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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.

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At least 1,135 records · Page 63
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Insight into the Structural and Emissive Behavior of a Three‐Dimensional Americium(III) Formate Coordination Polymer

Abstract We report the structural, vibrational, and optical properties of americium formate (Am(CHO 2 ) 3 ) crystals synthesized via the in situ hydrolysis of dimethylformamide (DMF). The coordination polymer features Am 3+ ions linked by formate ligands into a three‐dimensional network that is isomorphous to several lanthanide analogs, (e. g., Eu 3+ , Nd 3+ , Tb 3+ ). Structure determination revealed a nine‐coordinate Am 3+ metal center that features a unique local C 3v symmetry. The metal–ligand bonding interactions were investigated by vibrational spectroscopy, natural localized molecular orbital calculations, and the quantum theory of atoms in molecules. The results paint a predominantly ionic bond picture and suggest the metal‐oxygen bonds increase in strength from Nd−O 5 D 1′ → 7 F 0′ emission band is observed and dominates the emission spectrum. This behavior is unusual and is attributed to the C 3v coordination environment of the metal center.

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

How Should Researchers Measure Perovskite-Based Monolithic Multijunction Solar Cells’ Performance? A Calibration Lab's Perspective

Perovskite multijunctions (PVSK MJs) have made remarkable progress with monolithic PVSK/PVSK tandems surpassing the efficiency of single-junction (1 J) PVSK cells and PVSK/Si cells reported to exceed the 30% efficiency mark. These efficiencies are reported at standard test conditions (STC), established by the photovoltaic (PV) community to facilitate comparison between devices and technologies. Herein, it is discussed why an accurate STC performance measurement for a MJ is more complicated than for a 1 J cell and the special aspects to be considered when measuring the current-voltage characteristics and the performance of PVSK-containing MJ cells are emphasized. It is discussed why a spectrally adjustable solar simulator is needed and the sequence of accurate performance measurement, namely measurement of the spectral response of each junction, adjustment of the spectrum, and appropriate protocols for measuring the power output of the device at STC, is presented. For all these, common errors and pitfalls that sometime lead to misleading interpretation of the results are presented, and the methods to evaluate the accuracy of the data when a spectrally adjustable solar simulator is not available are recommended. Finally, first step is taken toward recommending performance measurement approaches when high throughput is required as will eventually be in a production line.

14 SOLAR ENERGY↗
DOE OSTI2025

Remote quantification of Cm(III) and HNO 3 by fluorescence spectroscopy and chemometrics

A unique approach to remotely quantify Cm(III) (0–100 µg mL −1 ) in HNO 3 (1–12 M) using steady-state laser fluorescence spectroscopy and multivariate regression models was developed. Photoluminescence is amenable to remote measurements using fiber-optic cables and is sensitive to numerous lanthanide and actinide species. In-line measurements can provide feedback to support complex processing in harsh environments (e.g., hot cells) to help guide and optimize radiochemical separations. In this work, Cm(III) spectra were acquired remotely in a glove box as a function of HNO 3 concentration to better understand spectral characteristics and evaluate the utility of multivariate regression models in this system. Furthermore, the Cm(III) fluorescence peak shape, width, position, and intensity changed significantly as a function of HNO 3 concentration, likely because of the displacement of emission quenching inner-sphere water molecules and complexation with nitrate ions. Despite significant covariance and nonlinearity in the data, a D-optimal design strategy successfully minimized training set sample size and was used to build effective partial least squares regression models for Cm(III) and HNO 3 concentrations without a priori knowledge of solution conditions. Chemometrics for modeling complex fluorescence spectra are promising and may find widespread applicability for online analysis in numerous chemical systems found in the nuclear field.

Actinide↗
DOE OSTI2021

Pyrene-fused hexaarylbenzene luminogens: Synthesis, characterization, and aggregation-induced emission enhancement

Six novel pyrene-fused hexaarylbenzene derivatives (3a-f) were designed, synthesized, and characterized, which exhibited aggregation-induced emission enhancement (AIEE) in the aggregated state by means of THF/H 2 O mixtures. Techniques such as theoretical calculations, single crystal X-ray diffraction, and photophysical measurements in solution and in the solid state were employed to illustrate the tunable, variable, and sensitive AIEE features in this system. Both theoretical and experimental results revealed that the nature of the multiple photoluminescence should be taken into account when elucidating and designing the multiple photoluminescence phenomenon and molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Thermal Processing Conditions for the Synthesis of Near Theoretical Density Li 5 La 3 Ta 2 O 12 Ceramics for Ceramic Dual-Mode Detectors

A family of Li-containing garnet compounds, extensively investigated for Li-ion solid electrolyte applications, show great potential to be developed into transparent ceramic dual-mode scintillators. In particular, Li 5 La 3 Ta 2 O 12 (LLTaO) shows promise as an efficient dual-mode scintillator due to its high Li content, high density, non-hygroscopicity, and high effective-Z. Often the synthesis of LLTaO ceramics involves solid state processing techniques starting with oxide and carbonate powders, calcining, sintering for the removal of residual porosity, and post-processing. This study focuses on two objectives: (1) establishing thermal processing boundary conditions for a flexible alkoxide-based sol-gel method for synthesizing fine-grained powders; and (2), consolidating powders via hot-pressing to form high-density ceramics. In this study, near single-phase ceramics were achieved by hot-pressing sol-gel powders with varying amounts of excess Li. Rietveld refinements were used to analyze X-ray diffraction data and provide a quantitative evaluation of the phases present in the hot pressed ceramics. Some of the diffraction data showed large low angle peak asymmetry, suggesting the presence of two cubic Li 5 La 3 Ta 2 O 12 garnet phases with different lattice parameters. Depending on the synthesis and processing conditions, the refinement revealed ~ 90 wt% concentration of a phase with a ≈ 12.8 Å and ~ 10 wt% concentration of a phase with a ≈ 12.9 Å, indicating a remaining excess of Li in the hot pressed ceramics in the large lattice parameter phase. These synthesis experiments allowed for the determination of a baseline for Li loss during hot-pressing. X-ray excited radioluminescence and photoluminescence excitation and emission spectra were obtained from the hot pressed ceramics. In conclusion, the measured emission spectra featured broad tantalate emission and line emissions likely from a rare-earth impurity.

36 MATERIALS SCIENCE↗
DOE OSTI2021

On optical properties and scintillation performance of emerging Ga 2 O 3 : Crystal growth, emission mechanisms and doping strategies

As an emerging ultra-wide bandgap compound semiconductor, Ga 2 O 3 has attracted rapidly growing interest due to its unique physical properties for harsh condition applications. Compared to Ga 2 O 3 ’s electrical-characteristic based uses, such as power electronics, photodetectors and solar cells, a much less explored area for Ga 2 O 3 is its promising optical properties and its related scintillation capabilities. Undoped Ga 2 O 3 is a strong scintillator with excellent scintillation characteristics such as fast decay constants and encouraging light yield which is comparable to that of the classic Bi 4 Ge 3 O 12 (BGO) scintillator. The scintillation capability of Ga 2 O 3 can be precisely tuned via a series of approaches including systematic crystal growth control, post-growth annealing, targeted doping, and optimization of operation temperature. Here we summarize exciting progress of Ga 2 O 3 scintillators which have been pursued over the past few years. Our efforts cover a series of growth techniques of Ga 2 O 3 materials as well as discussion of emission mechanisms. Here we dedicate a targeted portion toward the doping strategies to improve the performance of Ga 2 O 3 . A detailed analysis is provided to compare the impact of different dopants. Through these efforts, we hope to provide useful perspectives to help accelerate the development of high performance Ga 2 O 3 scintillators.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Scintillating crystals for the Neutral Particle Spectrometer in Hall C at JLab

This report discusses the quality and performance of currently available PbWO crystals of relevance to high-resolution electromagnetic calorimetry, e.g. detectors for the Neutral Particle Spectrometer at Jefferson Lab or those planned for the Electron–Ion Collider. Since the construction of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) and early PANDA (The antiProton ANnihilations at DArmstadt) electromagnetic calorimeter (ECAL) the worldwide availability of high quality PbWO 4 production has changed dramatically. We report on our studies of crystal samples from SICCAS/China and CRYTUR/Czech Republic that were produced between 2014 and 2019.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

The power of lanthanides: same composition, but different lanthanides leading to different interesting materials properties, from magnetocalorics to molecular magnets and phosphors

Commonly accepted design concepts for ionic liquids (ILs) state that the constituting ions must be large and carry low, well-dispersed charges. A series of ILs based of pentadeca charged ILs with pentanuclear linear {Ln 5 } units ([Ln 5 (C 2 H 5 -C 3 H 3 N 2 -CH 2 COO) 16 (H 2 O) 8 ](Tf 2 N) 15 (C 3 H 3 N 2 = imidazolium moiety, Tf 2 N = bis(trifluoromethanesulfonyl)amide) with Ln = Er, Ho, Tm) demonstrates that these criteria are not absolute. Highly charged ions can also support IL formation, provided they are sufficiently large. Expanding the series of these unconventional, record pentadeca charged with new lanthanide representatives, led to the discovery of additional unprecedented properties for ILs: The Gd compound exhibits a strong magnetocaloric effect (MCE) in the liquid state with a maximum magnetic entropy change of −ΔS M = −11 J⋅kg −1 ⋅K −1 at 2 K for Δμ 0 H = 7 T. Albeit the Dy representative shows slow magnetic relaxation, the relaxation times are not favorable for practical application as a molecular magnet. Lastly, for both the Gd and the Y compound, phosphorescence in the seconds time scale is observed, which is, to the best of our knowledge, the longest ever reported for an IL.

Ionic Liquids↗
DOE OSTI2020

Mechanistic Understanding and Rational Design of Quantum Dot/Mediator Interfaces for Efficient Photon Upconversion

The semiconductor-nanocrystal-sensitized, three-component upconversion system has made great strides over the past 5 years. The three components (i.e., triplet photosensitizer, mediator, and emitter) each play critical roles in determining the input and output photon energy and overall quantum efficiency (QE). The nanocrystal photosensitizer converts the absorbed photon into singlet excitons and then triplet excitons via intersystem crossing. The mediator accepts the triplet exciton via either direct Dexter-type triplet energy transfer (TET) or sequential charge transfer (CT) while extending the exciton lifetime. Through a second triplet energy-transfer step from the mediator to the emitter, the latter is populated in its lowest excited triplet state. Triplet–triplet annihilation (TTA) between two triplet emitters generates the emitter in its bright singlet state, which then emits the upconverted photon. Quantum dots (QD) have a tunable band gap, large extinction coefficient, and small singlet–triplet energy losses compared to metal–ligand charge-transfer complexes. This high triplet exciton yield makes QDs good candidates for photosensitizers. In terms of driving triplet energy transfer, the triplet energy of the mediator should be slightly lower than the triplet exciton energy of the QD sensitizer for a downhill energy landscape with minimal energy loss. The same energy cascade is also required for the transfer from the mediator to the emitter. Lastly, the triplet energy of the emitter must be slightly larger than one-half of its singlet energy to ensure that TTA is exothermic. Optimization of the sensitizer, mediator, and emitter will lead to an increase in the anti-Stokes shift and the total quantum efficiency. Evaluating each individual step’s efficiency and kinetics is necessary for the understanding of the limiting factors in existing systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Anthracene Diphosphate Ligands for CdSe Quantum Dots; Molecular Design for Efficient Upconversion

Quantum dot (QD)-sensitized photon upconversion follows a multi-step energy transfer process from the QD to transmitter ligand to a soluble annihilator. Using a novel 10-R-anthracene-1,8-diphosphoric acid (R = octyl, 2- hexyldecyl, phenyl) ligand with high binding affinity for CdSe QD surfaces, we demonstrate a photon upconversion process that is limited by the transmitter to annihilator transfer efficiency. Using 1 H NMR spectroscopy, we demonstrate that these bidentate diphosphate ligands rapidly and irreversibly displace two carboxylate ligands. These ligands mediate energy transfer from the photoexcited QDs to a triplet annihilator (1,10-diphenylanthracene), producing overall photon upconversion quantum efficiencies as high as 17%, the highest for QDs with no shells. In conclusion, transient absorption spectroscopy shows that the anthracene dihydrogen phosphate (ADP) ligand supports a 3.4 fold longer triplet state lifetime compared to 9-anthracene carboxylic acid (299.9 ± 9.5 vs 88.2 ± 2.1 μs), increasing the probability of energy transfer.

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

Y(III) Sorption at the Orthoclase (001) Surface Measured by X-ray Reflectivity

Interactions of heavy metals with charged mineral surfaces control their mobility in the environment. Here, we investigate the adsorption of Y(III) onto the orthoclase (001) basal plane, the former as a representative of rare earth elements and an analogue of trivalent actinides and the latter as a representative of naturally abundant K-feldspar minerals. In this study, we apply in situ high-resolution X-ray reflectivity to determine the sorption capacity and molecular distribution of adsorbed Y species as a function of the Y 3+ concentration, [Y 3+ ], at pH 7 and 5. With [Y 3+ ] ≥ 1 mM at pH 7, we observe an inner-sphere (IS) sorption complex at a distance of ~1.5 Å from the surface and an outer-sphere (OS) complex at 3–4 Å. Based on the adsorption height of the IS complex, a bidentate, binuclear binding mode, in which Y 3+ binds to two terminal oxygens, is proposed. In contrast, mostly OS sorption is observed at pH 5. The observed maximum Y coverage is ~1.3 Y 3+ /A UC (A UC : area of the unit cell = 111.4 Å 2 ) for all the investigated pH values and Y concentrations, which is in the expected range based on the estimated surface charge of orthoclase (001).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Laser-Induced Thermal Decomposition of Uranium Coordination Compounds with Non-oxidic Ligands to Produce Nitride and Carbide Materials

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds—UI 4 (TMEDA) 2 , UCl 4 (TMEDA) 2 , UCl 3 (pyridine) x , and UI 3 (pyridine) 4 . Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 °C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Excitation Wavelength-Dependent Emission from Americium(III) in Mineral Acid Solutions

The photoluminescence behavior of trivalent americium, Am(III), in mineral acid solutions is reported under direct-metal excitation at seven high-energy wavelengths in the ultraviolet and visible regions (378-512 nm). This study revealed a dependence of the Am(III)-based visible emission profile on the chosen excitation wavelength. For example, excitation at the more common wavelength of 504 nm produces the two expected emission bands: one at approximately 600 nm (5D1' to 7F0') and another at 690 nm (5D1' to 7F1'). When the excitation wavelength is shifted to 398 nm (targeting the 5D3', 5H7' from 7F0' transitions), the emission occurs almost exclusively at 600 nm. This behavior is unexpected and potentially highlights fundamental knowledge gaps in the current understanding of the intraconfigurational 5f-5f electronic transitions that give rise to Am(III) photoluminescence. Although a full interpretation of these results is limited by the incomplete understanding of Am(III) speciation in mineral acid systems, this study explores several potential explanations for the observed behavior and challenges the widely held assumption of a single emissive Am(III) species.

Americium↗
DOE OSTI2022

Theoretical and Experimental Study of the Spectroscopy and Thermochemistry of UC +/0/–

A combination of high-level ab initio calculations and anion photoelectron detachment (PD) measurements is reported for the UC, UC – , and UC + molecules. To better compare the theoretical values with the experimental photoelectron spectrum (PES), a value of 1.493 eV for the adiabatic electron affinity (AEA) of UC was calculated at the Feller–Peterson–Dixon (FPD) level. The lowest vertical detachment energy (VDE) is predicted to be 1.500 eV compared to the experimental value of 1.487 ± 0.035 eV. A shoulder to lower energy in the experimental PD spectrum with the 355 nm laser can be assigned to a combination of low-lying excited states of UC – and excited vibrational states. The VDEs calculated for the low-lying excited electronic states of UC at the SO-CASPT2 level are consistent with the observed additional electron binding energies at 1.990, 2.112, 2.316, and 3.760 eV. Potential energy curves for the Ω states and the associated spectroscopic properties are also reported. Compared to UN and UN + , the bond dissociation energy (BDE) of UC (411.3 kJ/mol) is predicted to be considerably lower. The natural bond orbitals (NBO) calculations show that the UC 0/+/– molecules have a bond order of 2.5 with their ground-state configuration arising from changes in the oxidation state of the U atom in terms of the 7s orbital occupation: UC (5f 2 7s 1 ), UC – (5f 2 7s 2 ), and UC + (5f 2 7s 0 ). Furthermore, the behavior of the UN and UC sequence of molecules and anions differs from the corresponding sequences for UO and UF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Revealing the Three-Dimensional Orientation and Interplay between Plasmons and Interband Transitions for Single Gold Bipyramids by Photoluminescence Excitation Pattern Imaging

Gold bipyramids (AuBPs) attract significant attention due to the large enhancement of the electric field around their sharp tips and well-defined tunability of their plasmon resonances. Excitation patterns of single AuBPs are recorded using raster-scanning confocal microscopy combined with radially and azimuthally polarized laser beams. Photoluminescence spectra (PL) and excitation patterns of the same AuBP are acquired with three different excitation wavelengths. Here, the isotropic excitation patterns suggest that the AuBPs are mainly excited by interband transitions with 488/530 nm radiation, while excitation patterns created with a 633 nm laser exhibit a double lobed shape that indicates a single dipole excitation process associated with the longitudinal plasmon resonance mode. We are able to determine the three-dimensional orientation of single AuBPs nonperturbatively by comparing experimental patterns with theoretical simulations. The asymmetric patterns show that the AuBPs are lying on the substrate with an out-of-plane tilt angle of around 10° to 15°.

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

Quantifying the Ligand-Induced Triplet Energy Transfer Barrier in a Quantum Dot-Based Upconversion System

During photon upconversion, quantum dots (QDs) transfer energy to molecules in solution through a long ligand shell. This insulating ligand shell imparts colloidal stability at the expense of efficient photosensitization. For the first time, we quantify the barrier these aliphatic ligands pose for triplet energy transfer in solution. Using transient absorption spectroscopy, we experimentally measure a small damping coefficient of 0.027 Å −1 for a ligand exceeding 10 carbons in length. The dynamic nature of ligands in solution lowers the barrier to charge or energy transfer compared to organic thin films. In addition, we show that surface ligands shorter than 8 carbons in length allow direct energy transfer from the QD, bypassing the need for a transmitter ligand to mediate energy transfer, leading to a 6.9% upconversion quantum yield compared with 0.01% for ligands with 18 carbons. Furthermore, this experimentally derived insight will enable the design of efficient QD-based photosensitizers for catalysis and energy conversion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

High-Level Reverse Intersystem Crossing and Molecular Rigidity Improve Spin Statistics for Triplet–Triplet Annihilation Upconversion

The structural factors affecting triplet−triplet annihilation (TTA) at the molecular level are not well-understood. Here, our steady-state photoluminescence and transient absorption results demonstrate that the spin statistical factor, η, decreases from 0.60 to 0.46 and 0.14 going from 9,10-diphenylanthracene (DPA) to the 1,5-DPA and 2,6-DPA isomers, respectively, during photon upconversion with a platinum octaethylporphyrin sensitizer. Density functional theory (DFT) shows that η depends on the energetics of hot triplet states and molecular rigidity. The significantly high conical intersection energy between the S 0 and T 1 states for 9,10-DPA gives its longer triplet lifetime. Time-dependent DFT calculations show that 9,10-DPA and 1,5-DPA can undergo high-level reverse intersystem crossing from their T 2 and T 3 states, respectively, to the bright S 1 state, increasing the limit of the spin statistical factor. Both factors ultimately serve to enhance the TTA efficiency. Furthermore, this work provides insight into designing molecules for efficient light-emitting and photon upconversion applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗