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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Electronic structure and optical properties of CdS{sub x}Se{sub 1−x} solid solution nanostructures from X-ray absorption near edge structure, X-ray excited optical luminescence, and density functional theory investigations

The electronic structure and optical properties of a series of iso-electronic and iso-structural CdS{sub x}Se{sub 1−x} solid solution nanostructures have been investigated using X-ray absorption near edge structure, extended X-ray absorption fine structure, and X-ray excited optical luminescence at various absorption edges of Cd, S, and Se. It is found that the system exhibits compositions, with variable local structure in-between that of CdS and CdSe accompanied by tunable optical band gap between that of CdS and CdSe. Theoretical calculation using density functional theory has been carried out to elucidate the observations. It is also found that luminescence induced by X-ray excitation shows new optical channels not observed previously with laser excitation. The implications of these observations are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Nonlinear luminescence response of CaF{sub 2}:Eu and YAlO{sub 3}:Ce to single-ion excitation

Understanding scintillation physics and nonproportionality is essential to accelerate materials discovery that has been restricted due to the difficulties inherent to large crystal growth and complex nature of gamma-solid interaction. Taking advantage of less restrictive growth and deposition techniques for smaller crystal sizes or thin films and better fundamental understanding of ion-solid interactions, a unique ion approach is demonstrated to effectively screen candidate scintillators with relatively small size and evaluate their nonlinear scintillation response. Response of CaF{sub 2}:Eu and YAlO{sub 3}:Ce scintillators to single ions of H{sup +}, He{sup +}, and O{sup 3+} are measured by the corresponding pulse height over a continuous energy range using a time-of-flight–scintillator–photoelectric multiplier tube apparatus. Nonlinear response of the scintillators under ionizing ion irradiation is quantitatively evaluated by considering the energy partitioning process. In a differential energy deposition region with negligible displacement damage, the low, medium and high excitation energy deposition density (D{sub exci}) can be produced by energetic H{sup +}, He{sup +} and O{sup 3+} ions, respectively, and significantly different impacts on the response characteristics of these two benchmark scintillators are observed. For CaF{sub 2}:Eu, the scintillation efficiency under ion irradiation monotonically decreases with increasing excitation-energy density. In contrast, the response efficiency of YAlO{sub 3}:Ce scintillation initially increases with excitation-energy density at low excitation-energy densities, goes through a maximum, and then decreases with further increasing excitation-energy density. The fundamental mechanism causing these different response behaviours in the scintillators is based on the competition between the scintillation response and the nonradiative quenching process under different excitation densities, which is also the main origin of the nonlinear response of the scintillators to irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A simple and green strategy for preparing luminescent Tb{sup 3+} complex-based nanocomposite with stable luminescence in water

Graphical abstract: A water-soluble Tb{sup 3+} complex-based nanocomposite has been prepared through a simple and green method, showing good luminescence stability in aqueous environment and highly selective sensing ability for THF in water. - Highlights: • A new Tb(III) hybrid material with bright green luminescence was prepared through a very simple and green procedure. • The material exhibits good luminescence stability in aqueous solution. • The material can be applied for detecting low THF content (0.1–6.0 vol%) in aqueous solution. - Abstract: Luminescent lanthanide-based nanocomposites (LnNCs) with intense and stable luminescence in aqueous media are in high demand for sensing and biological applications. Herein we report a new water-soluble LnNCs that prepared through a very simple and green procedure, with bright green luminescence dominated by {sup 5}D{sub 4} → {sup 7}F{sub 5} transition (542 nm) of Tb{sup 3+}, showing improved luminescence behavior compared with the complex Tb(Sal){sub 3}·2H{sub 2}O (Sal = salicylic acid) and good luminescence stability in aqueous solution even for considerable time (3 weeks) ascribed to the protective effect of the clay substrate to the Tb{sup 3+} complex. Moreover, the material exhibits rapid and highly selective sensing of tetrahydrofuran (THF) and can be applied for detecting low THF content (0.1–6.0 vol%) in aqueous solution.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Low-temperature luminescence and thermally stimulated luminescence of BeO: Mg single crystals

Luminescence and thermally stimulated luminescence (TL) of BeO: Mg crystals are studied at T = 6–380 K. The TL glow curves and the spectra of luminescence (1.2–6.5 eV), luminescence excitation, and reflection (3.7–20 eV) are obtained. It is found that the introduction of an isovalent magnesium impurity into BeO leads to the appearance of three new broad luminescence bands at 6.2–6.3, 4.3–4.4, and 1.9–2.6 eV. The first two are attributed to the radiative annihilation of a relaxed near-impurity (Mg) exciton, the excited state of which is formed as a result of energy transfer by free excitons. The impurity VUV and UV bands are compared with those for the intrinsic luminescence of BeO caused by the radiative annihilation of self-trapped excitons (STE) of two kinds: the band at 6.2–6.3 eV of BeO: Mg is compared with the band at 6.7 eV (STE{sub 1}) of BeO, and the band at 4.3–4.4 eV is compared with the band at 4.9 eV (STE{sup 2}) of BeO. In the visible region, the luminescence spectrum is due to a superposition of intracenter transitions in an impurity complex including a magnesium ion. The manifestation of X-ray-induced luminescence bands at T = 6 K in BeO: Mg indicates their excitation during band-to-band transitions and in recombination processes. The energy characteristics of the impurity states in BeO: Mg are determined; the effect of the isovalent impurity on the fluctuation rearrangement of the BeO: Mg structure in the thermal transformation region of STE{sub 1} → STE{sub 2} is revealed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Luminescent microporous metal–organic framework with functional Lewis basic sites on the pore surface: Quantifiable evaluation of luminescent sensing mechanisms towards Fe{sup 3+}

A systematic study has been conducted on a novel luminescent metal-organic framework, ([Zn(bpyp)(L-OH)]·DMF·2H{sub 2}O){sub n} (1), to explore its sensing mechanisms to Fe{sup 3+}. Structure analyses show that compound 1 exist pyridine N atoms and -OH groups on the pore surface for specific sensing of metal ions via Lewis acid-base interactions. On this consideration, the quenching mechanisms are studied and the processes are controlled by multiple mechanisms in which dynamic and static mechanisms are calculated, achieving the quantification evaluation of the quenching process. This work not only achieves the quantitative evaluation of the luminescence quenching but also provides certain insights into the quenching process, and the possible mechanisms explored in this work may inspire future research and design of target luminescent metal-organic frameworks (LMOFs) with specific functions. - Graphical abstract: A systematic study has been conducted on a novel luminescent metal-organic framework to explore its sensing mechanisms to Fe{sup 3+}. The quenching mechanisms are studied and the processes are controlled by multiple mechanisms in which dynamic and static mechanisms are calculated, achieving the quantification evaluation of the quenching process. - Highlights: • A novel porous luminescent MOF containing uncoordinated groups in interlayer channels was successfully synthesized. • The compound 1 can exhibit significant luminescent sensitivity to Fe{sup 3+}, which make its good candidate as luminescent sensor. • The corresponding dynamic and static quenching constants are calculated, achieving the quantification evaluation of the quenching process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A novel phosphor CaZnGe2O6:Bi3+ with persistent luminescence and photo-stimulated luminescence

Highlights: • The CaZnGe{sub 2}O{sub 6}: Bi{sup 3+} with the emission bands at 468 nm. • The afterglow emission band (300–650 nm) almost covering the UV–vis spectral region. • A afterglow time can last 12 h in the dark after ceasing the 254 nm irradiation. • The excitation of VIS-NIR incoherent light can get the photo-stimulated luminescence. - Abstract: Bi{sup 3+}-activated phosphor with ultraviolet-visible persistent luminescence and photo-stimulated luminescence is synthesized via high temperature solid phase reaction. This phosphor shows a broad emission band from 300 nm to 700 nm, a bright persistent luminescence over 12 h after ceasing the excitation and the photo-stimulated luminescence under the excitation of visible to near-infrared light. This paper reports that the operational waveband of long persistent phosphor, CaZnGe{sub 2}O{sub 6}: Bi{sup 3+}, has been extended into the short-wavelength spectral region.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Direct Aqueous-Phase Synthesis of Sub-10 nm “Luminous Pearls” with Enhanced in vivo Renewable Near-Infrared persistent luminescence

Near-infrared persistent luminescence nanoparticles (PLNPs) possess unique near-infrared persistent luminescence properties. They have recently been emerging as important materials for a wide variety of applications in chemistry and biology. Yet, they must endure high-temperature solid-state annealing reactions and subsequent complicated physical post-treatments. Herein, we report on a first direct aqueous-phase chemical synthesis route of NIR PLNPs and present their enhanced in vivo renewable near-infrared persistent luminescence. Our method leads to monodisperse PL nanoparticles as small as ca. 8 nm. More importantly, such sub-10 nm nanocrystals are readily dispersed, functionalized as well as form stable colloidal solutions in aqueous solution and cell culture medium for biological applications. Under bio-tissue penetrable red-light excitation, we found that such nanocrystals possess superior renewable PL photoluminescence in vitro and in vivo than current larger counterparts made by existing methods. We believe that this solid-state-reaction-free chemical approach overcomes the current key roadblock in regard to PLNP development, and thus will pave the way to broad use of these advanced miniature “luminous pearls” in photonics and biophotonics.

Luminous Pearls, Near-Infrared persistent luminesc↗
DOE OSTI2014

Luminescent properties of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} and its luminescence improvement by incorporating A{sup +} (A=Li, Na, and K)

A novel green phosphor SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is synthesized by a high temperature solid-state method, and its luminescent property is investigated. X-ray diffraction patterns of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} indicate a similarity crystalline phase to SrZn{sub 2}(PO{sub 4}){sub 2}. SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} shows green emission under 369 nm excitation, and the prominent luminescence in green (544 nm) due to {sup 5}D{sub 4}–{sup 7}F{sub 5} transition of Tb{sup 3+}. For the 544 nm emission, excitation spectrum has several excitation band from 200 nm to 400 nm. Emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} is influenced by Tb{sup 3+} concentration, and concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is also observed. With incorporating A{sup +} (A=Li, Na, and K) as compensator charge, the emission intensity of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can be obviously enhanced. CIE color coordinates of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} locate in the green region. The results indicate this phosphor may be a potential application in white LEDs. - Graphical abstract: SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation, and its luminescent properties can be improved by incorporating A{sup +} (A=Li, Na, and K). - Highlights: • SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} can produce green emission under near-UV excitation. • Concentration quenching effect of Tb{sup 3+} in SrZn{sub 2}(PO{sub 4}){sub 2} is observed. • Emission intensities of SrZn{sub 2}(PO{sub 4}){sub 2}:Tb{sup 3+} are enhanced by codoped A{sup +} (A=Li, Na, K)

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

Luminescence of a Polymer Composite Doped with Boron Chelates. Mechanism of Luminescence Sensitization

It has been revealed that a sensitized luminescence of AntAcBF{sub 2} is observed in the boron difluoride dibenzoylmethanate (DBMBF{sub 2})–boron difluoride anthracenoylacetonate (AntAcBF{sub 2}) system in the polystyrene matrix. The emission mechanism of energy transfer from DBMBF{sub 2} to AntAcBF{sub 2} has been established. The luminescence properties of bilayer films with one layer containing DBMBF{sub 2} and another one containing AntAcBF{sub 2} have been investigated. At luminophore contents in equimolar quantities, one observes a white luminescence of the bilayer polymer composite.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A series of Ln-p-chlorobenzoic acid–terpyridine complexes: lanthanide contraction effects, supramolecular interactions and luminescent behavior

Fifteen new lanthanide p-chlorobenzoic acid complexes, [PrL3(terpy)(H2O)]2 (1), [LnL3(terpy)(H2O)]2 (Ln = Nd (2), Sm (3), and Eu (4)), and [LnL3(terpy)(H2O)] (Ln = Sm (3'), Eu (4'), Gd (5), Tb (6), Dy (7), Ho (8), Er (9), Tm (10), Yb (11), Lu (12), and Y (13); HL: p-chlorobenzoic acid; terpy: 2,2':6',2''-terpyridine), have been synthesized hydrothermally at varying temperatures and structurally characterized by single crystal and powder X-ray diffraction. The series is comprised of binuclear molecular units (Pr–Eu) that give way to mononuclear molecular complexes (Sm–Y) as the lanthanide contraction takes effect. All fifteen complexes feature a tridentate terpyridine ligand, p-chlorobenzoic acid ligands exhibiting multiple binding modes, bidentate, bridging bidentate, and monodentate, and a bound water molecule. Binuclear complexes 1–4 are stitched together via intermolecular interactions: aromatic–aromatic interactions for 1, halogen•••halogen interactions for 2–4, to form 1D chains. Mononuclear complexes 3', 4', and 5–13 utilize supramolecular hydrogen and halogen bonding to form 2D sheets. Visible and near-IR solid state luminescence studies were performed on complexes 2, 3, 3', 4, 4', 6, 7 and 11 and the characteristic visible luminescence of Sm(III), Eu(III), Tb(III), and Dy(III) was exhibited. The near-IR spectra of the Nd(III) and Yb(III) complexes exhibit weak characteristic luminescence, showing that terpy can act as a sensitizing chromophore in these systems.

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

Highly Selective Colorimetric and Luminescence Response of a Square-Planar Platinum(II) Terpyridyl Complex to Aqueous TcO 4 –

Molecular recognition of an aqueous pertechnetate (TcO 4 – ) anion is fundamentally challenging partly due to the charge-diffuse nature of this anion, which hampers design of new technologies for its separation and detection. Here, to address this gap, simple salts of transition metal complexes that undergo a distinct spectroscopic change upon exposure to aqueous anions were explored. The Pt(II) complex [Pt(tpy)Br]SbF 6 (tpy = 2,2′;6′,2″-terpyridine) undergoes a dramatic color change and intense luminescence response upon TcO 4 – uptake due to concomitant enhancement of Pt···Pt interactions. The spectroscopic response was highly selective and quantitative for aqueous TcO 4 – among other competing anions. Complementary Raman spectroscopy and microscopy techniques, structural determination, and theoretical methods were employed to elucidate the mechanism of this response at the molecular level.

anions↗
DOE OSTI2014

Intervalence charge transfer luminescence: The anomalous luminescence of cerium-doped Cs{sub 2}LiLuCl{sub 6} elpasolite

The existence of intervalence charge transfer (IVCT) luminescence is reported. It is shown that the so called anomalous luminescence of Ce-doped elpasolite Cs{sub 2}LiLuCl{sub 6}, which is characterized mainly by a very large Stokes shift and a very large band width, corresponds to an IVCT emission that takes place in Ce{sup 3+}–Ce{sup 4+} pairs, from the 5de{sub g} orbital of Ce{sup 3+} to 4f orbitals of Ce{sup 4+}. Its Stokes shift is the sum of the large reorganization energies of the Ce{sup 4+} and Ce{sup 3+} centers formed after the fixed-nuclei electron transfer and it is equal to the energy of the IVCT absorption commonly found in mixed-valence compounds, which is predicted to exist in this material and to be slightly larger than 10 000 cm{sup −1}. The large band width is the consequence of the large offset between the minima of the Ce{sup 3+}–Ce{sup 4+} and Ce{sup 4+}–Ce{sup 3+} pairs along the electron transfer reaction coordinate. This offset is approximately 2√(3) times the difference of Ce–Cl equilibrium distances in the Ce{sup 3+} and Ce{sup 4+} centers. It is shown that the energies of the peaks and the widths of IVCT absorption and emission bands can be calculated ab initio with reasonable accuracy from diabatic energy surfaces of the ground and excited states and that these can be obtained, in turn, from independent calculations on the donor and acceptor active centers. We obtained the energies of the Ce{sup 3+} and Ce{sup 4+} active centers of Ce-doped Cs{sub 2}LiLuCl{sub 6} by means of state-of-the-art wave-function-theory spin-orbit coupling relativistic calculations on the donor cluster (CeCl{sub 6}Li{sub 6}Cs{sub 8}){sup 11+} and the acceptor cluster (CeCl{sub 6}Li{sub 6}Cs{sub 8}){sup 12+} embedded in a quantum mechanical embedding potential of the host. The calculations provide interpretations of unexplained experimental observations as due to higher energy IVCT absorptions, and allow to reinterpret others. The existence of another IVCT emission of lower energy, at around 14 000-16 000 cm{sup −1} less than the 5dt{sub 2g} emission, is also predicted.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Spectroelectrochemical Sensor for Spectroscopically Hard-to-detect Metals by in situ Formation of a Luminescent Complex Using Ru(II) as a Model Compound

Fast, robust, and cost-effective means of detecting spectroscopically inactive metal species are necessary for field detection and applications within a variety of areas including industry and the nuclear safeguards fields. A sensor based on spectroelectrochemistry is an excellent candidate to meet these needs as it provides improved selectivity for specifically quantifying metal ions by simultaneously monitoring at least two physio-chemical properties. Ruthenium was chosen as a model system for this study due to its spectroscopic and electrochemical characteristics as well as its relevance within the fuel cycle and industrial fields. Aqueous Ru displays multiple redox couples in which all available oxidation states have poor sensitivity for detection by visible absorption spectroscopy because of the low molar absorptivities. Ru can, however, form complexes with sensitizing ligands such as 2,2'-bipyridine, where the resulting [Ru(ligand)3]2+ complex displays a red luminescence with a high quantum yield of emission. This significantly improves detection limits for Ru and allows for the spectroelectrochemical detection of the otherwise hard-to-detect metal ion. This work explores the in-situ generation of Ru(bpy)3 complexes in simulated field samples and their subsequent spectroelectrochemical sensing using our sensor methodology.

Lines, Amanda M.↗