere is still poorly characterized. A better estimation of the absorption cross section of dust particles in the UV-visible part of the spectrum is thus needed. Among the methods used for this purpose, the Atomic Point Dipole Interaction model has the distinctive advantage of being sensitive to the atomistic geometry of the particle and to the chemical functions it contains. However, this requires an adequate parameterization of the atomic polarizabilities for all the atomic species forming the particle, over the UV-visible spectrum. In this paper, we illustrate how new methodological improvements based on quantum chemistry, allow taking into account the curvature of the carbon network in the parametrization of the carbon atomic polarizabilities, using the C 60 molecule to fit the adequate set of parameters. We thus show how this leads to significant differences in the computed curves of the absorption cross section of pure carbonaceous nanoparticles as a function of the frequency, with respect to calculations performed using parameters issued from graphite. [ABSTRACT FROM AUTHOR]

Silver's inherent optical properties of low absorption cross section, over a broad wavelength range, makes it an attractive material for use in biosensing. We report herein a unique silica template method to synthesize cetrimonium bromide free silver nanorods (AgNRs). The application of AgNRs in metal enhanced fluorescence (MEF) was explored by immobilizing visible/near-infrared (NIR) fluorescent dyes on AgNR assembled substrates exhibiting broadband optical properties. Theoretical modeling was performed to analyze the nanoscale "chaotic nature" of the AgNR substrates, showing that the plasmon band shifts and broadening were attributed to the resonance coupling between assembled nanorods with different conformations. The quantum yield (QY) of NIR dye Alex Fluor 790 was increased dramatically from 4% to 84%, with total fluorescence enhancement up to two orders of magnitudes. In addition, AgNR substrates can also amplify fluorescence emissions from high quantum yield dyes, nearly 10-fold for Alexa Fluor 647 (QY:33%) and threefold for Alexa Fluor 488 (QY:92%). The AgNR demonstrates the capability of dramatically enhancing NIR dye's QY, holding great potential for building up an ultra-sensitive fluorescence bioassay platform for early diagnosis of diseases. [ABSTRACT FROM AUTHOR]

The linear and nonlinear optical properties of two BODIPY derivatives, 1,7-Diphenyl-3,5-bis(9,9-dimethyl-9H-fluoren-2-yl)-boron-diuoride-azadipyrromethene (ZL-61) and 1,7-Diphenyl-3,5-bis(4-(1,2,2-triphenylvinyl)phenyl)-boron-diuoride-azadipyrromethene (ZL-22), were comprehensively investigated based on experimental and theoretical studies. It was found that both compounds show a strong two-photon absorption response in the near-infrared regime, and the two-photon-absorption cross-section values of ZL-61 and ZL-22 were determined to be 8321 GM and 1864 GM at 800 nm, respectively. The improvement of the two-photon absorption cross section in ZL-61 was attributed to the enhancement of the donor group, which was confirmed by transient absorption measurements and DFT calculation. Our results indicate that these BODIPY derivatives are a promising candidate for optical limiting and two-photon imaging applications. [ABSTRACT FROM AUTHOR]

Expressions for the diagonal components of the polarizability tensor, absorption cross sections, and size dependences of the frequencies of the surface plasmon resonance of metal nanodisks are obtained within the classical approximation. The frequency and size dependences of these characteristics are calculated for disks made of different metals and having different aspect ratios. The influence of the aspect ratio on evolution of the frequency dependences of the polarizability tensor components and absorption cross section is analyzed. The most significant factors, affecting splitting of the surface plasmon resonance in metal nanodisks with a low aspect ratio, are determined. [ABSTRACT FROM AUTHOR]

In this work, the electronic, optical and dielectric properties of pure CdO, mixed SnO2/CdO and PVP coated SnO2/CdO nanocomposites were calculated using the finite element method (FEM) and density functional theory. In this approach, the three studied nanostructures are modeled by the following geometric shapes: cubic-CdO, orthorhombic core/shell-SnO2/CdO and nanorod SnO2/CdO/PVP. The electronic structure shows that CdO and SnO2/CdO have semiconductor character. The complex dielectric function, absorption spectra, refractive index, and reflectivity are discussed based on the electronic structure calculations. The obtained results using FEM confirm that the complex permittivity, absorption cross section, reflectivity and complex optical conductivity of CdO nanoparticle depend on their concentration in the surrounding medium and on the nature of the latter. The optical parameters spectra of CdO, SnO2/CdO and CdO/SnO2/PVP have the same evolution in the VU–Vis–NIR band. The effect of PVP coating on the optical properties of CdO/SnO2/PVP nanocomposites is also studied. [ABSTRACT FROM AUTHOR]

Cs2AgBiBr6 double perovskite nanocrystals (NCs) are materials within the halide perovskite family with promising application potential, owing to their nontoxicity and excellent stability. Herein, Cs2AgBiBr6 NCs were synthesized and their photo-physical properties were investigated in detail. The temperature-dependent photoluminescence (PL) test confirms that their PL mechanism is dependent on the competition between the PL originating from carrier recombination in the conduction band and that in the self-trapping states. Their carrier recombination constants (involving the monomolecular, bimolecular, and Auger recombination rate constants) were obtained from transient absorption data and indicated that the monomolecular recombination decreases with the lowering of temperature, while the bimolecular and Auger recombination show opposite trends. The nonlinear optical properties were studied based on the Z-scan technique, with a two-photon absorption cross section of approximately 1906 GM. Our results suggest that Cs2AgBiBr6 NCs can be extensively applied in the field of optoelectronics, and conventional electronic switches will benefit from the excellent carrier dynamics and nonlinear optical properties. [ABSTRACT FROM AUTHOR]

The nominal glasses composition ((40-x) % H3BO3—30% CaO—30% Al2O3—x Dy2O3), where x = 1, 2, 3, 4, 5 and 6) were prepared using the melt quenching technique. The absorption spectra reveal the common normal 13 transition peaks of the Dy2O3-doped glasses. The linear and nonlinear optical properties were calculated. The Photoluminescence spectra and the decay lifetime were examined. The Judd–Ofelt parameters trend was Ω4 > Ω2 > Ω6. The oscillator strength of the experimental, and calculated electronic dipole absorption transition were estimated. The radiative life-time, the radiative branching ratio, the emission and absorption transition cross section were also calculated. The gain coefficient of the transitions was predicted. All the calculated parameters were compared with the previous work. The results reveal that the current glasses composition is a good candidate as a lasing host material and the glasses are highly efficient composition when using in the optical communication fibers. [ABSTRACT FROM AUTHOR]

Extremely elongated, conducting dust particles (also known as metallic 'needles' or 'whiskers') are seen in carbonaceous chondrites and in samples brought back from the Itokawa asteroid. Their formation in protostellar nebulae and subsequent injection into the interstellar medium have been demonstrated, both experimentally and theoretically. Metallic needles have been suggested to explain a wide variety of astrophysical phenomena, ranging from the mid-infrared interstellar extinction at |$\sim \,$| 3–8 |$\, {\rm \mu m}$| to the thermalization of starlight to generate the cosmic microwave background. To validate (or invalidate) these suggestions, an accurate knowledge of the optics (e.g. the amplitude and the wavelength dependence of the absorption cross sections) of metallic needles is crucial. Here we calculate the absorption cross sections of iron needles of various aspect ratios over a wide wavelength range, by exploiting the discrete dipole approximation, the most powerful technique for rigorously calculating the optics of irregular or nonspherical grains. Our calculations support the earlier findings that the antenna theory and the Rayleigh approximation, which are often taken to approximate the optical properties of metallic needles, are indeed inapplicable. [ABSTRACT FROM AUTHOR]

The kinetics for O 2 oxidation of individual graphite and graphene platelet nanoparticles (NPs) were studied as a function of temperature (1200–2200 K) at varying oxygen partial pressures, using a single nanoparticle mass spectrometry method. NP temperature (T NP) was measured by measuring the NP thermal emission spectra during the kinetics studies. The initial oxidation efficiency is found to peak in the 1200–1500 K range, dropping by an order of magnitude as T NP was increased above 2000 K. There were large NP-to-NP variations in the oxidation rates, attributed to variations in the NP surface structure. In addition, the oxidation efficiencies evolved, non-monotonically, as the NPs reacted, decreasing by factors of between 10 and 300. This evolution of reactivity is attributed to changes in the NP surface structure due to the combination of oxidation and annealing. The optical properties, including wavelength dependence of the emissivity and the absorption cross section for the 532 nm heating laser, also tended to evolve as the NPs oxidized, but differently for each individual NP, presumably reflecting differences in the initial structures and their evolution. Image 1 [ABSTRACT FROM AUTHOR]

Time-dependent density functional theory has been used to calculate nonlinear optical (NLO) properties, including the first and second hyperpolarizabilities as well as the two-photon absorption crosssection, for the donor-acceptor molecules p-nitroaniline and dimethylamino nitrostilbene, and for respective materials attached to a gold dimer. The CAMB3LYP, B3LYP, PBE0, and PBE exchangecorrelation functionals all had fair but variable performance when compared to higher-level theory and to experiment. The CAMB3LYP functional had the best performance on these compounds of the functionals tested. However, our comprehensive analysis has shown that quantitative prediction of hyperpolarizabilities is still a challenge, hampered by inadequate functionals, basis sets, and solvation models, requiring further experimental characterization. Attachment of the Au2S group to molecules already known for their relatively large NLO properties was found to further enhance the response. While our calculations show a modest enhancement for the first hyperpolarizability, the enhancement of the second hyperpolarizability is predicted to be more than an order of magnitude. [ABSTRACT FROM AUTHOR]

Accurate measurements of the horizontal and vertical distribution of atmospheric aerosol particle optical properties are key for a better understanding of their impact on the climate. Here we present the results of a measurement campaign based on instrumented flights over north-eastern Spain. We measured vertical profiles of size-segregated atmospheric particulate matter (PM) mass concentrations and multi-wavelength scattering and absorption coefficients in the western Mediterranean basin (WMB). The campaign took place during typical summer conditions, characterized by the development of a vertical multi-layer structure, under both summer regional pollution episodes (REGs) and Saharan dust events (SDEs). REG patterns in the region form under high insolation and scarce precipitation in summer, favouring layering of highly aged fine-PM strata in the lower few kma.s.l. The REG scenario prevailed during the entire measurement campaign. Additionally, African dust outbreaks and plumes from northern African wildfires influenced the study area. The vertical profiles of climate-relevant intensive optical parameters such as single-scattering albedo (SSA); the asymmetry parameter (g); scattering, absorption and SSA Ångström exponents (SAE, AAE and SSAAE); and PM mass scattering and absorption cross sections (MSC and MAC) were derived from the measurements. Moreover, we compared the aircraft measurements with those performed at two GAW–ACTRIS (Global Atmosphere Watch–Aerosol, Clouds and Trace Gases) surface measurement stations located in north-eastern Spain, namely Montseny (MSY; regional background) and Montsec d'Ares (MSA; remote site). Airborne in situ measurements and ceilometer ground-based remote measurements identified aerosol air masses at altitudes up to more than 3.5 kma.s.l. The vertical profiles of the optical properties markedly changed according to the prevailing atmospheric scenarios. During SDE the SAE was low along the profiles, reaching values < 1.0 in the dust layers. Correspondingly, SSAAE was negative, and AAE reached values up to 2.0–2.5, as a consequence of the UV absorption increased by the presence of the coarse dust particles. During REG, the SAE increased to > 2.0, and the asymmetry parameter g was rather low (0.5–0.6) due to the prevalence of fine PM, which was characterized by an AAE close to 1.0, suggesting a fossil fuel combustion origin. During REG, some of the layers featured larger AAE (> 1.5), relatively low SSA at 525 nm (< 0.85) and high MSC (> 9 m2g-1) and were associated with the influence of PM from wildfires. Overall, the SSA and MSC near the ground ranged around 0.85 and 3 m2g-1 , respectively, and increased at higher altitudes, reaching values above 0.95 and up to 9 m2g-1. The PM, MSC and MAC were on average larger during REG compared to SDE due to the larger scattering and absorption efficiency of fine PM compared with dust. The SSA and MSC had quite similar vertical profiles and often both increased with height indicating the progressive shift toward PM with a larger scattering efficiency with altitude. This study contributes to our understanding of regional-aerosol vertical distribution and optical properties in the WMB, and the results will be useful for improving future climate projections and remote sensing or satellite retrieval algorithms. [ABSTRACT FROM AUTHOR]

Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs), exhibiting excellent optical properties such as long photoluminescence lifetime, narrow emission bandwidth, and low autofluorescence background, have been applied in many fields, especially in biological analysis and medical diagnostics. Despite the exciting progress, the applications of Ln3+-doped UCNPs are hindered by the small absorption cross-section and low upconversion luminescence efficiency of Ln3+. To this regard, several effective strategies associated with energy transfer designing have been proposed to modulate the upconversion luminescence properties of Ln3+ in the past few decades. In this feature article, we focus on the most recent development of optical property designing in Ln3+-doped UCNPs on the basis of energy transfer between Ln3+–Ln3+, Ln3+–dyes, and Ln3+–quantum dots. Some future efforts towards the energy transfer designing in Ln3+-doped UCNPs are also proposed. [ABSTRACT FROM AUTHOR]

A series of novel monodisperse, structurally well defined vinylene‐linked phenothiazine oligomers containing up to 7 phenothiazine units have been designed and synthesized by Heck reaction and McMurry reaction with a convergent approach. These conjugated oligomers showed a progressive bathochromic shift of the absorption maxima and high fluorescence quantum yields in solutions. Notably, the oligomers without strong donor and acceptor units exhibit two‐photon absorption properties, and the two‐photon absorption cross sections (δ) increase with the number of covalently linked phenothiazine units, and δ reaches up to 2071 GM for the one with 7 phenothiazine units at 800 nm. The oligomers might be used as models to study structure–property relationship for their corresponding polymers or applied in organic electronic materials. [ABSTRACT FROM AUTHOR]

Nonlinear absorption of suspensions of graphene nanosheets with the number of layers from one to three was studied using the Z-scan method with femtosecond excitation at 1030 nm wavelength. A large modulation depth and lower saturation intensity of the suspensions as compared with nonlinear absorption of single-layer graphene were shown. Dynamics of photoexcited carriers for different duration of excitation pulse was considered. The values of the absorption cross section and the density of photoexcited carriers in single-layer graphene were estimated. The presence of two-photon absorption (TPA) in suspensions of graphene nanosheets and the absence of noticeable TPA in single-layer graphene were shown. [ABSTRACT FROM AUTHOR]

Unlike conventional type-I InP-based quantum dots (QDs), inverted type-I QDs can push the emission wavelength to the near-infrared (NIR) range. However, the fundamental optical properties of such kinds of QDs have yet to be studied in depth. In this work, we report the optical properties of inverted type-I ZnSe/InP/ZnS QDs with photoluminescence (PL) emission in the first biological window. Using femtosecond ultrafast transient absorption, the electron-injection time, Auger lifetime, and hot-carrier cooling time of the inverted type-I QDs are determined. Their temperature-dependent PL spectrum reveals that these QDs possess a higher exciton-binding energy and weaker carrier-phonon coupling effect than conventional type-I InP-based QDs. Interestingly, the QDs have strong two-photon absorption cross sections in the second biological window, up to 5120 GM at 1200 nm. These results suggest that ZnSe/InP/ZnS QDs have potential applications for light emitting devices and deep-tissue bioimaging. • The electron-injection time, Auger lifetime, and hot-carrier cooling time of the inverted type-I ZnSe/InP/ZnS quantum dots with near infrared emission were determined. • The exciton-binding energy, coefficient of the bandgap change and carrier-phonon coupling strength of the quantum dots were investigated. • The two-photon absorption cross sections of the quantum dots in the second biological window were determined. [ABSTRACT FROM AUTHOR]

[Display omitted] • Er3+ doped bismuth flourophosphate glasses were successfully prepared by high temperature melting method. • The influence of modifier cations as ligand field surrounding Er3+ ions on the optical properties was analyzed. • The visible and near-infrared emission of Er3+ doped bismuth flourophopsphate glasses were investigated. • Broadband emissions at visible and near-infrared were observed with the excitation of 379 nm and 980 nm respectively. • Various luminescence properties determined and compared with different compositional incorporation. Bismuth flourophosphate glasses doped with Er3+ ions (0.5 mol %) were synthesized using different modifier fluorides with the aid of melt quenching route. The glass samples were labelled as PBiBa AF T (where AF = Li, Na, Mg, K, Ca and Sr fluorides). The influence of cations of network modifiers on the structure and thereby spectroscopic properties of Er3+ ions was analysed via Powder XRD, FTIR, optical absorption and photoluminescence. Existence of relevant vibrational groups and modifications in structure due to the different admixture modifier cations were recognized via FTIR spectra. The Judd-Ofelt parameters abide by the trend Ω 2 > Ω 6 > Ω 4 in the PBiBa Li T, PBiBa K T, PBiBa Ca Tand PBiBa Sr T glasses whereas the trend was noticed to be Ω 2 > Ω 4 > Ω 6 for PBBi Na T and PBiBa Mg T glasses respectively. The visible emission spectra were recorded by exciting at 379 nm exhibit three emission bands centered at 526 nm, 544 nm and 686 nm. NIR emission spectra were recorded by exciting at 980 nm exhibit broad emission at 1535 nm. Admixture of different cations could exhibit change in luminescence intensity and radiative parameters of the prepared glasses. Spectroscopic parameters such as radiative transition probability (A), branching ratio (β), absorption cross section (∑), effective bandwidth (Δλ eff) and optical band gain (σ e × Δλ eff) are calculated. The mid infrared spectroscopic features were investigated. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is known to have major impacts on both climate and human health and is therefore of global importance, particularly in regions close to large populations that have strong sources. The size-resolved mixing state of BC-containing particles was characterised using a single-particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain (IGP) during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons of 2016. Over the IGP, BC mass concentrations were greater (1.95 µgm-3) compared to north-west India (1.50 µgm-3) and north-east India (0.70 µgm-3) during the pre-monsoon season. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter <0.16 µm and coating thickness <50 nm) and a mode of moderately coated BC (core diameter <0.22 µm and coating thickness of 50–200 nm). The IGP and north-east India locations exhibited moderately coated black carbon particles with enhanced coating thicknesses, core sizes, mass absorption cross sections, and scattering enhancement values compared to much lower values present in the north-west. The coating thickness and mass absorption cross section increased with altitude (13 %) compared to those in the boundary layer. As the monsoon arrived across the region, mass concentration of BC decreased over the central IGP and north-east locations (38 % and 28 % respectively), whereas for the north-west location BC properties remained relatively consistent. Post-monsoon onset, the coating thickness, core size, mass absorption cross section, and scattering enhancement values were all greatest over the central IGP much like the pre-monsoon season but were considerably reduced over both north-east and north-west India. Increases in mass absorption cross section through the atmospheric column were still present during the monsoon for the north-west and central IGP locations, but less so over the north-east due to lack of long-range transport aerosol aloft. Across the Indo-Gangetic Plain and north-east India during the pre-monsoon and monsoon seasons, solid-fuel (wood burning) emissions form the greatest proportion of BC with moderately coated particles. However, as the monsoon develops in the north-east there was a switch to small uncoated BC particles indicative of traffic emissions, but the solid-fuel emissions remained in the IGP into the monsoon. For both seasons in the north-west, traffic emissions form the greatest proportion of BC particles. Our findings will prove important for greater understanding of the BC physical and optical properties, with important consequences for the atmospheric radiative forcing of BC-containing particles. The findings will also help constrain the regional aerosol models for a variety of applications such as space-based remote sensing, chemistry transport modelling, air quality, and BC source and emission inventories. [ABSTRACT FROM AUTHOR]

Fluorotellurite glasses tri-doped with Tm3+, Er3+ and Bi ions were investigated. The measured parameter ΔT (116 °C) confirmed that the prepared glasses had good stability. An ultra-broadband fluorescence emission (950–1670 nm) was observed with a full-width at half-maximum (FWHM) of 560 nm, which covered the entire bands of O, E, S, C, L and U. The 1800 nm fluorescence intensity of Tm3+/Er3+ co-doped and Tm3+/Er3+/Bi tri-doped glasses was enhanced compared to Tm3+ doped glass, which indicates that there is energy transfer between Tm3+, Er3+ and Bi ions. The maximum fluorescence lifetime of the prepared glasses was 7.39 ms, indicating the excellent fluorescence performance at 1800 nm. Additionally, the maximum absorption cross section (σ abs = 1.77 × 10−20 cm−2) and emission cross section (σ em = 7.61 × 10−20 cm−2) suggest that the Tm3+/Er3+/Bi tri-doped glasses have good optical absorption properties and high gain fluorescence emission. The above results indicate that the Tm3+/Er3+/Bi tri-doped fluorotellurite glasses have good application prospects in the field of fiber amplifiers and near-infrared lasers. [ABSTRACT FROM AUTHOR]

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(Gd 0.5 Lu 0.5)F 4 :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. Unlabelled Image • Nd3+ doped NaGd 0.5 Lu 0.5 F 4 nanoparticles of average size 55 nm were successfully synthesized. • Nanoparticles show near infrared emission, magnetic and X-ray absorption features. • Nanoparticles show good contrast under CT, MRI and optical imaging. • Near infrared optical penetration depth of up to 8 mm was observed in tissues. • Cell viability experiments confirm that the nanoparticles are non-toxic. [ABSTRACT FROM AUTHOR]

A set of linear and asymmetric coumarin–imidazole hybrid compounds having a N,N‐diethylamine at 7‐position and imidazole at 3‐position on the coumarin were synthesized. Insertion of thiophene π‐spacer between coumarin and imidazole moieties (5b, 5d) leads to redshifted absorption and emission compared to 5a and 5c. All the compounds show a noticeable response to trifluoroacetic acid with a redshifted absorption and an increase in emission intensity by twofold. The ratio of ground and excited state acidity constant was calculated using Förster energy cycle, and the ratios were found to be 0.25, 0.96, 0.52 and 1.87, respectively, for 5a‐5d. Due to the thiophene π‐spacer, elongation of π‐conjugation in 5b and 5d leads to high values of polarizability (α), first‐order hyperpolarizability (β) and second‐order hyperpolarizability (γ). Compound 5b exhibits a high value (895 GM) of two‐photon absorption cross section (σ2PA), measured using two‐level model. [ABSTRACT FROM AUTHOR]

Abstract Nonlinear optical properties of colloidal CdSe quantum dots conjugated with proteins were investigated in a wide spectral range with the two-photon excited emission technique using a tunable femtosecond laser system in the range from 700 to 1000 nm. The most significant value of the two-photon absorption cross section σ 2 for 2.9 nm size hydrophilic CdSe quantum dot was equal to 4 505 GM, while the two-photon excitation action cross section σ 2 ·QY was found to be 0.101 GM at 900 nm. The nonlinear absorption properties are present as appropriate cross sections normalized per molecular weight which allows comparison of the nonlinear properties of the studied quantum dots with various nanosystems or organic dyes. The properties of these proteins covering hydrophilic colloidal quantum dots can be potentially useful for nonlinear bioimaging. Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

The transmission of intrinsic, antimony-doped, and gallium-doped Ge single crystals in the THz spectral range have been experimentally investigated. It is shown that the attenuation coefficient of intrinsic germanium in the range of 160‒220 μm is at a level of ~0.5 cm‒1, a value comparable with that for silicon. The free-carrier absorption cross sections of silicon and germanium are significantly different, which may be caused by the difference in the mechanisms of carrier–phonon interaction in these materials. [ABSTRACT FROM AUTHOR]

Abstract Nonlinear optical and limiting properties of nickel, cobalt metal-organic complexes and ligand (L) {L = N,N′-o-phenylenebis (4-hyrdoxy-salicylideneimine)} were studied using Z-scan technique using Q-switched Nd: YAG laser with nanosecond pulses at 532 nm. The results reveal that metal complexes exhibit large negative nonlinear refractive index (n 2) of the order of 10−11 esu. The metal complexes displays large nonlinearity than the ligand due to effective charge delocalization between metal ion and ligand. The magnitude of ground state absorption cross section is small compared to the effective excited-state absorption cross section implying the observed nonlinearity is due to reverse saturable absorption. Further, metal-organic complexes exhibit enhanced optical limiting behaviour at nanosecond laser pulses. Graphical abstract Image 1 Highlights • Novel materials exhibiting strong nonlinear optical properties. • The inclusion of the metal ion enhances the photostability and optical nonlinearity of the molecule. • Third-order nonlinear optical susceptibility is of the order of 10−13 esu. • Investigated samples are good candidates for optical power limiting. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosol is the strongest sunlight-absorbing aerosol, and its optical properties are fundamental to radiative forcing estimations and retrievals of its size and concentration. BC particles exist as aggregate structures with small monomers and are widely represented by the idealized fractal aggregate model. In reality, BC particles possess complex and nonideal minor structures besides the overall aggregate structure, altering their optical properties in unforeseen ways. This study introduces the parameter "volume variation" to quantify and unify different minor structures and develops an empirical relationship to account for their effects on BC optical properties from those of ideal aggregates. Minor structures considered are as follows: the polydispersity of monomer size, the irregularity and coating of the individual monomer, and necking and overlapping among monomers. The discrete dipole approximation is used to calculate the optical properties of aggregates with these minor structures. Minor structures result in scattering cross-section enhancement slightly more than that of absorption cross section, and their effects on the angle-dependent phase matrix as well as asymmetry factor are negligible. As expected, the effects become weaker with the increase in wavelength. Our results suggest that a correction ratio of 1.05 is necessary to account for the mass or volume normalized absorption and scattering of nonideal aggregates in comparison to ideal ones, which also applies to aggregates with multiple minor structures. In other words, the effects of minor structures are mainly contributed by their influence on particle volume/mass that cannot be ignored, and a relative difference of approximately 5 % is noticed after removing the volume effects. Thus, accurate knowledge and evaluation of BC volume/mass are more important than those of the minor structures themselves. Most importantly, the simulations of optical properties of nonideal aggregates are greatly simplified by applying the empirical relationship because they can be directly obtained from those of the corresponding ideal aggregates, a volume/mass difference parameter, and the correction factor, i.e., 1.05, not the detailed minor structure information. We expect this convenient treatment to find wide applications for the accounting for the effects of nonideal minor structures on BC optical properties. [ABSTRACT FROM AUTHOR]

Optical transition and near-infrared upconversion luminescence properties of Er3+ single-doped and Er3+, Yb3+ co-doped YNbO 4 phosphors are reported. Based on the framework of Judd-Ofelt theory and modified Judd-Ofelt calculation method, the optical transition properties of Er3+ and Yb3+ ions in YNbO 4 : Er3+, Yb3+ sample were studied, respectively. The calculated results showed that the absorption cross-section of Er3+ ion at ∼1550 nm is larger than that at ∼980 nm in YNbO 4 : Er3+ phosphor. And, the absorption cross-section of 2F 7/2 → 2F 5/2 transition of Yb3+ in YNbO 4 : 15.0 mol% Er3+, 15.0 mol% Yb3+ sample was calculated to be 138.70 × 10−20 cm2. According to the emission cross section of Er3+ (4I 11/2 → 4I 15/2) and the absorption cross section of Yb3+ (2F 7/2 → 2F 5/2), the energy transfer rates from Er3+ to Yb3+ were quantitatively analyzed via the Föster-Dexter model. Furthermore, 1550 nm was selected as the excitation wavelength, the near-infrared upconversion emission spectra of YNbO 4 : Er3+, Yb3+ samples were measured. It was found that the sample has strong emission at ∼980 nm and the emission intensity was still enhanced with the incorporation of Yb3+. • YNbO 4 : Er3+, Yb3+ phosphors were synthesized via a solid-state reaction method. • The absorption cross section of Yb3+ in YNbO 4 phosphor was confirmed. • The energy transfer rates from Er3+ to Yb3+ in YNbO 4 phosphors were calculated. • The YNbO 4 : Er3+, Yb3+ sample has strong ∼980 nm emission excited by 1550 nm. [ABSTRACT FROM AUTHOR]

In this paper, Φ50 × 50 mm Nd, Ho: NaY 0.1 Gd 0.89 (WO 4) 2 crystals have been successfully grown by Czochralski. The crystal structure, doping concentration, thermal properties, fluorescence spectrum, emission cross section, fluorescence lifetime and energy transfer mechanism of Nd, Ho: NaY 0.1 Gd 0.89 (WO 4) 2 crystals have been systematically studied. The results show that the covalent bond effect of W–O bond makes NaY 0.1 Gd 0.89 (WO 4) 2 crystal have high doping ability. Low thermal expansion coefficient and excellent thermal conductivity reduce the possibility of dislocation defects. Under the excitation of 808 nm light source, a wide emission band at 2 μm is obtained. The absorption cross section, emission cross section and gain coefficient are obtained by absorption spectrum calculation. It shows that the incorporation of Y3+ ions can improve the luminous efficiency, widen the spectral line width and adjust the emission spectrum width. The low output pump threshold, high level lifetime and large absorption cross section of laser show great potential for high power laser systems. • The Nd,Ho:NaY0.1Gd0.89(WO4)2 crystal was successfully grown by Czochralski method with the size of Φ50x50mm. • The covalent bonding effect of W-O bonding gives NaY0.1Gd0.89(WO4)2 crystals a high doping ability. • The doping of Y3+ ions can improve the luminescence efficiency, broaden the optical spectral line width and regulate the emission spectrum width. [ABSTRACT FROM AUTHOR]

The aqueous–phase reaction of carbonyls with reduced nitrogen compounds (RNCs) is considered an important pathway for the formation of secondary BrC, and these particles could greatly impact the global climate. However, our knowledge of their properties is still limited. In this study, we measured the optical properties, cloud condensation nuclei (CCN) activity (represented as hygroscopicity parameter κ CCN), and effective density (ρ eff) under varied reaction conditions for BrC mixtures formed by reactions between two α–dicarbonyls (glyoxal GX and methylglyoxal MG) and three RNCs (ammonium sulfate AS, glycine GC, and dimethylamine DA). Our results showed a wide range of particle ρ eff from 1.08 to 1.66 g cm−3, depending on the type of RNCs reactant. At 532 nm wavelength, the real part n of complex refractive index ranged from 1.41 to 1.60 and the imaginary part k of BrC ranged from 0.024 to 0.043, and the absorption cross section for MG mixtures were 20.3–51.0% higher than those of GX mixtures. These values did not appear to vary significantly with mixing molar ratios between RNCs and α–dicarbonyls (10:1, 1:1, and 1:3) for mixtures with the same reactants, but the mass absorption cross section for mixtures after a reaction time of 14 days were 1.57–74.2% higher than those of mixtures after reaction times of 0.5 and 7 days. The κ CCN values of different BrC were consistent with the order of κ CCN for single RNCs, i.e., AS–containing (0.349–0.428) > GC–containing (0.221–0.352) > DA–containing (0.090–0.131), and showed an overall increasing trend (1.47–59.3%) with the RNCs content. Our results highlight the importance of reaction conditions on secondary BrC properties and are helpful for a more accurate assessment of aerosol radiative forcing. [Display omitted] • Absorptivity of secondary brown carbon was enhanced after days of dark reactions. • Particle density depended on reduced nitrogen compound reactants. • The reduced nitrogen compound content determined the hygroscopicity of brown carbon. • ZSR model predicted CCN activity of GC mixture well but not for AS and DA mixtures. [ABSTRACT FROM AUTHOR]

The interaction of a cell with light is described by electromagnetic theory through parameters such as absorption cross-section, scattering cross-section and scattering phase function, which are essential radiative properties in radiative transfer theory for analysis of light transport in dispersed media. The radiative properties of microalgae vary with time due to the growth process of cell division and metabolism. In this paper, the growth-dependent radiative properties of Spirulina platensis (a microalgae with filamentous helix structure) was experimentally investigated in batch cultivation. The microalgae was cultivated in a flat-plate photobioreactor under dark and light cycle 12 h and 12 h with irradiance of 2000–2500 lx. The absorption and scattering cross-sections of Spirulina platensis were measured in the spectral region 380–850 nm at different growth time. The experimental results showed temporal scaling behavior of the radiative properties of this filamentous microalgae, which confirms the temporal scaling law of radiative properties of microalgae reported recently, namely, the temporal scaling function (TSF) defined as the ratio of spectral absorption or scattering cross-sections at different growth time to that at stationary phase is nearly wavelength independent. This paper is the first work on the temporal scaling behavior of radiative properties of Spirulina platensis , and also provides additional experimental evidence on the general validity of the temporal scaling law of radiative properties of microalgae cells. [ABSTRACT FROM AUTHOR]

Pyrene molecule, with excellent photophysical properties (strong absorption cross section, excellent emission properties and a long-excited state lifetime), excellent thermal and photochemical stability, has been widely used as a building block for the synthesis of pyrene-based fluorophores for optoelectronic applications. In this work, we report the synthesis of two series of pyrene–π–A compounds, series I (3–6) and II (10–13), in which nitro, cyano, cyanoacrylonitrile and cyanoacrylic acid as electron acceptor groups are connected to the pyrene core via aryl or fluoroaryl π-conjugating bridges. The incorporation of fluorine atom on the π-extension bridge cause a slightly red-shift at emission wavelength (λ em) in solution and polymethylmethacrylate (PMMA) films and increase the Stokes shift due to greater stabilization of molecular orbitals in the excited state, especially for series I. Solvatochromic measurements and theoretical computational studies suggest a higher intramolecular charge transfer in the excited state for series II when compared to series I due to their stronger electron acceptor moieties. All pyrene derivatives are stable and exhibited initial mass loss at temperature above 200 °C. The good photophysical and thermal properties of the synthesized pyrene derivatives, associated with high molar absorption coefficients in the UV spectrum and good fluorescence emission in the range of 430–480 nm (series I) and 505–567 nm (series II) in PMMA films, make them possible candidates for organic light-emitting diode (OLED) and luminescent down-shifting (LDS) layers for stable perovskite solar cells, respectively. [Display omitted] • Two series of pyrene–π–A compounds with different acceptor groups were reported. • The acceptor groups are connected to the pyrene core via phenyl or fluoroaryl bridges. • Optical/electrochemical properties were investigated by experimental and theoretical studies. • Pyrene derivatives showed ICT mechanism between donor and acceptor moieties. • Series I and II showed good properties to be used in OLED and LDS layer for stable perovskite solar cells, respectively. [ABSTRACT FROM AUTHOR]

The 1 at.% Er:CaF 2 transparent ceramics were prepared by the air pre-sintering and hot isostatic pressing (HIP) using nano-powders synthesized by the co-precipitation method. The influence of pre-sintering temperature and HIP post-treatment on the density, microstructures, optical and photoluminescence properties of Er:CaF 2 ceramics were investigated. After HIP post-treatment (650 °C × 2 h, 100 MPa Ar), the pores in the pre-sintering ceramics were gradually eliminated and high transparency was achieved. The maximum in-line transmittance of the HIPed 1 at.% Er:CaF 2 reaches 90.5% at 1600 nm (2.8 mm thickness) when the pre-sintered temperature is 625 °C.The absorption cross section was calculated. The strong absorption peak at 1530 nm reveals an unfavorable infrared emission. The main emission peak at 1530 nm, which is derived from the 4I 13/2 → 4I 15/2 transition of Er3+, can be observed under excitation of 980 nm. Owing to the long lifetime of 4I 13/2 (32.3 ms) and large emission cross section, the 1 at.% Er:CaF 2 transparent ceramics have great potential to achieve a good NIR laser performance in the 1.5 μm region. • Er:CaF 2 transparent ceramics were prepared by air pre-sintering and HIP post-treatment. • Fine-grain Er:CaF 2 transparent ceramics with uniform distribution were obtained. • Er:CaF 2 transparent ceramics showed high in-line transmittance of 90.5% at 1600 nm. [ABSTRACT FROM AUTHOR]

A series of 75TeO2-(20-x)Li 2 O-xBaO glasses was successfully synthesized using the melt-quenching method. The glass samples were labeled as TLB05, TLB10, TLB15, TLB20 and TLB25 for x = 5, 10, 15, 20 and 25 mol% respectively. The prepared glasses were studied for their structural, optical, and radiation shielding properties. The optical band gap of the glasses decreased linearly from 3.45 to 3.28 eV with BaO in the range 5−25 mol%. The analysis of the thermal properties shows an increase in T g values with the replacement of Li 2 O by BaO. The gamma ray shielding coefficients for the glasses estimated by FLUKA simulation and validated by XCOM varied from 0.0329 to 1.4383 cm2g−1, 0.0332 – 1.4879 cm2g−1, 0.0334 – 1.5327 cm2g−1, 0.0335 – 1.5671 cm2g−1, and 0.0336 – 1.5964 cm2g−1 for BaO concentration of 5%, 10%, 15%, 20%, and 25% respectively. Generally, the introduction of BaO improved the photon and charged particles (electron, proton, alpha particle, carbon ions) absorbing parameters of the glasses. The fast neutron removal cross section of the TLB glasses grew from 0.0995 to 0.1014 cm−1 as the molar concentration of BaO declines from 25 to 5 mol%. The increase in the BaO content also quenched the thermal neutron absorption cross section. For TLB5 – TLB25, the coherent, incoherent, absorption, and total thermal neutron cross sections varied between 1.0582 and 1.2059 cm−1, 0.1251 – 0.0024 cm−1, 9.5411 – 0.0876 cm−1, and 10.7244 – 1.2958 cm−1 accordingly. In general, TLB25 displayed the most effective photon shielding ability but the weakest neutron absorber. The TLB glasses in addition showed superior radiation shielding ability compared to some conventional shields. [ABSTRACT FROM AUTHOR]

[Display omitted] • Narrowing of the half-width of the fluorescence band as compared to the half-width of the absorption band. • Large Stokes shift which is solvent dependent. • Fast response of the dyes to changes in pH. • Tribranched chromophore exhibit a large σ 2 eff value. • Formation of the inclusion complexes with β-CD, which results in enhanced fluorescence. A common motif in the design of organic dye compounds is that of an electron donor and an acceptor moiety linked through a conjugated bridge, but more complicated structures can also be built using such motifs as building blocks. Following these principles, we synthesized two styrylpyridinium dyes, a linear one and a branched molecule composed of three units of the mono moiety connected by benzyl group and investigated their photophysical properties in different environments: their linear absorption, one-photon excited fluorescence and two-photon absorption properties. The compound with the symmetrically substituted phenyl core shows a redshift of the absorption and fluorescence bands. Spectrally resolved two-photon absorption cross section measurements carried out by femtosecond Z-scan technique show that the value for the trimer is over twelve times larger than that for the monomer, and not just three times as expected from the molar mass increase. Large two-photon absorption (2PA) values were measured in the near infrared (NIR) region. The prototropic study indicates that the protonation of the amino group blocks a lone pair on the nitrogen atom, making the photoinduced electron transfer process from the amine group to the pyridinium ring ineffective. This results in the reduction of the long-wavelength absorption with a simultaneous increase of the band in the short-wavelength region of the spectrum and a decrease in the fluorescence intensity. The behavior of dyes in the presence of β-cyclodextrin was also studied based on NMR, UV–Vis, and fluorescence spectroscopy. The performed experiments indicated the formation of 1:1 inclusion complex in aqueous solution. [ABSTRACT FROM AUTHOR]

By changing or fine-tuning the surface structure of the metal, the characteristics of surface plasmon – especially the interaction with light – can be customized. In this work, we numerically design a plasmonic nanostructure composed of a pair of symmetrical bifurcation nanostructures. An underlying optical property of the observed scattering and absorption cross section spectra and physical mechanism is illustrated by analyzing spatial distributions of the magnetic field, electric field, and surface current component at resonant wavelengths. Moreover, the extremely intense and highly confined electromagnetic fields induced in the bifurcation plasmonic nanostructure provide a sensitive environment to probe minor changes in the dielectric environment. Such high-performance composite nanostructure provides great potential for the application of sensing. • For this composite nanostructure, we focus on the optical properties of bifurcated nanostructure as shown in Fig. 2 (this paper). Especially in Fig. 2 (b) and (c), we can see the optical properties of single nanorod tetramer and fork dimer. It is clearly observed that the scattering spectrum of the bifurcation nanostructure is split into two resonance peaks by comparing with single nanorod tetramer or fork dimer, and a groove is formed in the middle with a sharp dip in scattering intensity and the corresponding absorption spectrum is significantly enhanced. The extremely intense and highly confined electromagnetic fields induced in the bifurcation plasmon nanostructure provides a sensitive environment to probe minor changes in the dielectric environment. • In this article, the structure we designed has both excellent sensing performance and field enhancement performance which can be used to design multi-function chips. • Our design is a simple flat structure, which is easy to process and manufacture in actual production. [ABSTRACT FROM AUTHOR]

• Optical properties are computed for fractal-like aggregate black carbon (BC) aerosols coated with different substances. Two models are used for these aerosols: (i) the coated aggregate model (model I), where coating is added to the voids and surroundings of BC fractal-like aggregates, and (ii) the closed-cell aggregate model (model II), where coating is added concentrically to each monomer of BC fractal-like aggregates. Our results favor choosing the coated aggregate model (model I) to simulate scattering and absorption by coated BC aerosols because this model is morphologically more realistic, and because this model yields mass absorption cross section (MAC) and backscattering linear depolarization ratio (LDR) values that are consistent with field measurements. Moreover the corresponding computed degree of linear polarization (DoLP) and LDR values are very sensitive to changes in the coating volume fraction (fvol) and the coating refractive index (m). With the same absorbing BC core, the MAC value increases steadily with increasing fvol and m values. For example, using a density of 1.8 g/cm3 and BC refractive index 1.95 + i0.79, the calculated MAC values for uncoated BC aggregates range from 6.2 to 6.8 m2/g at 0.55 µm. When coating material is applied to the BC aggregates, the calculated MAC values for model i particles increase to between 9.8 and 13.2 m2/g (depending on m) when fvol = 87.5%. The backscattering LDR values also tend to increase with the increasing m values for the shapes and sizes considered in our study. For model i particles, the backscattering LDR values span a wide range of 4.2% to 27.8% at a wavelength of 0.35 µm at fvol = 87.5% when m increases from 1.33 to 1.55. Our results are relevant to analyses of polarimetric and lidar observations of smoke particles, especially when these particles undergo hygroscopic growth. Optical properties are computed for fractal-like aggregate black carbon (BC) aerosols coated with different substances. Two models are used for these aerosols: (i) the coated aggregate model (model I), where coating is added to the voids and surroundings of BC fractal-like aggregates; and (ii) the closed-cell aggregate model (model II), where coating is added concentrically to each monomer of BC fractal-like aggregates. Our results favor choosing the coated aggregate model (model I) to simulate scattering and absorption by coated BC aerosols because this model is morphologically more realistic, and because this model yields mass absorption cross section (MAC) and backscattering linear depolarization ratio (LDR) values that are consistent with field measurements. Moreover the corresponding computed degree of linear polarization (DoLP) and LDR values are very sensitive to changes in the coating volume fraction (fvol) and the coating refractive index (m). With the same absorbing BC core, the MAC value increases steadily with increasing fvol and m values. For example, using a density of 1.8 g/cm3 and BC refractive index 1.95 + i0.79, the calculated MAC values for uncoated BC aggregates range from 6.2 to 6.8 m2/g at 0.55 µm. When coating material is applied to the BC aggregates, the calculated MAC values for model I particles increase to between 9.8 and 13.2 m2/g (depending on m) when fvol = 87.5%. The backscattering LDR values also tend to increase with the increasing m values for the shapes and sizes considered in our study. For model I particles, the backscattering LDR values span a wide range of 4.2–27.8% at a wavelength of 0.35 µm at fvol = 87.5% when m increases from 1.33 to 1.55. Our results are relevant to analyses of polarimetric and lidar observations of smoke particles, especially when these particles undergo hygroscopic growth. [ABSTRACT FROM AUTHOR]

Abstract: Complex refractive index for submicron absorbing spheres was determined by simultaneously measuring absorption coefficients and number concentrations with a multiangle absorption photometer and a condensation particle counter, respectively. The absorption cross section calculated from the absorption coefficient and the number concentration was fitted to the absorption cross section calculated using Mie theory. For homogeneously dyed spheres, the absorption cross section depended on the size of sphere. For non-homogeneously dyed spheres, however, the absorption cross section had nothing to do with the size of sphere. It is concluded that the ability to measure refractive index by our method held good as long as the absorption phenomenon takes place in the near field surrounding particles surface. To the best of our knowledge, it is for the first time that the refractive index was determined by only absorption measurements and theory. This method is believed to help understand the fundamental of the optical properties for other absorbing particles. [Copyright &y& Elsevier]

An understanding of soot aggregate optical properties is needed for the interpretation of optical measurements of soot. A modified cluster-cluster aggregation (MCCA) was used to numerically gen-erate fractal aggregates containing 15-600 primary particles of dp = 30 nm diameter. For each size, the aggregates with fractal dimension Df = 1.78 and 2.1 (with kf = 2.24 and 2.26, respectively) were selected, and the scattering and absorption cross sections were calculated using the discrete dipole approximation (DDA). For un-coated aggregates, the optical properties of these numerically gen-erated aggregates were compared with the Rayleigh-Debye-Gans (RDG) approximation. It was found that the differences in the op-tical cross sections obtained from the two methods were small. In addition, it was also found that the aggregates with similar frac-tal dimension and fractal prefactor exhibit small variations in the absorption and scattering cross sections. For aggregates with trans-parent coatings, DDA predicted larger absorption than the core-shell Mie model for volume-equivalent spherical particles. The coating-induced absorption enhancement increases with coating thickness from 10% for a 5-nm layer to about 50%-75% absorp-tion enhancement for a coating thickness of 20 nm. The presence of the coating on the aggregates also results in an increase in the discrepancy between the scattering predicted by the DDSCAT and the equivalent core-shell Mie model with the scattering discrepan-cies become larger as the coating thickness increases (the scattering discrepancies increases from 65% to 75% and from 20% to 25% for aggregates with N = 200 and 15, respectively). [ABSTRACT FROM AUTHOR]

Abstract: In this work, aza-boron-dipyrromethene (aza-BODIPY) compounds containing methoxy and hydroxy groups were synthesized. The effects of substitution and intramolecular charge transfer on linear and nonlinear optical absorptions (especially two photon absorption) of these BODIPY derivatives were investigated. Drastic spectral changes of aza-BODIPY compounds containing hydroxy group were observed in linear absorption spectra depending on basicity of solution. New bands in linear absorption spectra of phenolate form of these compounds appeared bellow 500nm and above 700nm in THF solution. These findings were caused by occurrence of the intramolecular charge transfer state in the phenolate form. Ultrafast pump probe spectroscopy experiments revealed that phenolic form shows only bleaching signal around 600nm. On the other hand, the phenolate form showed fast growing nonlinear absorption signals bellow 500nm and above 700nm regions in addition to the bleaching signal around 600nm. Intramolecular charge transfer state occurs above 700nm and the lifetime of this state is found on the order of ultrafast time scales. Since the excitation of the fluorescence experiments is at 600nm there is no fluorescence signal due to the relaxation of the energy through intramolecular charge transfer state. Aza-BODIPY compounds containing methoxy group did not show any two photon absorption properties due to weak electron-donating strength of methoxy group while aza-BODIPY compounds containing hydroxyl showed two photon absorption properties in wide spectral range (1200–1450nm). Our results also indicated that intramolecular charge transfer enhances two photon absorption properties. [Copyright &y& Elsevier]