Measurements Of Emission Spectra Research Articles

Dry reforming of methane in a temperature-controlled dielectric barrier discharge reactor: disclosure of reactant effect

Plasma-assisted dry reforming of methane has attracted much research attention because this process simultaneously utilizes greenhouse, methane and carbon dioxide, to produce hydrogen-rich syngas at a relative low temperature. Although it is generally recognized that the gas composition of reactant has great effect on the methane conversion and products distribution, systematic studies that clarify the roles that electron-induced chemistry and thermochemistry play are needed for a full understanding of reactant effect. Here, we compared the reforming performance by varying the ratio of CO2/CH4 or O2/CH4 at the similar reduced field intensity (E/N) in a temperature-controlled dielectric barrier discharge reactor to elaborate the role of electron-induced chemistry and thermo-chemistry in the dry reforming process. By conducting optical emission spectrum measurement, the enrichment of O atoms was observed at the increased CO2/CH4 or O2/CH4 ratios. At T = 293 K, methane conversion was only dependent on the electron-induced chemistry regardless of the specific reactant gas composition. At a relative high temperature condition, however, thermochemistry could become pronounce when sufficient O atoms were added into the dry reforming process. In contrast, the chemical pathways to the products were overall controlled by the thermochemistry at the tested background temperatures. Due to the conversion of carbon-based products into the carbon dioxide, the conversion of carbon dioxide was influenced by the thermochemistry when the concentration of O atoms was high. Our findings may improve the understanding of reactant effect and the designs of plasma-reformer.

Opto-thermal Radiometry for Detection of Surface Contamination

The aim of this work is to conduct a proof-of-concept study on detection of surface contamination by biological and chemical agents using opto-thermal transient emission radiometry (OTTER). OTTER is an infrared remote sensing technology that has been developed in our research group for skin measurements. It is based on the measurement of laser-induced transient thermal emission spectra in the infrared fingerprint region, and has advantages of non-contact, non-invasive, spectroscopic in nature, and can work on arbitrary surfaces of any materials. In this paper, two types of experiments were conducted, different ingredients on the surface of a sample material and different ingredients on the skin surface. The results show that by measuring the OTTER signal at different detection wavelengths, e.g., 6.05 μm, 6.48 μm, 7.79 μm, 8.5 μm, 9.5 μm, 11.5 μm, 13.1 μm, it is possible to differentiate from skin and skin with different ingredients on the surface. The next step is to develop mathematical models and analytical algorithms to quantify the ingredient concentration on the surface.

Enhanced ~2.9 μm mid-infrared emissions of Ho3+/Yb3+ co-doped Na5Y9F32 single crystal introduced by Pr3+ ions

A novel Na5Y9F32 single crystals tri-doped with fixed ~0.8 mol% Ho3+, ~1 mol% Yb3+ and various Pr3+ from 0 to 0.8 mol% were successfully grown by a modified Bridgman method for 2.9 μm mid-infrared application. The effects of Pr3+ ion on the 2.9 μm emission was investigated systematically with the help of the absorption spectra, emission spectra and fluorescence decay curves. The emission intensity at ~2.9 μm of Ho3+: 5I6 → 5I7 was enhanced gradually as increase of Pr3+ concentration from 0 to 0.8 mol% under excitation of 980 nm laser diode (LD). The maximum emission cross-section at ~2.9 μm was calculated to be 5.62 × 10−20 cm2 according to the measured emission spectra. The energy transfer mechanism among Ho3+, Yb3+ and Pr3+ was studied. When the Pr3+ ion concentration reached 0.8 mol%, the energy conversion efficiencies for Ho3+: 5I7 → Pr3+: 3F2 and Ho3+: 5I6 → Pr3+: 3F4 were estimated about ~51.76% and ~15.73%, respectively. A remarkably augmented conversion process of Ho3+: 5I7 → Pr3+: 3F2 by the introduction of Pr3+ ion into Ho3+/Yb3+ system results into the enhancement of ~2.9 μm emission. The Pr3+ ion takes as an effective deactivation of the Ho3+ ion in the Na5Y9F32 single crystal. The Pr3+/Ho3+/Yb3+ tri-doped Na5Y9F32 single crystals may become a new choice for ~2.9 μm mid-infrared solid-state laser due to its both excellent optical properties and chemical stability.

Measurement and analysis of emission spectrum of laser-produced Ni plasma in the range of 7-14 nm

SynopsisWe measured and analyzed the emission spectrum of laser-produced Ni plasma in the range of 7-14 nm. The dominant transition arrays were identified as 3p63dn−3p63dn−1f and 3p53dn+1−3p53dn4f from Ni6+ to Ni9+ ions with aid of the Hartree-Fock calculations with configuration interaction effects. The plasma parameters have been obtained by comparison of experimental and simulated spectrum based on a steady-state collisional-radiative (CR) model.

Galactic diffuse gamma-ray emission at TeV energy

Context. Measuring the diffuse Galactic γ-ray flux in the TeV range is difficult for ground-based γ-ray telescopes because of the residual cosmic-ray background, which is higher than the γ-ray flux by several orders of magnitude. Its detection is also challenging for space-based telescopes because of low signal statistics. Aims. We characterise the diffuse TeV flux from the Galaxy using decade-long exposures of the Fermi Large Area Telescope. Methods. Considering that the level of diffuse Galactic emission in the TeV band approaches the level of residual cosmic-ray background, we estimated the level of residual cosmic-ray background in the SOURCEVETO event selection and verified that the TeV diffuse Galactic emission flux is well above the residual cosmic-ray background up to high Galactic latitude regions. Results. We study spectral and imaging properties of the diffuse TeV signal from the Galactic plane. We find much stronger emission from the inner Galactic plane than in previous HESS telescope estimates (lower bound). We also find a significant difference in the measurement of the Galactic longitude and latitude profiles of the signal measured by Fermi and HESS. These discrepancies are presumably explained by the fact that regions of background estimate in HESS have non-negligible γ-ray flux. Comparing Fermi measurements with those of ARGO-YBJ, we find better agreement, with the notable exception of the Cygnus region, where we find much higher flux (by a factor 1.5). We also measure the TeV diffuse emission spectrum up to high Galactic latitude and show that the spectra of different regions of the sky have spectral slopes consistent with Γ = 2.34 ± 0.04, which is harder than the slope of the locally observed spectrum of cosmic rays with energies 10–100 TeV, which produce TeV diffuse emission on their way through the interstellar medium. We discuss the possible origin of the hard slope of the TeV diffuse emission. Conclusions. Fermi/LAT provides reliable measurements of the diffuse Galactic emission spectrum in the TeV range, which are almost background free at low Galactic latitudes. The diffuse flux becomes comparable to the residual cosmic-ray background at Galactic latitudes |b| > 50°. Its measurement in these regions might suffer from systematic uncertainty stemming from the uncertainty of our phenomenological model of the residual cosmic-ray background in the Pass 8 Fermi/LAT data.

Learning Set Representations for LWIR In-Scene Atmospheric Compensation

Atmospheric compensation of long-wave infrared (LWIR) hyperspectral imagery is investigated in this article using set representations learned by a neural network. This approach relies on synthetic at-sensor radiance data derived from collected radiosondes and a diverse database of measured emissivity spectra sampled at a range of surface temperatures. The network loss function relies on LWIR radiative transfer equations to update model parameters. Atmospheric predictions are made on a set of diverse pixels extracted from the scene, without knowledge of blackbody pixels or pixel temperatures. The network architecture utilizes permutation-invariant layers to predict a set representation, similar to the work performed in point cloud classification. When applied to collected hyperspectral image data, this method shows comparable performance to Fast Line-of-Sight Atmospheric Analysis of Hypercubes-Infrared (FLAASH-IR), using an automated pixel selection approach. Additionally, inference time is significantly reduced compared to FLAASH-IR with predictions made on average in 0.24 s on a 128 pixel by 5000 pixel data cube using a mobile graphics card. This computational speed-up on a low-power platform results in an autonomous atmospheric compensation method effective for real-time, onboard use, while only requiring a diversity of materials in the scene.

A long lifetime ratiometrically luminescent tetracycline nanoprobe based on Ir(III) complex-doped and Eu3+-functionalized silicon nanoparticles

Different from fluorescent dyes-doped or carbon materials-based ratiometric tetracycline nanoprobes, herein, a new Ir(III) complex-doped and europium(III) ion (Eu3+)-functionalized silicon nanoparticles (Ir(III)@SiNPs-Eu3+) with long luminescent lifetimes was firstly fabricated for selective detection of tetracycline (TC) in complex systems through time-resolved emission spectra (TRES) measurement. In the presence of TC, the red phosphorescence of Eu3+ is greatly enhanced by adsorption energy transfer emission (AETE) of TC, while the strong green luminescence of Ir(III)@SiNPs is quenched by the inner filtration effect (IFE) of TC. Based on these striking emission changes, Ir(III)@SiNPs-Eu3+ can sensitively detect TC in the linear range of 0.01–20 μM with a detection limit of 4.9 × 10–3 μM. Benefitting from the long lifetime of Ir(III)@SiNPs-Eu3+, the nanoprobe demonstrates excellent TC detection performance through TRES in high background system of 5 % human serum. Furthermore, the formed Ir(III)@SiNPs-Eu3+/TC complex can be used to sensitively recognize Hg2+ via a ratiometric luminescence mode. Notably, the cytotoxicity of Ir(III)@SiNPs-Eu3+ is very low and thus the sensitive monitoring the detection of Ir(III)@SiNPs-Eu3+ to TC and Hg2+ also works well in porcine renal cells, demonstrating high application potential in real samples.

The Luminescence Properties of Sm3+ or Tb3+ —doped Lu3Ga2Al3O12 Phosphors for X-ray Imaging

Sm3+ or Tb3+ -doped Lu3Ga2Al3O12 phosphors were synthesized by using a solid-state reaction method with Lutetium oxide, gallium oxide and aluminum oxide as host materials, samarium oxide and terbium oxide as doping materials. The mixed powders were sintered at 1500 °C for 5 hours by using a horizontal furnace. In this study, the structures of Sm3+ or Tb3+ -doped Lu3Ga2Al3O12 phosphors were observed using an XRD (X-ray diffraction). The emission spectrum of Sm3+ -doped Lu3Ga2Al3O12 phosphor shows 550–650 nm in wavelength due to 4Gj to 6Hj. The measurement of emission spectrum of Tb3+ -doped Lu3Ga2Al3O12 phosphor was confirmed to 450 to 650 nm wavelength due to 5Dj to 7Fj. These phosphors have a sharp emission spectrum due to their physical properties of f-f transition. The Lu3Ga2Al3O12 has a high effective Z-number (Zeff = 57) which is sensitive to X-ray or γ-ray. Therefore Sm3+ or Tb3+ -doped Lu3Ga2Al3O12 phosphors can be applied for diagnostic X-ray imaging in the medical field.

The operation of THz quantum cascade laser in the region of negative differential resistance

We investigate the light-current-voltage characteristics and emission spectra of 2.3 THz quantum cascade laser operating in the negative differential resistance (NDR) region. It was shown that the formation of electric field domains (EFDs) leads to a large number of discontinuities on the current-voltage and the total optical power on current characteristics. Measurements of emission spectra at different current (before the NDR region and in the NDR region) shows that the formation of EFDs results in decrease of the output intensity, but does not influence on Fabry-Perot multi-mode structure of THz QCL. The developed theoretical model predicts the formation of EFDs in the NDR region and qualitatively explain the experimental results.

Comparison of plasma parameters and optical emission in DC, HIPIMS and hybrid DC+HIPIMS modes of magnetron sputtering

Experimental studies of the parameters of the plasma of a magnetron discharge and optical radiation from plasma in the regime of direct current (DC), high-current mode (HIPIMS), and hybrid (DC+HIPIMS) mode for a copper cathode 100 mm in diameter were carried out. The hybrid mode of operation of the magnetron sputtering system was carried out by means of a matching unit of two power supplies APEL-M-5HIPIMS and APEL-M-5PDC. The results of the experiments showed that the plasma concentration at a distance of 120 mm from the cathode has maximum values (5.6·1011 cm−3) in the HIPIMS regime at a frequency of 500 Hz. Measurement of the optical emission spectra for a copper cathode in an argon plasma showed, that at the same average discharge power (500 W), the intensity of the copper ion lines in the high-current and hybrid modes is 3 and 1.5 times, respectively, more than in the DC regime.

Short wavelength emission properties of Tm3+ and Tm3++Yb3+ doped LaAlO3 nanocrystals and polymer composites

In this work we discuss the UV-blue luminescent properties of LaAlO3 nanocrystals doped with thulium and doubly doped with thulium and ytterbium ions as well as PMMA-based composites doped with these nanocrystals. The set of nanopowders differing in activator concentration was manufactured and exposed to versatile optical characterization, covering measurements of emission and excitation spectra as well as luminescence kinetics profiles, which enabled discussion of main processes responsible for populating the excited states of thulium. Also, the up-conversion properties of Tm3++Yb3+:LaAlO3 nanocrystals were studied using an unique spectroscopic tool – hydrostatic pressure tuned semiconductor laser. All these experimental works enabled determination of the samples of optimal properties for further processing into a form of polymer composites, which have been characterized with respect of luminescent properties under direct and up-conversion excitation.

Spatial Molecular AlO Temperature Distributions in Laser-Induced Plasma

Spatially resolved, line-of-sight measurements of aluminum monoxide emission spectra in laser ablation plasma are used with Abel inversion techniques to extract radial plasma temperatures. Contour mapping of the radially deconvolved signal intensity shows a ring of AlO formation near the plasma boundary with the ambient atmosphere. Simulations of the molecular spectra were coupled with the line profile fitting routines. Temperature results are presented with simultaneous inferences from lateral, asymmetric radial, and symmetric radial AlO spectral intensity profiles. This analysis indicates that shockwave phenomena in the radial profiles, including a temperature drop behind the blast wave created during plasma initiation were measured.

Semi-blind sparse affine spectral unmixing of autofluorescence-contaminated micrographs.

Spectral unmixing methods attempt to determine the concentrations of different fluorophores present at each pixel location in an image by analyzing a set of measured emission spectra. Unmixing algorithms have shown great promise for applications where samples contain many fluorescent labels; however, existing methods perform poorly when confronted with autofluorescence-contaminated images. We propose an unmixing algorithm designed to separate fluorophores with overlapping emission spectra from contamination by autofluorescence and background fluorescence. First, we formally define a generalization of the linear mixing model, called the affine mixture model (AMM), that specifically accounts for background fluorescence. Second, we use the AMM to derive an affine nonnegative matrix factorization method for estimating fluorophore endmember spectra from reference images. Lastly, we propose a semi-blind sparse affine spectral unmixing (SSASU) algorithm that uses knowledge of the estimated endmembers to learn the autofluorescence and background fluorescence spectra on a per-image basis. When unmixing real-world spectral images contaminated by autofluorescence, SSASU greatly improved proportion indeterminacy as compared to existing methods for a given relative reconstruction error. The source code used for this paper was written in Julia and is available with the test data at https://github.com/brossetti/ssasu.

Standardization of a UV LED Peak Wavelength, Emission Spectrum, and Irradiance Measurement and Comparison Protocol.

Standard protocols for the measurement of irradiance, peak wavelength, and emission spectra have not yet been established for UV LED devices. This lack of standardization creates an uneven field for comparison between products. A detailed protocol was developed and tested in 14 facilities spanning manufacturers of UV LEDs and devices and research institutions in seven different countries. This protocol includes equipment calibration specifications, methods for the measurement and comparison calculations of irradiance and emission spectra, methods for the determination of peak wavelength, quality control and quality assurance steps, and industry-wide tolerances to error for each type of measurement. Measurements of the same source by operators using different equipment resulted in 2-10× the error found when measurement equipment provided as part of the study was used by each participant. The data were used to identify outliers, determine prediction intervals, and define acceptable tolerances to error. With this protocol, manufacturers have a means to report their UV LED specifications with verifiable quality control and quality assurance steps. The protocol and data generated from this study will create more confidence in the industry and standardize the comparison of UV LEDs by consumers, researchers, designers, and regulators.

Analysis of the Preheating Phase of Micro-Arc Discharge in Seawater, Operated Using a Needle-to-Plane Electrode with Variation in the Tip Shape

In this work, micro-arc discharge is investigated using a needle-to-plane electrode system placed with a micro-gap in highly conductive artificial seawater. A major problem with microarc discharge is the erosion of electrodes caused by the high current of the arc; however, it was found that erosion of the needle electrode did not have any effect on the discharge process in the case of precise control of the discharge gap. A simple mathematical model was developed for a more detailed study of the preheating phase of the discharge. The modeling showed good agreement with the experimental results and confirmed that the needle electrode could be reused to generate reproducible micro-arc discharges even after the erosion caused by the arc. Moreover, it was found that, in certain conditions, the preheating phase could be simulated using a simple inductor-capacitor-resistor (LCR) oscillator model with a resistor instead of electrodes immersed in the liquid. It was confirmed that the shape of the needle electrode’s tip did not affect the measurement of optical emission spectra in the case of precise focusing, which could be used in the development of compact analytical tools for on-site analysis of deep-sea water using atomic emission spectroscopy.

Microcrystalline array structures induced by heat treatment of friction-transferred organic semiconductor films

The correlation between molecular orientation and optoelectrical properties is most critical to the future design of molecular materials. We made highly-anisotropic microcrystalline array structures with an organic semiconductor, a methoxy-substituted thiophene/phenylene co-oligomer (TPCO), by depositing it on friction-transferred poly(tetrafluoroethylene) (PTFE) layers fabricated on substrates with several heat treatments. Polarising microscope observation, polarised emission and absorption spectra measurements indicated that the TPCO molecules aligned along the drawing direction of PTFE. Using these films, we fabricated two types of field-effect transistors (FETs) and compared them with those using non-heated TPCO films which provide aligned pleats structures. Ones had the channel length direction parallel to the drawing direction of PTFE and the others had the channel length direction perpendicular to that drawing direction. As for the microcrystalline array films, the mobility ratio of the former FET to that of the latter device was about 27 in the saturation region, while the emission polarisation ratio was 4.5. The heat treatment promoted the crystal growth to enhance the mobility while retaining the high anisotropy. The results demonstrate that the heat treatments of the TPCO films on the friction-transferred layers were useful for controlling crystallinity and orientation of the molecules.

Hyperfine structure measurements of neutral atomic iodine (127I) in the infrared region (1800-6000 cm−1)

Experimental measurements of high resolution emission spectra of neutral atomic iodine (I I) have been extended to cover the mid-infrared spectral regions (1800–6000 cm−1) using Fourier transform spectroscopy. A total of 354 spectral lines are reported here in the above spectral range. While the region between 3000 and 6000 cm−1 were recorded using a conventional quartz Electrodeless Discharge lamps (EDL), spectra in the region 1800–3000 cm−1 were detected using specially prepared EDLs with a CaF2 window. Hyperfine structure analysis has been carried out on 224 spectral lines, of which 176 are reported for the first time. The magnetic dipole constant (A) and electric quadrupole constant (B) have been derived for 97 energy levels.

Co-emission and energy transfer of Sm3+ and/or Eu3+ activated zinc-germanate- tellurite glass as a potential tunable orange to reddish-orange phosphor

Sm3+/Eu3+ single doped and co-doped zinc-germanate-tellurite glasses were prepared by the glass melting method. Raman and optical spectroscopic properties of Sm3+, Eu3+ and Sm3+/Eu3+ doped TeO2-GeO2-ZnO glasses have been characterized through optical absorption and pulsed/steady fluorescence. Excitation and emission spectra measurements indicated that the energy transfer process Sm → Eu is active in the samples. The concentration of europium ions was varied to provide red emission for possible control over the chromaticity tuning in the red-orange region. Upon 344 nm excitation, the color of the global emission can be adjusted from orange of 2038 K to reddish-orange of 1683 K by increasing the Eu3+ content from 1 up to 2% mol, and co-doped with 0.5% mol Sm3+. Reddish-orange color purity very close to 100% is attained when the phosphors are excited at 406 nm. The time shortening of Sm3+ emission decay in the presence of Eu3+ was attributed to a Sm3+ → Eu3+ non-radiative energy transfer process. From fitting the Sm3+ emission decay profile with the Inokuti-Hirayama model, it was inferred that the energy transfer process could be dominated by an electric dipole-dipole interaction.

Novel 1,3-bis(p-substituted phenylamino)squaraine dyes. The synthesis and spectroscopic studies

A series of new squaraine dyes was synthesized by the condensation of 1,2-dihydroxycyclobuten-3,4-dione with various p-substituted anilines. The spectroscopic properties of these compounds were studied in ten solvents exhibiting different polarity. The solvatochromism of 1,3-bis(p-substituted phenylamino)squaraines in selected solvents was studied by measurement of absorption and emission spectra, and analyzed using the empirical Kamlet-Taft solvent parameter set. New synthesized dyes absorb in the UV–Vis region with the maximum located at about 340–410 nm and display low fluorescence quantum yield about 1 × 10−3.

Extra-plastidial degradation of chlorophyll and photosystem I in tobacco leaves involving 'senescence-associated vacuoles'.

Chlorophyll (Chl) loss is the main visible symptom of senescence in leaves. The initial steps of Chl degradation operate within the chloroplast, but the observation that 'senescence-associated vacuoles' (SAVs) contain Chl raises the question of whether SAVs might also contribute to Chl breakdown. Previous confocal microscope observations (Martínez etal., 2008) showed many SAVs containing Chl. Isolated SAVs contained Chla and b (with a Chla/b ratio close to 5) and lower levels of chlorophyllidea. Pheophytina and pheophorbidea were formed after the incubation of SAVs at 30°C in darkness, suggesting the presence of Chl-degrading activities in SAVs. Chl in SAVs was bound to a number of 'green bands'. In the most abundant green band of SAVs, Western blot analysis showed the presence of photosystem I (PSI) Chl-binding proteins, including the PsaA protein of the PSI reaction center and the apoproteins of the light-harvesting complexes (Lhca1-4). This was confirmed by: (i) measurements of 77-K fluorescence emission spectra showing a single emission peak at around 730nm in SAVs; (ii) mass spectrometry of the most prominent green band with the slowest electrophoretic mobility; and (iii) immunofluorescence detection of PsaA in SAVs observed through confocal microscopy. Incubation of SAVs at 30°C in darkness caused a steady decrease in PsaA levels. Overall, these results indicate that SAVs may be involved in the degradation of PSI proteins and their associated chlorophylls during the senescence of leaves.