Strong Absorption Cross Section Research Articles

Coherent field sensing of nitrogen dioxide.

We introduce a portable dual-comb spectrometer operating in the visible spectral region for atmospheric monitoring of NO2, a pollution gas of major importance. Dual-comb spectroscopy, combining key advantages of fast, broadband and accurate measurements, has been established in the infrared as a method for the investigation of atmospheric gases with kilometer-scale absorption path lengths. With the presented dual-comb spectrometer centered at 517 nm, we make use of the strong absorption cross section of NO2 in this spectral region. In combination with a multi-pass approach through the atmosphere, we achieve an interaction path length of almost a kilometer while achieving both advanced spatial resolution (90 m) and a detection sensitivity of 5 ppb. The demonstrated temporal resolution of one minute outperforms the standard chemiluminescence-based NO2 detector that is commercially available and used in this experiment, by a factor of three.

Synthesis, photophysical and electrochemical properties of π-conjugated pyrene based down-shifting molecules with fluorinated aryl groups

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 (λem) 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.

Panchromatic light funneling through the synergy in hexabenzocoronene-(metallo)porphyrin-fullerene assemblies to realize the separation of charges.

Here, we present a novel butadiyne-linked HBC-ethynyl-porphyrin dimer, which exhibits in the ground state strong absorption cross sections throughout the UV and visible ranges of the solar spectrum. In short, a unidirectional flow of excited state energy from the HBC termini to the (metallo)porphyrin focal points enables concentrating light at the latter. Control over excitonic interactions within, for example, the electron-donating porphyrin dimers was realized by complexation of bidentate ligands to set up panchromatic absorption that extends all the way into the near-infrared range. The bidentate binding motif was then exploited to create a supramolecular electron donor–acceptor assembly based on a HBC-ethynyl-porphyrin dimer and an electron accepting bis(aminoalkyl)-substituted fullerene. Of great relevance is the fact that charge separation from the photoexcited HBC-ethynyl-porphyrin dimer to the bis(aminoalkyl)-substituted fullerene is activated not only upon photoexciting the HBCs in the UV as well as the (metallo)porphyrins in the visible but also in the NIR. Implicit is the synergetic interplay of energy and charge transfer in a photosynthetic mimicking manner. The dimer and bis-HBC-ethynyl-porphyrin monomers, which serve as references, were probed by means of steady-state as well as time-resolved optical spectroscopies, including global target analyses of the time-resolved transient absorption data.

Sub-parts-per-trillion level sensitivity in trace gas detection by cantilever-enhanced photo-acoustic spectroscopy

An exceptional property of photo-acoustic spectroscopy is the zero-background in wavelength modulation configuration while the signal varies linearly as a function of absorbed laser power. Here, we make use of this property by combining a highly sensitive cantilever-enhanced photo-acoustic detector, a particularly stable high-power narrow-linewidth mid-infrared continuous-wave optical parametric oscillator, and a strong absorption cross-section of hydrogen fluoride to demonstrate the ability of cantilever-enhanced photo-acoustic spectroscopy to reach sub-parts-per-trillion level sensitivity in trace gas detection. The high stability of the experimental setup allows long averaging times. A noise equivalent concentration of 650 parts-per-quadrillion is reached in 32 minutes.

White-Emitting Protein Nanoparticles for Cell-Entry and pH Sensing

Facile synthesis of white-emitting, protein-based, metal-free, stable, nontoxic, and pH sensitive, advanced functional nanoparticles (GlowDots), as alternatives to quantum dots, is reported here. Controlled cross-linking of bovine serum albumin resulted in facile formation of spherical nanoparticles of 35 nm in diameter with a sharp size distribution (±10 nm), which were then conjugated with specific dyes to produce white-emitting particles with tunable excitation wavelengths. Chemical novelty is that the particle size, size distribution, stability, surface chemistry, and emission properties are under full chemical control where the size and absorption/emission properties are independently tuned. Up to 100 dye molecules were attached to each particle, on an average, and hence, particles acquired strong absorption cross-sections as well as high brightness. White fluorescence of GlowDots is strongly sensitive to pH over a range of pH 2–11, and pH-induced emission changes are fully reversible. The particles readily entered HeLa cells and emission color depended on particle location in the live cells, which is most likely due to the local environment surrounding the particles. These are the very first reports of white-emitting advanced functional nanoparticles that are biodegradable, sensitive to pH, and amenable for live cell imaging to probe the subcellular compartments.

Detection of plasmonic nanoparticles with full field-OCT: optical and photothermal detection.

Detecting the signal backscattered by nanoparticles immersed in highly scattering media such as biological tissue remains a challenge. In this article we report on the use of Full Field OCT (FF-OCT) to slice in depth in phantoms and in tissues in order a) to selectively observe the particles through the backscattered light at suitable wavelengths, and b) to detect the effects of the time-dependent response to full field optical heating through the strong absorption cross-section of these plasmonic nanoparticles. The analysis of the thermal wave behavior leads to the localization of the heat sources even when FF-OCT signals cannot reach the heated area.

Observation of Nanoscale Cooling Effects by Substrates and the Surrounding Media for Single Gold Nanoparticles under CW-Laser Illumination

Understanding the nanoscale heating-induced local thermal response is important but hampered by lack of information on temperatures at such small scales. This paper reports laser-induced heating and thermal equilibration of metal nanoparticles supported on different substrates and immersed in several media. We use single-particle spectroscopy to monitor nanoparticle temperature rises due to laser excitation. Because of changes in the refractive index of the surrounding medium, the scattering spectrum of the gold nanoparticles undergoes a shift that is related to the temperature of the system. We find that the temperature increase depends on both the surrounding medium and the supporting substrate. We furthermore model the nanoparticle temperature using a simplified 1-D heat conduction model with an effective thermal conductivity that takes both substrate and environment into account. The results from this model are also compared to a more detailed 2-D heat transfer analysis. The results presented here are quite new and important to many plasmonic nanoparticle applications where the strong absorption cross section of the nanoparticles leads to a significant temperature rise. In particular, the current work introduces an analysis that can be easily implemented to model the temperature of a nanoparticle supported on a substrate, as is the case in many single-particle measurements.

Significant increase in the water dispersibility of zinc phthalocyanine nanowires and applications in cancer phototherapy

The phototherapy is one of the widely accepted noninvasive clinical methodologies to eradicate cancer cells owing to its minimal side effects and high selectivity to the light of specific wavelength. As represented by photodynamic (PD) and photothermal (PT) therapy, the phototherapy requires light and photosensitizer to generate reactive oxygen species and heat, respectively. Zinc phthalocyanine (ZnPc) is one of the promising photosensitizers as it has a strong absorption cross-section in the spectral range of 650–900 nm that guarantees maximum tissue penetration. One critical issue in using Pc molecule, including ZnPc as a biocompatible sensitizer is the poor water solubility. To increase water solubility, various chemical modifications inducing hydrophilicity have been widely attempted to introduce various functional groups in the ZnPc backbone. We report that ZnPc nanowires (NWs) directly grown from ZnPc powder by vaporization–condensation–recrystallization process show surprisingly increased water dispersibility without any functionalization. The ZnPc NW solution exhibits highly efficient dual PD and PT effects upon the irradiation of near infrared (808 nm) laser. The dual phototherapeutic effect of ZnPc NW is proven to enhance cytotoxic efficiency according to both in vitro and in vivo experimental results. Hee Cheul Choi, Sang Ho Lee and co-workers have devised a way to improve the dispersibility of light-sensitive molecules in water. Using light to treat medical conditions, including tumours, can be less invasive and toxic than other approaches. Such photodynamic and photothermal therapies rely on a light-sensitive molecule — a photo-sensitizer — that is excited under irradiation to release either reactive oxygen species or heat, respectively, which in turn can destroy targeted cells. Most photo-sensitizers, however, suffer from poor solubility in aqueous physiological media, which hinders their applications in the body. This is the case for zinc phthalocyanine, a macrocyclic compound hosting a zinc atom in its central cavity. Rather than trying to alter its chemical composition, the researchers have now observed that converting the powder form into crystalline nanowires significantly increased its dispersibility in water. Furthermore, the nanowires were found to be promising for both photothermal and photodynamic therapies. Water-dispersed nanowires for phototherapy: Without passivation of any water-friendly functional groups in its backbone, one-dimensional zinc phthalocyanine nanowires show remarkably increased dispersibility in water. Upon irradiation with near infrared light, the zinc phthalocyanine nanowires exhibit dual photodynamic and photothermal properties, which enhance the cytotoxic efficiency against tumor cells.

Design of optically active nanoclusters of gold particles with mesostructured silica coating

Monodispersed, nanosized gold-mesoporous silica nanospheres in the size range 80–280 nm with specific optical properties are prepared in two steps: i) controlled aggregation of gold nanoparticles (GNP) in nanoclusters embedded in a uniform coating of amorphous silica, and ii) development of a porous regular and ordered silica shell by pseudomorphic transformation of the external layer. By careful manipulation of the synthesis variables, i.e., the concentration of co-solvent, surfactant and alkali, it is possible to obtain nanoparticles with controlled morphological and textural characteristics and desired optical behaviour. An optimized sample with most of the nanoparticles containing a multinucleus core made of 10 or more GNP shows a strong absorption cross-section in the near-infrared (NIR) region and a significant photothermal effect when irradiated with a λ = 808 nm laser diode module.

Nanocomposite Er–Ag silicate glasses

Particular attention has being given to metal–dielectric nanostructured materials, due to the well known surface plasmon resonance, described as the oscillation of the free electrons with respect to the ionic background of the nanoparticle when they are collectively excited by laser irradiation. It is claimed that metal nanoparticles can be used for increasing the intensity of the luminescence emitted by rare earth ions. This effect is attributed to the strong absorption cross section related to the surface plasmon excitation in noble-metal nanoparticles and/or to the large local field enhancement generated around the excited nanoparticles. In spite of the large amount of work published on this topic, the mechanism of optical amplification remains controversial. Here we present x-ray photoelectron spectra and transmission electron images together with photoluminescence absorption and emission measurements, with the aim of providing a better understanding of the effective role of silver as a sensitizer for erbium.

An hybrid organic–inorganic approach to erbium-functionalized nanodots for emission in the telecom window

A new class of hybrid materials for efficient laser emission and amplification in the 1.55 μm eye-safe telecommunication window has been designed, elaborated and characterized, based on lanthanide-doped yttrium oxide nanoparticle guests embedded in a polymer host matrix. The average size of these nanocrystals can be finely tuned by controlling the relative quantities of an organic fuel (glycine) with respect to the yttrium- and lanthanide-containing reactants involved in the combustion reaction leading to nanoparticle synthesis. Two complementary sensitizers have been added to Er/Y 2O 3 nanocrystals in order to improve the Erbium luminescence efficiency: cerium to increase population inversion between the emitting and the ground state by accelerating the de-excitation process from the 4I 11/2 initially uppermost excited state at 980 nm down to 4I 13/2 state emitting around 1.55 μm, and ytterbium to improve the pumping efficiency of the material owing to its strong absorption cross section at 980 nm and subsequent efficient energy transfer towards the 4I 11/2 state of erbium ion. Y 2O 3 nanoparticles with an optimized erbium–ytterbium composition have been incorporated in a PMMA polymer matrix, resulting in a hybrid amorphous material displaying high gain coefficient values (up to 30 cm −1 as from Amplified Spontaneous Emission experiments) upon moderate 980 nm pumping intensities. These materials open attractive perspectives in the domain of polymer-based telecom amplifiers, with the additional asset of multifunctional properties whereby gain originating from the inorganic Y 2O 3 nanocrystals can be associated to nonlinear responses attached to an adequately functionalized polymer host matrix.

Encapsulation of Magnetic and Fluorescent Nanoparticles in Emulsion Droplets

Oils containing both fluorescent semiconductor and magnetic oxide nanoparticles are used to produce oil in water emulsions. This technique produces oil droplets with homogeneous fluorescence and high magnetic nanoparticle concentrations. The optical properties of the oil droplets are studied as a function of the droplet sizes for various concentrations of fluorescent and magnetic nanoparticles. For all concentrations tested, we find a linear variation of the droplet fluorescent intensity as a function of the droplet volume. For a given size and a given quantum dot (QD) concentration, the droplet fluorescence intensity drops sharply as a function of the magnetic nanoparticle concentration. We show that this decrease is due mainly to the strong absorption cross section of the magnetic nanoparticles and to a lesser extent to the dynamic and static quenching of the QD fluorescence. The role of the iron oxide nanoparticle localization in the droplet (surface versus volume) is also discussed.

Correlation between rare-earth oscillator strengths and rare-earth–valence-band interactions in neodymium-dopedYMO4(M=V,P, As),Y3Al5O12,andLiYF4matrices

${\mathrm{Nd}}^{3+}{:\mathrm{Y}\mathrm{V}\mathrm{O}}_{4}$ is one of the more promising laser hosts for micro and diode-pumped solid-state lasers. At room temperature, ${\mathrm{Nd}}^{3+}$ ions in this matrix exhibit strong absorption cross sections sixfold higher than in ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}.$ The neodymium oscillator strengths are measured in $\mathrm{Y}M{\mathrm{O}}_{4}$ ($M=\mathrm{V},$ P, As), ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12},$ and ${\mathrm{LiYF}}_{4}$ hosts, and they increase in the sequence ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}{l\mathrm{LiYF}}_{4}{l\mathrm{YAsO}}_{4}{l\mathrm{YPO}}_{4}{l\mathrm{YVO}}_{4}.$ This paper is an attempt to correlate these variations with covalent interactions between neodymium $4f,5d$ levels and valence-band levels. The strength of orbital interactions between $4f$ levels and valence-band states is estimated from the analysis of $3d$ x-ray photoemission spectra of ${\mathrm{Nd}}^{3+}$ ions. A two-step model is derived, in which $5d$ admixture into the $4f$ levels of the rare earth occurs via the valence-band levels. This model shows that the oscillator strengths increase with the Nd $4f$-valence-band interactions.