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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Radiation transfer in the spectra of short-pulse laser-heated targets

The conditions in laser-produced plasmas are frequently determined with x-ray spectroscopy by comparing calculated to measured spectra. Line spectra from K-shell transitions of low- to mid-atomic number elements are most often used since the important physical processes are well understood and reliable spectra can be readily measured and calculated. Radiation transfer effects due to large optical depths of strong lines can influence the spectra. In this work, the effects of radiation transfer on the emission spectra of short-laser pulse-heated targets are studied. The possible errors made in inferring electron temperature by not including radiation transfer are quantified. The inclusion of radiative transfer in spectral calculations improves the accuracy of typical temperature diagnostics and allows the use of strong lines for diagnostics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2015

Fluorine and Lithium at the Kimberley Outcrop, Gale Crater

ChemCam is an active remote sensing instrument which has operated successfully on MSL since landing in August, 2012. Its laser pulses remove dust and to profile through weathering coatings of rocks up to 7 m away. Laser-induced breakdown spectroscopy (LIBS) produces emission spectra of materials ablated from the samples in electronically excited states. As the plasma cools, elements can recombine and molecular emission lines are observed. Recent experiments have shown that some of these molecular emissions can be much brighter than the associated atomic lines, especially when halo-gens and rare earth elements are present. We observed these molecular emissions in some of the ChemCam spectra and report the first detection of chlorine and fluorine with ChemCam. It is also the first time ever that fluorine has been detected on the surface of Mars. Among all the F-bearing observations, one third are observed in the Kimberley outcrop. We will dis-cuss the potential mineralogies related to these observations as well as the related elemental correlations and propose interpretations.

Forni, O.↗
NASA NTRS1982

Middle infrared remote sensing for geology

The middle infrared portion of the spectrum available for geologic remote sensing extends from approximately 3 to 25 micrometers. The source of energy is thermal radiation from surface materials and ambient terrestrial temperatures. The spectral range of usefulness is limited by both the amount of energy available and by transmission of energy through the atmosphere. The best atmospheric window lies between about 8 and 14 micrometers. Remote sensing of the Earth in the infrared is just on the threshold of becoming a valuable geologic tool. Topics which need study include: (1) the used and limitations of the 8 to 14 micrometer region for distinguishing between silicates and nonsilicates; (2) theoretical and experimental understanding of laboratory spectra of rocks and minerals and their relationship to remotely sensed emission spectra; and (3) the possible use of the 3 to 5 and 17 to 25 micrometer portions of the spectrum for remote sensing.

Kahle, A. B.↗
NASA NTRS2000

Optical Characterization of Bulk ZnSeTe Solid Solutions

Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe and ZnSe (sub 1-x) Te (sub x) (0 less than x less than 0.4) grown by physical vapor transport technique. The energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. The best fit to the band gap vs. composition, x, data gives a bowing parameter of 1.336 which is between the value of 1.23 determined previously on ZnSeTe bulk crystals by reflectivity and the value of 1.621 reported on epilayers by photoconductivity. Low-temperature photoluminescence (PL) spectra were measured on 6 samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe (sub 1-x) Te (sub x) samples, 0.09 less than x less than 0.39. For x = 0.09, this emission energy is about 0.2eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x = 0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted to be associated with the exciton bound to Te clusters because of the high Te content in these samples.

Su, Ching-Hua↗
NASA NTRS2000

Optical Characterization of Bulk ZnSeTe Solid Solutions

Optical characterization was performed on wafers sliced from crystals of ZnSe, ZnTe, and ZnSe(1-x)Te(x)(0 less than x less than 0.4) grown by physical vapor transport. Energy band gaps at room temperature were determined from optical transmission measurements on 11 wafers. A best fit curve to the band gap versus composition x data gives a bowing parameter of 1.45. This number lies between the value of 1.23 determined previously on ZnSeTe bulk crystals and the value of 1.621 reported on ZnSeTe epilayers. Low-temperature photoluminescence (PL) spectra were measured on six samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe(1-x)Te(x) samples, 0.09 less than x less than 0.39. For x=0.09, this emission energy is about 0.2 eV lower than the band gap energy measured at low temperature. As x increases the energy discrepancy gradually decreases and reduces to almost zero at x=0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples.

Su, Ching-Hua↗
NASA NTRS2002

Crystal Growth of ZnSe and Related Ternary Compound Semiconductors by Vapor Transport

The objective of the project is to determine the relative contributions of gravity-driven fluid flows to the compositional distribution, incorporation of impurities and defects, and deviation from stoichiometry observed in the crystals grown by vapor transport as results of buoyance-driven convection and growth interface fluctuations caused by irregular fluid-flows. ZnSe and related ternary compounds, such as ZnSeS and ZnSeTe, were grown by vapor transport technique with real time in-situ non-invasive monitoring techniques. The grown crystals were characterized extensively to correlate the grown crystal properties with the growth conditions. The following are the research progress in the past two years. In-situ monitoring of partial pressure by optical absorption technique and visual observation of the growing crystal were performed during vapor growth of ZnSe. Low-temperature photoluminescence (PL) spectra and glow discharge mass spectroscopy (GDMS) were measured on ZnSe starting materials provided by various vendors and on bulk crystals grown from these starting materials by physical vapor transport (PVT) to study the effects of purification and contamination during crystal growth process. Optical characterization was performed on wafers sliced from the grown crystals of ZnSe, ZnTe and ZnSe(1-x),Te(x), (0<x<0.4). Energy band gaps at room temperature were determined from optical transmission measurements and a best fit curve to the band gap vs. composition, x, data gives a bowing parameter of 1.45. Low-temperature photoluminescence (PL) spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for the ZnSe(1-x),Te(x), samples, 0.09<x<0.39. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the exciton bound to Te clusters because of the high Te content in these samples. To validate numerical codes, in-situ monitoring during the PVT of HgI2 was designed. Optical absorption spectra of the vapor phase over HgI2 were measured for wavelengths between 200 and 600nm at sample temperatures between 349 and 610K. The Beer's Law constants for 15 wavelengths between 200 and 440 nm were determined. From these constants the vapor pressure of HgI2 was established as a function of temperature for the liquid and the solid Beta-phases To characterize the growth conditions during the PVT growth of In-doped ZnSe the optical absorbance of the vapor phase over the In-Se system were measured and were used to obtain the partial pressures of Se2(g) and In2Se(g).

Su, Ching-Hua↗
DOE OSTI2022

Long-Lived Photoluminescence of Molecular Group 14 Compounds through Thermally Activated Delayed Fluorescence

Photoluminescent molecules exploiting the sizable spin-orbit coupling constants of main group metals and metalloids to access long-lived triplet excited states are relatively rare compared to phosphorescent transition metal complexes. Here we report the synthesis of three air- and moisture-stable group 14 compounds E( Me PDP Ph ) 2 , where E = Si, Ge, or Sn and [ Me PDP Ph] 2- is the doubly deprotonated form of 2,6-bis(5- methyl-3-phenyl-1H-pyrrol-2-yl)pyridine. In solution, all three molecules exhibit exceptionally long-lived triplet excited states with lifetimes in the millisecond range and show highly efficient photoluminescence (Φ ≤ 0.49) due to competing prompt fluorescence and thermally activated delayed fluorescence at and around room temperature. Temperature-dependent steady-state emission spectra and photoluminescent lifetime measurements provided conclusive evidence for the two distinct emission pathways. Picosecond transient absorption spectroscopy allowed further analysis of the intersystem crossing (ISC) between singlet and triplet manifolds (τ ISC = 0.25-3.1 ns) and confirmed the expected trend of increased ISC rates for the heavier elements in otherwise isostructural compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dual-Emitting Cyclometalated Platinum Compounds with Isocyanide Ligands

Cyclometalated platinum(II) compounds with both C^N chelating iminic ligands and isocyanide ligands were synthesized. Two sets of compounds from the reaction of two separate HC^N ligands (derived from thiophene or benzene) with [Pt2Me4(μ-SMe 2 ) 2 ] were obtained, resulting in square planar compounds with an anionic C^N ligand, a methyl ligand, and a dimethyl sulfide (dms) ligand completing the coordination sphere. Subsequently, the dms ligand was easily substituted by several isocyanide ligands (2-naphthyl, adamantyl, 2,6-dimethylphenyl, ptoluenesulfonylmethyl). The compounds were characterized by multinuclear NMR spectroscopy, IR spectroscopy, and singlecrystal X-ray diffraction (SCXRD). Their photophysical properties were explored using UV/vis, emission, and transient absorption (TA) spectroscopy. The emission spectra for the thiophene-derived compounds showed well-defined dual emission peaks, while the benzene-derived compounds’ bands appeared less resolved. DFT and TDDFT calculations were performed, and results were compared to the observed spectroscopic properties of the newly synthesized complexes.

Inorganic carbon compounds↗
NASA NTRS1996

Radioactive Transfer Models for Saturn and Titan

The infrared spectra of the earth's atmosphere and planetary atmospheres contains information about atmospheric physical and chemical processes. Atmospheric molecular constituents absorb and emit infrared radiation by rotational and vibrational transition. Observed spectra exhibit characteristic features in the electromagnetic spectrum region. Observation of the absorption or thermal emission spectra may be obtained with space-borne high resolution infrared spectrometers in the 10-5000 cm(exp -1) (2-1000 micro-m) spectral region. Information about the atmospheric thermal structure, composition, and the chemical and physical processes of the observed spectral was accomplished. A preliminary version of a P-T retrieval algorithm for Saturn using all three modes for temperature inversion, e.g., CH4-limb, and H2-nadir spectra was completed and tested for accuracy. Radiative transfer and inversion programs were studied and analyzed for applications to infrared limb thermal emission observations of Saturn and Titan from the Cassini Orbiter, as well as Earth's atmosphere. Analysis and modification of the existing radiative transfer and inversion programs for Earth and planetary atmospheres are being made. Data analysis and retrieval of information form the observations by digital calculations were carried out at UAH and MSFC computer. The working program for generating and reading g-k arrays for using the c-k arrays via the c-k method for radiative transfer calculations for desired atmospheric and instrumental parameters was completed, tested for accuracy and resides at the MSFC computer.

Wu, S. T.↗
NASA NTRS1992

The moon - Mid-infrared (7.5- to 11.4-microns) spectroscopy of selected regions

Scaled spectral emissivity spectra have been obtained from five locations on the illuminated lunar surface and are interpreted in terms of differences in their mineralogic composition. The emission maximum, which typically falls near 8.0 microns for lunar rocks and fines, is observed to be shifted from 7.9 microns for noritic Copernicus crater walls to 8.1 microns for the olivine-rich central peak. Two mare locations show the emission maximum centered at 8.0 microns, consistent with laboratory emission measurements of basalts. An emissivity minimum at 10.5 microns in the spectrum from central peak 2 is attributed to the presence of olivine. Minima centered at 8.75 microns in the crater wall spectra resemble minima in laboratory spectra from pyroxene. A broad minimum centered at 8.5 microns in the Kepler ejecta spectrum and a sharp drop in emissivity at wavelengths longer than 11 microns in spectra from both mare locations suggest plagioclase.

Sprague, A. L.↗
DOE OSTI2024

Amplified Spontaneous Emission from Electron–Hole Quantum Droplets in Colloidal CdSe Nanoplatelets

Two-dimensional cadmium selenide nanoplatelets (NPLs) exhibit large absorption cross sections and homogeneously broadened band-edge transitions that offer utility in wide-ranging optoelectronic applications. Here, we examine the temperature-dependence of amplified spontaneous emission (ASE) in 4- and 5-monolayer thick NPLs and show that the threshold for close-packed (neat) films decreases with decreasing temperature by a factor of 2-10 relative to ambient temperature owing to extrinsic (trapping) and intrinsic (phonon-derived line width) factors. Interestingly, for pump intensities that exceed the ASE threshold, we find development of intense emission to lower energy in particular provided that the film temperature is <= 200 K. For NPLs diluted in an inert polymer, both biexcitonic ASE and low-energy emission are suppressed, suggesting that described neat-film observables rely upon high chromophore density and rapid, collective processes. Transient emission spectra reveal ultrafast red-shifting with the time of the lower energy emission. Taken together, these findings indicate a previously unreported process of amplified stimulated emission from polyexciton states that is consistent with quantum droplets and constitutes a form of exciton condensate. For studied samples, quantum droplets form provided that roughly 17 meV or less of thermal energy is available, which we hypothesize relates to polyexciton binding energy. Polyexciton ASE can produce pump-fluence-tunable red-shifted ASE even 120 meV lower in energy than biexciton ASE. Finally, our findings convey the importance of biexciton and polyexciton populations in nanoplatelets and show that quantum droplets can exhibit light amplification at significantly lower photon energies than biexcitonic ASE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2012

Spectroscopic Chemical Analysis Methods and Apparatus

This invention relates to non-contact spectroscopic methods and apparatus for performing chemical analysis and the ideal wavelengths and sources needed for this analysis. It employs deep ultraviolet (200- to 300-nm spectral range) electron-beam-pumped wide bandgap semiconductor lasers, incoherent wide bandgap semiconductor lightemitting devices, and hollow cathode metal ion lasers. Three achieved goals for this innovation are to reduce the size (under 20 L), reduce the weight [under 100 lb (.45 kg)], and reduce the power consumption (under 100 W). This method can be used in microscope or macroscope to provide measurement of Raman and/or native fluorescence emission spectra either by point-by-point measurement, or by global imaging of emissions within specific ultraviolet spectral bands. In other embodiments, the method can be used in analytical instruments such as capillary electrophoresis, capillary electro-chromatography, high-performance liquid chromatography, flow cytometry, and related instruments for detection and identification of unknown analytes using a combination of native fluorescence and/or Raman spectroscopic methods. This design provides an electron-beampumped semiconductor radiation-producing method, or source, that can emit at a wavelength (or wavelengths) below 300 nm, e.g. in the deep ultraviolet between about 200 and 300 nm, and more preferably less than 260 nm. In some variations, the method is to produce incoherent radiation, while in other implementations it produces laser radiation. In some variations, this object is achieved by using an AlGaN emission medium, while in other implementations a diamond emission medium may be used. This instrument irradiates a sample with deep UV radiation, and then uses an improved filter for separating wavelengths to be detected. This provides a multi-stage analysis of the sample. To avoid the difficulties related to producing deep UV semiconductor sources, a pumping approach has been developed that uses ballistic electron beam injection directly into the active region of a wide bandgap semiconductor material.

Hug, William F.↗
NASA NTRS2011

X-Ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-Ray Observations

We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of ionization parameter, solar iron abundance and photon index for the illuminating spectrum. These models also include the most complete and recent atomic data for the inner-shell of the iron and oxygen isonuclear sequences. We concentrate our analysis to the 2 - 10 keV energy region, and in particular to the iron K-shell emission lines. We show the dependency of the equivalent width (EW) of the Fe Ka with the ionization parameter. The maximum value of the EW is approx. 800 eV for models with log Epsilon approx. 1.5, and decreases monotonically as Epsilon increases. For lower values of Epsilon the Fe K(alpha) EW decreases to a minimum near log Epsilon approx. 0.8. We produce simulated CCD observations based on our reflection models. For low ionized, reflection dominated cases, the 2 -10 keV energy region shows a very broad, curving continuum that cannot be represented by a simple power-law. We show that in addition to the Fe K-shell emission, there are other prominent features such as the Si and S L(alpha) lines, a blend of Ar VIII-XI lines, and the Ca x K(alpha) line. In some cases the S xv blends with the He-like Si RRC producing a broad feature that cannot be reproduced by a simple Gaussian profile. This could be used as a signature of reflection.

Garcia, J.↗
NASA NTRS1994

Infrared Emissions from Shock Heated Hydrocarbons

The primary objective of this study was to ascertain whether low molecular weight hydrocarbons (LMWH) in the range C4 to C7, upon heating to temperatures above 900 K, emit IR radiations at frequencies that correspond to the 'unidentified infrared' (UIR) features - the recorded emissions from a variety of astronomical sources - reflection nebulae, HII regions, planetary nebulae, spiral galaxies and other extra galactic objects. We describe IR emission spectra recorded from shock-heated gases (C2H2; (H3C)2C = CH2; H2C = C(CH3) - C(CH3) = CH2; (H3C)2C = CH - C(CH3) = CH2), that arise from excitation of the fundamental C-H stretching vibrations. While the IR emissions from LMWH, anticipated over the entire spectra range, do not present a perfect match to UIR, the correspondence over several wavelength regions is better than the emissions anticipated from polycyclic aromatic hydrocarbon (PAH) species. Finally, we briefly review the range of proposals that have been presented for the origin of the UIR bands.

Stephens, K. M.↗
DOE OSTI2021

Modeling the infrared cascade spectra of small PAHs: the 11.2 μm band

The profile of the 11.2 μm feature of the infrared (IR) cascade emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules is investigated using a vibrational anharmonic method. Several factors are found to affect the profile including: the energy of the initially absorbed ultraviolet (UV) photon, the density of vibrational states, the anharmonic nature of the vibrational modes, the relative intensities of the vibrational modes, the rotational temperature of the molecule, and blending with nearby features. Each of these factors is explored independently and influence either the red or blue wing of the 11.2 μm feature. The majority impact solely the red wing, with the only factor altering the blue wing being the rotational temperature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Frequency-Domain Spectroscopic Study of the Photosystem I Supercomplexes, Isolated IsiA Monomers, and the Intact IsiA Ring

The PSI 3 -IsiA 18 supercomplex is one of the largest and most complicated assemblies in photosynthesis. The IsiA ring, composed of 18 IsiA monomers (IsiA 18 ) surrounding the PSI trimer (PSI 3 ), forms under iron-deficient condition in cyanobacteria and acts as a peripheral antenna. Based on the supercomplex structure recently determined via cryo-EM imaging, we model various optical spectra of the IsiA monomers and IsiA 18 ring. Comparison of the absorption and emission spectra of the isolated IsiA monomers and the full ring reveals that about 2.7 chlorophylls (Chls) are lost in the isolated IsiA monomers. The best fits for isolated monomers spectra are obtained assuming the absence of Chl 508, Chl 517 and 70% loss of Chl 511. The best model describing all three hexamers and the entire ring suggests that the lowest energy pigments are Chls 511, 514 and 517. Based on the modeling results presented in this work we conclude that there are most likely three entry points for EET from the IsiA6 hexamer to the PSI core monomer, with two of these entry points likely being located next to each other (i.e. nine entry points from IsiA 18 to the PSI 3 trimer). Lastly, we show that excitation energy transfer inside individual monomers is fast (< 2 ps at T = 5 K) and at least 20 times faster than inter-monomer energy transfer.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Line identification of boron and nitrogen emissions in EUV and VUV wavelength ranges in the impurity powder dropping experiments of LHD and its application to spectroscopic diagnostics

An impurity powder dropper was installed in the 21st campaign of the Large Helical Device experiment (Oct. 2019–Feb. 2020) under a collaboration between the National Institute for Fusion Science and the Princeton Plasma Physics Laboratory for the purposes of real-time wall conditioning and edge plasma control. In order to assess the effective injection of the impurity powders, spectroscopic diagnostics were applied to observe line emission from the injected impurity. Therefore, extreme-ultraviolet (EUV) and vacuum-ultraviolet (VUV) emission spectra were analyzed to summarize observable impurity lines with B and BN powder injection. Emission lines released from B and N ions were identified in the EUV wavelength range of 5–300 Å measured using two grazing incidence flat-field EUV spectrometers and in the VUV wavelength range of 300–2400 Å measured using three normal incidence 20 cm VUV spectrometers. BI–BV and NIII–NVII emission lines were identified in the discharges with the B and BN powder injection, respectively. Useful B and N emission lines which have large intensities and are isolated from other lines were successfully identified as follows: BI (1825.89, 1826.40) Å (blended), BII 1362.46 Å, BIII (677.00, 677.14, 677.16) Å (blended), BIV 60.31 Å, BV 48.59 Å, NIII (989.79, 991.51, 991.58) Å (blended), NIV 765.15 Å, NV (209.27, 209.31) Å (blended), NVI 1896.80 Å, and NVII 24.78 Å. Applications of the line identifications to the advanced spectroscopic diagnostics were demonstrated, such as the vertical profile measurements for the BV and NVII lines using a space-resolved EUV spectrometer and the ion temperature measurement for the BII line using a normal incidence 3 m VUV spectrometer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗