Infrared Emission Bands Research Articles

Asphaltenes as model compounds of the UIBs/AIBs detected in various astrophysical objects. Part 3: Petroleum asphaltenes high energy radiation processed

The asphaltenes isolated from a heavy petroleum fractions were subjected to radiation damage using either neutron bombardment (corpuscular radiation simulating cosmic rays) or γ-rays (high energy electromagnetic radiation). The purpose was to study how the radiation damage changes the spectral, thermal properties and other properties of the asphaltenes in a possible simulation of the destiny of these molecules exposed to the harsh circumstellar and interstellar medium. In fact, the asphaltenes were proposed as model molecules matching the MAONs model (mixed aromatic/aliphatic organic nanoparticles), the supposed carriers of the unidentified infrared bands known also as aromatic infrared bands or the unidentified infrared bands which represent a series of discrete infrared emission bands detected in numerous and different astrophysical environments. Thus, the pristine and radiation-damaged asphaltenes were studied with scanning electron microscopy, FTIR spectroscopy, electronic absorption spectroscopy, thermogravimetric analysis (TGA-DTG) and electron spin resonance.

Unidentified Infrared Discrete Emission Bands

Unidentified Infrared emission bands (UIBs) are infrared discrete emissions from circumstellar regions, interstellar media (ISM), star-forming regions, and extragalactic objects for which the identity of the emitting materials is unknown. The main infrared features occur around peaks at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with the photon’s rest energy at the peaks 0.376, 0.200, 0.161, 0.144, 0.111, and 0.098 eV, respectively. The UIB emission phenomenon has been studied for about forty five years. The prevailing hypothesis is that the materials responsible for UIB are polycyclic aromatic hydrocarbon (PAH) molecules. PAHs are thought to be one of the main forms in which carbon exists in space. And yet, not a single member of this group of compounds had been identified in space definitively until now [1]. In frames of Hypersphere World-Universe Model (WUM), we introduced Dark Matter (DM) particles, named DIONs, with the rest energy 0.199 eV and an energy density of 68.8% of the total energy density of the World. DIONs compose Outer shells of DM Supercluster’s Cores—the main objects of the World [2]. In this paper, we give an explanation of UIB emission based on the self-annihilation of DM particles DIONs and biDIONs (DIONs pairs) with a rest energy about 0.38 eV that depends on the binding energy. To the best of our knowledge, WUM is the only cosmological model in existence that is consistent with UIB emission phenomenon.

Enhanced mid-infrared emission of Pr3+ ions in solids through a "3-for-1" excitation process - quantified.

Evidence is presented that a "three-for-one" process based on two cross-relaxations between Pr3+ ions efficiently populates the mid-infrared-emitting 3H5 manifold in a Pr3+-doped low-maximum-phonon-energy host. The concentration dependence of infrared fluorescence spectra and lifetimes of polycrystalline Pr:KPb2Cl5 initially excited to the 3F3,4 manifolds indicate that the 3500-5500-nm fluorescence becomes strongly favored over shorter-wavelength infrared emission bands in the higher-concentration sample. The strong concentration dependence of the 3F3 and 3H6 manifold lifetimes suggests that both of these decay by cross-relaxation processes, resulting in more than one ion excited to 3H5 for each ion initially excited to 3F3. Indeed, modeling and accounting for all possible decay paths indicate that, on average, about 2.3 ions are excited to 3H5 for each initially-excited ion. This confirms that the three-for-one excitation process must occur and contribute significantly to the total excitation efficiency. These results indicate that the two distinct cross-relaxation processes observed between Pr ions result in substantially higher excitation quantum efficiency, 230%, than any ever reported in rare-earth doped materials.

Asphaltenes as model compounds of the UIBs/AIBs detected in various astrophysical objects. Part 1 – Petroleum asphaltenes carbonization

The Unidentified Infrared bands (UIBs or UIRs) known also as Aromatic Infrared Bands (AIBs) represent a series of discrete infrared emission bands detected in numerous and very different astrophysical objects. The carriers of these infrared bands have not yet unambiguously identified. The MAONs model proposes that the carriers of the UIBs could be described by an “average” chemical structure consisting of mixed aromatic-aliphatic organic nanoparticles (MAONs) and containing also heteroatoms such as N, S and O. Asphaltenes are matching quite well the MAONs model and in this work a series of selected asphaltenes from petroleum were carbonized at 700 °C in sealed crucible under inert atmosphere leading to a carbon coke. Both the starting asphaltenes and the result of their carbonization were studied with FT-IR spectroscopy. It is shown that the asphaltenes and the resulting coke can be considered excellent model compounds for the UIBs’ carriers and their evolution because of thermal and radiation processing of the latter in the harsh space environment.

Detection of interstellar H2CCCHC3N

Context. The chemical pathways linking the small organic molecules commonly observed in molecular clouds to the large, complex, polycyclic species long suspected of being carriers of the ubiquitous unidentified infrared emission bands remain unclear. Aims. To investigate whether the formation of mono- and polycyclic molecules observed in cold cores could form via the bottom-up reaction of ubiquitous carbon-chain species with, for example, atomic hydrogen, a search is made for possible intermediates in data taken as part of the GOTHAM (GBT Observations of TMC-1: Hunting for Aromatic Molecules) project. Methods. Markov chain Monte Carlo (MCMC) source models were run to obtain column densities and excitation temperatures. Astrochemical models were run to examine possible formation routes, including (a) a novel grain-surface pathway involving the hydrogenation of C6N and HC6N, (b) purely gas-phase reactions between C3N and both propyne (CH3CCH) and allene (CH2CCH2), and (c) via the reaction CN + H2CCCHCCH. Results. We report the first detection of cyanoacetyleneallene (H2CCCHC3N) in space toward the TMC-1 cold cloud using the Robert C. Byrd 100 m Green Bank Telescope. Cyanoacetyleneallene may represent an intermediate between less-saturated carbon chains, such as the cyanopolyynes, that are characteristic of cold cores and the more recently discovered cyclic species, such as cyanocyclopentadiene. Results from our models show that the gas-phase allene-based formation route in particular produces abundances of H2CCCHC3N that match the column density of 2 × 1011 cm−2 obtained from the MCMC source model, and that the grain-surface route yields large abundances on ices that could potentially be important as precursors for cyclic molecules.

The unidentified infrared bands and the spectrum of atomic hydrogen

This letter compares the footprints on a spectral axis of the main unidentified infrared emission bands (UIBs) with the recombination lines of atomic hydrogen. The comparison shows striking correspondences, suggesting that atomic hydrogen may be involved in the production of UIBs.

Unexplained spectral phenomena in the interstellar medium: an introduction

There exists a number of astronomical spectral phenomena that have remained unidentified after decades of extensive observations. The diffuse interstellar bands, the 220 nm feature, unidentified infrared emission bands, extended red emissions, and 21 and 30 μm emission features are seen in a wide variety of astrophysical environments. The strengths of these features suggest that they originate from chemical compounds made of common elements, possibly organic in nature. The quest to understand how such organic materials are synthesized and distributed across the Galaxy represents a major challenge to our understanding of the chemical content of the Universe.

A Spectroscopic View on Cosmic PAH Emission

ConspectusPolycyclic aromatic hydrocarbon molecules (PAHs) are ubiquitously present at high abundances in the Universe. They are detected through their infrared (IR) fluorescence UV pumped by nearby massive stars. Hence, their infrared emission is used to determine the star formation rate in galaxies, one of the key indicators for understanding the evolution of galaxies. Together with fullerenes, PAHs are the largest molecules found in space. They significantly partake in a variety of physical and chemical processes in space, influencing star and planet formation as well as galaxy evolution.Since the IR features from PAHs originate from chemical bonds involving only nearest neighbor atoms, they have only a weak dependence on the size and structure of the molecule, and it is therefore not possible to identify the individual PAH molecules that make up the cosmic PAH family. This strongly hampers the interpretation of their astronomical fingerprints. Despite the lack of identification, constraints can be set on the characteristics of the cosmic PAH family thanks to a joint effort of astronomers, physicists, and chemists.This Account presents the spectroscopic properties of the cosmic PAH emission as well as the intrinsic spectroscopic properties of PAHs and astronomical modeling of the PAH evolution required for the interpretation of the cosmic PAH characteristics. We discuss the observed spectral signatures tracing PAH properties such as charge, size, and structure and highlight the related challenges. We discuss the recent success of anharmonic calculations of PAH infrared absorption and emission spectra and outline the path forward. Finally, we illustrate the importance of models on PAH processing for the interpretation of the astronomical data in terms of the charge balance and PAH destruction.Throughout this Account, we emphasize that huge progress is on the horizon on the astronomical front. Indeed, the world is eagerly awaiting the launch of the James Webb Space Telescope (JWST). With its incredible improvement in spatial resolution, combined with its complete spectral coverage of the PAH infrared emission bands at medium spectral resolution and superb sensitivity, the JWST will revolutionize PAH research. Previous observations could only present spectra averaged over regions with vastly different properties, thus greatly confusing their interpretation. The amazing spatial resolution of JWST will disentangle these different regions. This will allow us to quantify precisely how PAHs are modified by the physical conditions of their host environment and thus trace how PAHs evolve across space. However, this will only be achieved when the necessary (and still missing) fundamental properties of PAHs, outlined in this Account, are known. We strongly encourage you to join this effort.

Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering.

Unidentified infrared emission bands are ubiquitous in many astronomical sources. These bands are widely, if not unanimously, attributed to collective emissions from polycyclic aromatic hydrocarbon (PAH) molecules, yet no single species of this class has been identified in space. Using spectral matched filtering of radio data from the Green Bank Telescope, we detected two nitrile-group-functionalized PAHs, 1- and 2-cyanonaphthalene, in the interstellar medium. Both bicyclic ring molecules were observed in the TMC-1 molecular cloud. In this paper, we discuss potential in situ gas-phase PAH formation pathways from smaller organic precursor molecules.

Gas-phase spectroscopic characterization of neutral and ionic polycyclic aromatic phosphorus heterocycles (PAPHs)

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) constitute an essential family of compounds in interstellar (ISM) and circumstellar (CSM) media. Recently, formation routes for the corresponding polycyclic aromatic phosphorus heterocycles (PAPHs) in astrophysical environments have been proposed. In order to contribute to a better understanding of the phosphorus chemistry in the ISM, infrared (IR) spectra and selected properties of PAPHs were computed at the density functional theory level for neutral, cationic, and anionic species. Our results reveal that several protonated PAPHs do not have planar backbones, and all species have permanent dipole moments between 2D and 4D. Closed-shell PAPHs have similar ionization potentials compared to the parent PAHs, below the Lyman threshold limit. In addition, all PAPHs show positive electron affinities higher than those of PAHs. Protonation preferably occurs on the heteroatom but with lower proton affinities than those of the corresponding nitrogen analogues (polycyclic aromatic nitrogen heterocycles). In general, neutral species have similar IR spectra profile with the most intense bands around 800 cm−1 (12.5 μm) related to C−H wagging. Charge and protonation affect the IR spectra mainly by decreasing the intensities of these modes and increasing the ones between 1000 (10.0 μm) and 1800 cm−1 (5.6 μm). The P−H stretching appears in a different spectral region, between 2300 (4.3 μm) and 2700 cm−1 (3.7 μm). Our results are discussed in the context of distinct sources where PAHs and phosphorus are detected. PAPHs, in particular the coronene derivatives, can contribute to the unidentified infrared emission band at 6.2 μm.

Impact of Tb4+ and morphology on the thermal evolution of Tb-doped TiO2 nanostructured hollow spheres and nanoparticles

Tb-doped TiO2 hollow spheres (HSs) in the range 0.0–2.0 at.% have been synthesized by the first time to the best of our knowledge. The HSs are compared with nanoparticles (NPs) to evaluate the impact of morphology on their physicochemical and photoluminescence (PL) behavior upon increasing calcination temperature. After calcination at 550 °C, the particles are anatase with a primary average size of 10.0 ± 0.2 nm for the NPs and 12.0 ± 0.2 nm for those that form the micron sized hollow spheres of 1.8 ± 0.2 μm diameter and ca. 64 nm shell thickness. The temperature of the anatase–rutile transition is found to be strongly dependent on the presence of Tb as well as on morphology. Contrarily to the usual stabilization of anatase when doping with trivalent rare-earth ions, the transition temperature is reduced when doping with Tb. The rutile phase is further favored for the HSs compared to the NPs probably related to the low density of the HSs and/or a more efficient packing density and/or a bigger crystal size of the nanoparticles that form those spheres with respect to the packing and the size of the NPs and/or the crystal size of the nanoparticles of the HSs with respect to the size of the NPs. Only a slight unit-cell volume increase for the anatase structure is observed upon Tb doping, in both the NPs and in the HSs, contrary to the expected increment due to the larger ionic radius of Tb3+ compared to Ti4+. In addition, the intensity of the characteristic f-f Tb3+ emission bands is extremely weak both in the anatase and rutile phases. The transition is accompanied with the emergence of an infrared emission band centered at 810 nm related to the formation of defects during the structural transformation providing deep levels in the gap that partly quench the f-f emissions in the rutile phase. The results are consistent with the presence of Tb in both +3 and +4 valence states. XPS measurements confirmed the presence of Tb3+ as well as of Tb4+ in both HSs and NPs. The large fraction of Tb4+ present in the samples originates the weak f-f emission intensity, an only slight increase of the cell parameters and the destabilization of the anatase phase.

Nd3+-doped LiBaPO4 phosphors for optical temperature sensing within the first biological window: A new strategy to increase the sensitivity

In this work, powders of LiBaPO4:Nd3+ were synthesized by the sol–gel method using PVA as a chelating agent. X-ray diffraction indicates a tridymite structure with a hexagonal unit cell and space group P63. SEM images show that the samples have particles of different sizes with the majority varying between 5 and 20 μm. Under 532 nm excitation, four infrared emission bands were observed, with maxima at 749.9, 802.4, 873.2 and 953.4 nm assigned to the transitions from 4F7/2, 4F5/2, 4F3/2 to 4I9/2 and from 4F5/2 to 4I11/2. The performance of this material aiming optical thermometry based on the fluorescence intensity ratio methodology (FIR) was investigated within the range from 294 to 373 K, suitable for applications in biological systems. Under visible excitation, sensor performance is comparable to previously investigated Nd schemes. However, the sensing performance under infrared excitation was strongly enhanced by exploiting the FIR associated to the 4F5/2 → 4I11/2 and 4F3/2 → 4I9/2 transitions. The obtained relative sensitivity with this approach is one order of magnitude higher when compared with other Nd-doped materials excited in the infrared. These results suggest that the analyzed material can be used for application in temperature sensing of biological systems exploring the first biological window.

Spectroscopic and luminescent properties of the lithium tetraborate glass co-doped with Tm and Ag

Spectroscopic properties of the Tm3+ (4f12, 3H6) ions in Tm-doped and Tm–Ag co-doped glasses with Li2B4O7 (or Li2O–2B2O3) basic composition are studied. All investigated glasses show intense blue, red, and infrared emission bands of the Tm3+ ions. Experimental and theoretical oscillator strengths (fexp and fcal), Judd–Ofelt intensity parameters (Ω2, Ω4, Ω6) and radiative properties such as probabilities of radiative transition (Arad), branching ratios (β), radiative lifetimes (τrad), and quantum efficiencies (η) of the Tm3+ luminescence in the Li2B4O7:Tm and Li2B4O7:Tm,Ag were calculated. Presence of the Ag0 (4d105s1, 2S1/2) and Ag2+ (4d9, 2D5/2) paramagnetic centres and their aggregates in the Li2B4O7:Tm,Ag glass was confirmed by electron paramagnetic resonance. Luminescence spectra and decay kinetics of the Ag+ (4d10, 1S0) ions and small non-plasmonic Ag aggregates were registered and discussed. Increasing of quantum efficiency and yield of the Tm3+ luminescence in the Li2B4O7:Tm,Ag glass is explained by energy transfer from Ag species to the Tm3+ ions.

Infrared emission bands and thermal effects for 440-nm-emitting GaN-based laser diodes

Broad emission bands due to defects in (In,Ga,Al)N laser diodes operating at 440 nm are investigated using continuous-wave and pulsed currents. In addition to known yellow–green and short-wave infrared bands, defect emissions were observed even in the medium-wave infrared range. A separation from thermal radiation is possible. When using pulsed currents, a super-linearly increasing emission occurs at ∼1150 nm, which could be attributed to amplified spontaneous emission mainly due to the electroluminescence of deep defects in the optically active region. These results may be useful in interpreting the output power bottleneck of GaN-based lasers compared to mature GaAs-based lasers.

Synthesis and Characterization of Aromatic Poly(azomethine ether)s with Different meta- and para-Phenylene Linkage Contents

New aromatic poly(azomethine ether)s (PAMEs) bearing different meta- and para-phenylene linkage ratios in the main chains were synthesized via solution polycondensation reactions of terephthalaldehyde and/or isophthaldehyde with 3,4′-diaminodiphenyl ether. The molecular structures, thermal stability, thermo-mechanical and optical properties of the synthesized PAME homopolymers and copolymers were investigated by using FT-IR, TGA, DMA, and UV-visible/ fluorescence spectroscopy, respectively. The synthesized PAMEs were characterized to be thermally stable up to ~400 °C under nitrogen or air atmosphere and to have high char residues of above 55 % at 800 °C under nitrogen condition. The DMA data revealed that the glass transition temperatures of PMAEs are in the range of 150–200 °C, depending on the relative contents of meta- and para-phenylene linkages. The maximum absorption wavelength of transparent yellowish PAME films was detected at 410±10 nm. In addition, all PAME films exhibited a broad visible emission band at 500–800 nm and two infrared emission bands at 800–1400 nm. The synthesized PAMEs with high thermal stability and thermo-mechanical performance can be thus used as functional polymeric materials for technical fibers, optoelectronic films, and carbon fiber precursors.

Discriminating Cys from GSH/H2S in vitro and in vivo with a NIR fluorescent probe

Biothiols play a prominent role in physiological and pathological processes as reactive sulfur species (RSS), which are closely related to the pathways of metabolism of living animals. By reason of their similar chemical structure and properties, it is challenging to distinguish biological mercaptans from each other in living systems. Herein, a NIR probe (NN) for effectively distinguishing cysteine (Cys) from glutathione (GSH)/hydrogen sulfide (H2S) using a dual-channel responsive mode in vitro and in vivo were developed. NN performs no fluorescence characteristics in the visible to NIR range. Upon treatment with Cys, the system generates significant fluorescence enhancement in both green and near infrared emission bands, while encounter of GSH/H2S generates the increasing of fluorescence only in the near infrared region. In addition, the probe NN also exhibits excellent selectivity, stability, low cytotoxicity as well as low detection limit (0.05 μM for Cys, 0.11 μM for GSH and 0.02 μM for H2S). More importantly, integrating these excellent attributes into a single molecule make it possible to discriminate Cys from GSH/H2S in vivo for the first time.

Up/Down-Conversion Luminescence of Er3+ Doped ZrO2·Al2O3 Powder

ZrO2·Al2O3:Er powder was synthesized by the conventional solid-state reaction method. All the synthesized materials were monoclinic structure of ZrO2 (m-ZrO2) and Al2O3 phases. Scanning electron microscope images showed the spherical particles with diameter of ∼ (30–200) nm. The down-conversion luminescence spectra excited by 380 nm shows near infrared emission band is centered at 1540 nm, corresponding to the transitions of 4I13/2–4I15/2 of Er3+ ions. Under the excitation of a 976 nm laser diode, the up-conversion luminescence spectra of the samples show a red emission band at ∼ 680 nm and a green emission band at ∼ 565 nm, corresponding to the transitions of 4F9/2–4I15/2, 4S3/2–4I15/2, of Er3+ ions, respectively. The dependence of up and down-conversion luminescence properties on dopant concentrations, annealing temperature and Al2O3 concentrations are investigated. These results suggested that this phosphor is a very promising material for light emission and bioimaging.

Photoluminescence of Yb3+/Ce3+ co-doped aluminosilicate glasses under ultraviolet irradiation

The photoluminescence and decay properties of Yb3+/Ce3+ co-doped aluminosilicate glasses were investigated under ultraviolet irradiation. A strong excitation band was ascribed to 4f → 5d transitions of Ce3+ ions. A broad ultraviolet-visible emission band belonged to 5d → 4f transitions of Ce3+ ions and oxygen-deficient centers (ODCs) in the host matrix, and the visible-near infrared emission band was attributed to non-bridging oxygen hole centers. Comparative tests of the core composition were performed. The results showed Yb2O3 and the ODCs played a crucial role on ultraviolet-visible emission band. ODCs rather than Ce3+ ions were responsible for the 1–35 μs lifetime decay of the ultraviolet-visible emission, but had no contribution to the longer decay lifetimes (77.58 μs) for Ce-free Yb3+-doped glasses. A complex schematic energy-level diagram including the electron transfer mechanism such as Ce3+-Yb3+ → Ce4+-Yb2+, the cooperative up- and down-conversion processes was proposed to describe different luminescence mechanisms UV-expose.

Infrared spectrum of hydrogenated corannulene rim-HC20H10 isolated in solid para-hydrogen.

Hydrogenated polycyclic aromatic hydrocarbons have been proposed to be carriers of the interstellar unidentified infrared (UIR) emission bands and the catalysts for formation of H2; spectral characterizations of these species are hence important. We report the infrared (IR) spectrum of mono-hydrogenated corannulene (HC20H10) in solid para-hydrogen (p-H2). In experiments of electron bombardment of a mixture of corannulene and p-H2 during deposition of a matrix at 3.2 K, two groups of spectral lines increased with time during maintenance of the matrix in darkness after deposition. Lines in one group were assigned to the most stable isomer of hydrogenated corannulene, rim-HC20H10, according to the expected chemistry and a comparison with scaled harmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method. The lines in the other group do not agree with predicted spectra of other HC20H10 isomers and remain unassigned. Alternative hydrogenation was achieved with H atoms produced photochemically in the infrared-induced reaction Cl + H2 (v = 1) → H + HCl in a Cl2/C20H10/p-H2 matrix. With this method, only lines attributable to rim-HC20H10 were observed, indicating that hydrogenation via a quantum-mechanical tunneling mechanism produces preferably the least-energy rim-HC20H10 regardless of similar barrier heights and widths for the formation of rim-HC20H10 and hub-HC20H10. The mechanisms of formation in both experiments are discussed. The bands near 3.3 and 3.4 µm of rim-HC20H10 agree with the UIR emission bands in position and relative intensity, but other bands do not match satisfactorily with the UIR bands.

Infrared spectra of protonated and hydrogenated corannulene (C20H10) and sumanene (C21H12) using matrix isolation in solid para-hydrogen – implications for the UIR bands

AbstractPolycyclic aromatic hydrocarbons (PAH) and their derivatives, including protonated and cationic species, are suspected to be carriers of the unidentified infrared (UIR) emission bands observed from the galactic and extragalactic sources. We investigated the infrared (IR) spectra of protonated nonplanar PAHs: corannulene (C20H10) and sumanene (C21H12), that are regarded as a fragments of a fullerene,C60. The protonated corannulene H+ C20H10 and sumanene H+ C21H12 were produced in seperate experiments by bombarding a mixture of corannulene/sumanene and para-hydrogen (p-H2) with electrons during deposition at 3.2 K. During maintenance of the electron-bombarded matrix in darkness the intensities of IR lines of protonated corannulene decreased because of neutralization by electrons that were slowly released from the trapped sites whereas the hydrogenated species were produced. The observed lines were classified into several groups according to their responses to darkness and secondary irradiation at 365 nm/385 nm LEDs. Spectral assignments were derived based on a comparison of the observed spectra with those predicted with the B3PW91/6-311+ +G(2d,2p) method. The observed IR spectrum of hub-H+ C20H10, the most stable protonated isomer, resembles several bands of the Class-A UIR bands.