Search NASA⌕ Search

SEARCH · Search NASA

Results for “Optical Absorption”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Au 130− x Ag x Nanoclusters with Non‐Metallicity: A Drum of Silver‐Rich Sites Enclosed in a Marks‐Decahedral Cage of Gold‐Rich Sites

Abstract The synthesis and structure of atomically precise Au 130− x Ag x (average x= 98) alloy nanoclusters protected by 55 ligands of 4‐ tert ‐butylbenzenethiolate are reported. This large alloy structure has a decahedral M 54 (M=Au/Ag) core. The Au atoms are localized in the truncated Marks decahedron. In the core, a drum of Ag‐rich sites is found, which is enclosed by a Marks decahedral cage of Au‐rich sites. The surface is exclusively Ag−SR; X‐ray absorption fine structure analysis supports the absence of Au−S bonds. The optical absorption spectrum shows a strong peak at 523 nm, seemingly a plasmon peak, but fs spectroscopic analysis indicates its non‐plasmon nature. The non‐metallicity of the Au 130− x Ag x nanocluster has set up a benchmark to study the transition to metallic state in the size evolution of bimetallic nanoclusters. The localized Au/Ag binary architecture in such a large alloy nanocluster provides atomic‐level insights into the Au−Ag bonds in bimetallic nanoclusters.

Higaki, Tatsuya↗
DOE OSTI2019

Gold nanoparticles in reverse micellar solutions: preparation, optical properties, and dimensional characteristics

Gold nanoparticles (NPs) were synthesized via chemical (Chem) and radiation-chemical (RadChem) methods for the reduction of ions in reverse micellar solutions (RMS). The gold NP have for the first time been obtained by self-organization (Self-assembly), and their optical properties were evaluated. The formation of Au NP (Chem, RadChem, and Self) was confirmed by the transmission electron microscopy. The spectral characteristics of optical absorption of gold NP in the RMS depend on the solubilization coefficient ω, the salt concentration, and the methods for initiating the primary steps of reduction reactions responsible for the formation of nanoscale structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Room temperature novel chemical synthesis of Cu{sub 2}ZnSnS{sub 4} (CZTS) absorbing layer for photovoltaic application

Highlights: Black-Right-Pointing-Pointer Simple and inexpensive method for the synthesis of CZTS films. Black-Right-Pointing-Pointer Structural, morphological and optical properties. Black-Right-Pointing-Pointer Find great application in solar cells with efficiency 0.12%. -- Abstract: Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films have been prepared by a novel chemical successive ionic layer adsorption and reaction (SILAR) method. These films were annealed in vacuum at 673 K and further characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy, electrical, and wettability studies. The X-ray diffraction studies showed the formation of kesterite structure of CZTS films. Scanning electron micrograph revealed the formation of densely packed, compact and large grained CZTS films. The CZTS films showed high optical absorption (10{sup 4} cm{sup -1}) exhibiting band gap energy of 1.55 eV. Wettability test revealed the hydrophilic nature of CZTS films. The CZTS thin films showed semiconducting behavior with p-type electrical conductivity. Further photovoltaic activity of these films was studied by forming the photoelectrochemical cell.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effects of zinc salts on the structural and optical properties of acidic chemical bath deposited ZnS thin films

Graphical abstract: XRD patterns of annealed ZnS films from different zinc salts. Curves a, b, c, d correspond to the annealed ZnS–C1, ZnS–S{sub 3}, ZnS–Cl{sub 2}, ZnS–N{sub 2} thin films. Display Omitted Highlights: ► ZnS thin films were deposited using different zinc salts. ► The grain sizes of deposited ZnS thin films are about 12.5 15.5 nm. ► The band gaps of deposited ZnS thin films were in the range of 3.66–3.83 eV. -- Abstract: ZnS thin films were deposited from different zinc salts by chemical bath deposition (CBD). Structural, morphological and optical characterizations were performed using different methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectra. The particle sizes of as-deposited ZnS thin films were calculated to be about 12.5–15.5 nm and the crystal qualities were improved after annealed at 500 °C in Ar/H{sub 2}S (5%) atmosphere. Optical absorption measurements indicated that the band gaps of ZnS thin films were in the range of 3.66–3.83 eV and they decreased with the increasing of particle sizes. ZnCl{sub 2} was found to the best precursor due to the higher crystal quality and compact surface of deposited ZnS thin films.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of X-Ray Radiation on the Optical Properties of Photorefractive Bismuth-Silicate Crystals

The results of investigations of the optical-absorption spectra of bismuth-silicate (Bi{sub 12}SiO{sub 20}) single crystals are presented. The band-gap width and the characteristic Urbach energy are determined. The effect of preliminary X-ray irradiation on the behavior of the experimental spectral dependences and the values of the characteristic parameters induced by the bismuth-silicate defect structure is established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Dynamics of Photocatalytic Hydrogen Production in Aqueous Dispersions of Monolayer-Rich Tungsten Disulfide

Two-dimensional tungsten disulfide (WS 2 ) is an emerging semiconducting photocatalyst featuring high optical absorption, carrier mobility, and catalytic activity toward hydrogen evolution. While characterization of its optical and electrocatalytic properties has advanced, less is known about its ultrafast carrier dynamics and intrinsic photocatalytic activity in aqueous systems producing hydrogen. This work removed extraneous variables often found in photoelectrochemical systems, thereby allowing the intrinsic proton reduction rate for monolayer-rich WS2 nanosheets to be estimated via transient absorption lifetimes and a developed kinetic scheme. Addition of a hole scavenger, ascorbic acid (AA), resulted in a 3-fold increase in carrier lifetimes following photoexcitation. Longer electron lifetimes with AA yielded a 14-fold increase in hydrogen production. An intrinsic proton reduction rate constant was extracted that may be extended to any photoelectrochemical or electrochemical hydrogen evolution scheme involving small, monolayer-rich WS 2 catalysts. This represents an important step in better understanding catalytic systems utilizing TMD catalysts.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Theoretical investigation of stabilities and optical properties of Si{sub 12}C{sub 12} clusters

By sorting through hundreds of globally stable Si{sub 12}C{sub 12} isomers using a potential surface search and using simulated annealing, we have identified low-energy structures. Unlike isomers knit together by Si–C bonds, the lowest energy isomers have segregated carbon and silicon regions that maximize stronger C–C bonding. Positing that charge separation between the carbon and silicon regions would produce interesting optical absorption in these cluster molecules, we used time-dependent density functional theory to compare the calculated optical properties of four isomers representing structural classes having different types of silicon and carbon segregation regions. Absorptions involving charge transfer between segregated carbon and silicon regions produce lower excitation energies than do structures having alternating Si–C bonding for which frontier orbital charge transfer is exclusively from separated carbon atoms to silicon atoms. The most stable Si{sub 12}C{sub 12} isomer at temperatures below 1100 K is unique as regards its high symmetry and large optical oscillator strength in the visible blue. Its high-energy and low-energy visible transitions (1.15 eV and 2.56 eV) are nearly pure one-electron silicon-to-carbon transitions, while an intermediate energy transition (1.28 eV) is a nearly pure carbon-to-silicon one-electron charge transfer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Optical nanostructures design, fabrication, and applications for solar/thermal energy conversion

Optical nanostructures can control the optical absorption and emission properties of surfaces and are therefore being investigated for solar thermophotovoltaics, thermophotovoltaics, solar thermal, infrared sensing, infrared sources, incandescent light sources, and thermal imaging applications, among many others. This review article describes various modeling methods available for design of optical nanostructures to control light absorption and emission properties of surfaces, as well as various methods available for the fabrication of large area nanostructured surfaces. Throughout the review, we provide examples of state of the art energy generation devices using such optical nanostructures. A discussion of outstanding obstacles for the achievement of high efficiency solar thermophotovoltaics systems is provided along with examples of systems showing exceptional promise.

Gupta, Mool C.↗
DOE OSTI2018

Novel preparation of an ancient ceramic pigment BaCuSi4O10 and its performance investigation

Highlights: • The BaCuSi{sub 4}O{sub 10} (Chinese blue) was prepared firstly by coprecipitation and hydrothermal process at 180 °C for 20 h, and then sintered at 800 °C, resulting in pigment with superior performance. • The as-prepared pigment possesses bright blue coloration, preferable flower-like mesoporous microspheres morphology and qualified purity. • This novel process could fabricate the BaCuSi{sub 4}O{sub 10} pigment with broadband optical absorption and better emission in the near-infrared region. • This novel process decreases the calcination temperature compared with the traditional solid state method and also lowers the hydrothermal temperature and time compared with only a sole hydrothermal process. - Abstract: The BaCuSi{sub 4}O{sub 10} (Chinese blue) was prepared by coprecipitation and hydrothermal process at 180 °C for 20 h prior to sintering at 800 °C with a final pigment of superior performance. The crystalline configuration and microstructure of the product were characterized by XRD, FTIR, SEM and TEM. The electronic structure and the valence situation were determined by XPS. The coloration was studied with colorimeter. The absorption and the luminescence properties were examined with an UV−VIS-NIR spectrometer and a spectrofluorimeter, respectively. The results show that the BaCuSi{sub 4}O{sub 10} pigment prepared by this combined fabrication process possesses flower-like mesoporous microspheres morphology, better crystallization, clear coloration and rather qualified purity. The as-prepared BaCuSi{sub 4}O{sub 10} pigment also shows well optical property with broadband absorption and better emission in the 800–1200 nm range. Compared with traditional solid state fabrication or only sole hydrothermal process, this novel process can also reduce hydrothermal temperature and time, and decrease calcination temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Continuum laser absorption spectroscopy of C 2 (a 3 Π u ) in a sublimating cloud of carbon black

A direct optical absorption diagnostic has been developed for rotationally resolved measurements of diatomic carbon (a 3 Π u →d 3 Π g (0,0) and (1,1)) at a repetition rate of 525 kHz and resolution of 7.3 pm over the range of 511.1–514.1 nm. The diagnostic utilizes a high-power pulsed continuum laser light source dispersed in a spectrograph and imaged by a high-speed camera. Measurements have been performed that capture the temporal evolution of C 2 number density and temperature of a cloud of carbon black sublimating in shock heated gas at high temperature and pressure (T = 5500 K, P = 3.7 atm). A simultaneous light absorption measurement of the condensed phase enables comparisons of the gaseous C 2 number density to the condensed phase mass. The continuum laser absorption diagnostic is applied to C 2 in this work but shows promise in being a simple “drop-in” system for absorption spectroscopy in the visible range at rapid repetition rates and high dispersion, filling an important gap for laser diagnostic systems.

Willhardt, Colton Dean [Univ. of Illinois at Urban↗
DOE OSTI2018

Absorption of Far-Infrared Radiation in Ge/Si Quantum Dots

The experimental and theoretical results of studies of optical absorption in doped Ge/Si quantumdot structures in the far-infrared region, corresponding to the energies of transitions of holes from the ground state to the lowest excited size-quantization state, are reported. An analytical theory of the size quantization of holes in a lens-shaped quantum dot is developed in the context of the adiabatic approximation with consideration for pair Coulomb interaction. It is shown that the interaction has no effect on the frequencies of lower interlevel resonances. This fact is representative of generalized Kohn’s theorem satisfied due to the specific geometric shape of the quantum dot. The experimental and theoretical values of the transition energies are in good agreement.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dual-Color Optical Recording of Bioelectric Potentials by Polymer Electrochromism

Optical recording based on voltage-sensitive fluorescent reporters allows for spatial flexibility of measuring from desired cells, but photobleaching and phototoxicity of the fluorescent labels often limit their sensitivity and recording duration. Voltage-dependent optical absorption, rather than fluorescence, of electrochromic materials, would overcome these limitations to achieve long-term optical recording of bioelectrical signals. Electrochromic materials such as PEDOT:PSS possess the property that an applied voltage can either increase or decrease the light absorption depending on the wavelength. In this work, we harness this anticorrelated light absorption at two different wavelengths to significantly improve the signal detection. With dual-color detection, electrical activity from cells produces signals of opposite polarity, while artifacts, mechanical motions, and technical noises are uncorrelated or positively correlated. Using this technique, we are able to optically record cardiac action potentials with a high signal-to-noise ratio, 10 kHz sampling rate, >15 min recording duration, and no time-dependent degradation of the signal. Furthermore, we can reliably perform multiple recording sessions from the same culture for over 25 days.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Ab initiomany-body Green's function calculations of optical properties of LiF at high pressures

We present density functional theory (DFT) + quasiparticle self-energy (G 0 W 0 )+ Bethe-Salpeter calculations of the real and imaginary parts of the long-wavelength dielectric function of LiF between ambient pressure and P=5 Mbars. While the optical absorption spectrum is predicted to show dramatic pressure-dependent features above the optical gap, the index of refraction well below the gap is shown to exhibit the same trends as that seen in both DFT calculations and experiment: a roughly linear increase with density. This increase does not result from a decrease in the band gap, but rather follows from the increase in oscillator strength which counteracts a smaller increase in band gap with P. Our calculations also suggest that the index of refraction (for visible and near-UV light) of the higher-T B 2 phase should be quite close to that of the B 1 (ambient crystalline) phase. These findings may be of interest to researchers who use LiF as a window material in dynamic compression experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Bending effects and optical properties of WSe 2 nanoribbons of topological phase

A WSe 2 monolayer of 1T' phase is a large band gap quantum spin Hall insulator, supporting dissipationless charge and spin transports through the topologically protected edge states. Here, in this work, we explore the nanoribbon forms of 1T' phase WSe 2 by first-principles density functional calculations and the many-body perturbation GW and Bethe-Salpeter equation method. We found that the 1T' WSe 2 nanoribbon can show topological edge states with a ribbon width of ~4-6 nm. Those edge bands show crossing through the Fermi level an odd number of times, with one kind of spin-polarization connecting the valence band continuum and conduction band continuum. The topological features of the edge bands hold even under small and medium bending in the nanoribbon, while large bending induces large band splitting, resulting in a topological switch-off in the edge bands. The semiconducting 1T' WSe2 nanoribbon shows a large tunability with bending in optical absorption spectra and exciton states. The lowest-energy exciton is changed from optically dark in the flat nanoribbon to bright in the bent nanoribbons. These properties in the 1T' WSe 2 nanoribbons suggest potential applications in controllable quantum electronics and exciton-based quantum information processes.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of silver doping on ZnO nanocrystals

Ag doped ZnO nanocrystals were synthesized by co-precipitation method with the nominal compositions (x=0.00, 0.02, 0.04, 0.06). The as-synthesized Ag doped ZnO nanocrystals were characterized by X-ray diffraction (XRD), FTIR and UV-Vis. From XRD patterns samples shows hexagonal structure. The average crystallite size is in the range of 41-47 nm. All as synthesized Zn{sub 1−x}Ag{sub x}O nanocrystals are highly textured, with wurtzite structure along the (101) growth direction. The energy band gap of pure and Ag doped ZnO were calculated from UV-Vis spectra. FTIR spectra were confirmed that Ag substituted into ZnO. Chemical species of the samples were detected using FTIR spectra An increase in the hexagonal lattice parameters of ZnO is observed on increasing the Ag concentration. An optical absorption study shows an increment in the band gap with increasing Ag content. From optical study the samples determines blue shift. Atomic packing fraction (APF) and c/a ratio were calculated using XRD data. It confirms the formation of ZnO with the stretching vibrational mode around at 506 to 510 cm{sup −1}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

A facile synthesis of metal nanoparticle - graphene composites for better absorption of solar radiation

Herein, a facile chemical approach has been adopted to prepare silver nanoparticles (AgNPs)- graphene (G) composite to study photothermal effect. Sodium borohydride (SBH), a strong reducing agent has been selected for this work. Effect of SBH concentrations on optical behavior of AgNPs-G composite was also investigated. Resultant materials were characterized by various techniques including X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), optical absorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM micrographs confirm wrapping of AgNPs into graphene whereas XRD analysis reveals their particle size variation between 47 nm to 69 nm. Optical studies throw a light on their strong absorption behavior towards solar radiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Optical constants, single-oscillator modal and refractive index dispersion analysis of lithium zinc bismuth borate glasses doped with Eu{sup 3+} ions

The glasses of composition xLi{sub 2}O-15ZnO- 20Bi{sub 2}O{sub 3}- (64 - x) B{sub 2}O{sub 3}- 1EuO (ZLB) (where x=0, 5, 10, 15, 20 mole %) prepared by melt-quenching technique. The amorphous nature of the prepared glasses was confirmed by XRD spectra. The UV-Vis optical absorption spectrum was recorded in the wave length range of 200-1000 nm. It is observed that the optical band gap is inversely changing with Urbach energy. The optical constants such as G (a constant proportional to the second-order deformation potential) and E{sub f} (a constant that depends on local coordination and is called as free energy of the glass system). The most significant result of the present work is the refractive index dispersion curves of the ZLB glasses obey the single-oscillator model and oscillator parameters (E{sub o}, E{sub d}) changed with the Li{sub 2}O content. the absorption edge, band gap and Urbach energy is changing nonlinearly with increasing content of Li{sub 2}O, which can be used to calculate the optical, physical, and other constants.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Spontaneous Formation of Single-Crystalline Spherulites in a Chiral 2D Hybrid Perovskite

In two-dimensional (2D) chiral metal-halide perovskites (MHPs), chiral organic spacers induce structural chirality and chiroptical properties in the metal-halide sublattice. This structural chirality enables reversible crystalline-glass phase transitions in (S-NEA) 2 PbBr 4 , a prototypical chiral 2D MHP where NEA + represents 1-(1-naphthyl)ethylammonium. Here, in this study, we investigate two distinct spherulite states of (S-NEA) 2 PbBr 4 , exhibiting either radial-like or stripe-like banded patterns depending on the annealing conditions of the amorphous film. Despite similarities in optical absorption and photoluminescence, the stripe-like, banded spherulite exhibits higher crystallinity and improved optical transparency compared to those of radial-like spherulite. X-ray nanoprobe measurements reveal tilting-angle modulations in the octahedral plane of stripe-like spherulites, correlating with the film’s surface geometry. Transfer matrix calculations indicate that the optical contrast in stripe-like patterns, seen in bright-field optical microscopy, arises from optical interference effects, differing from the contrast mechanism observed in polymer spherulites. Ultrafast carrier dynamics experiments suggest that the stripe-like spherulites resemble single crystals more closely than radial-like spherulites, while electrical conductivity measurements show enhanced charge carrier transport in stripe-like spherulites. These findings offer insights into MHP spherulite states with a single composition but different morphologies, previously observed only in polymers, highlighting their potential for optoelectronic applications.

36 MATERIALS SCIENCE↗