Neodymium and Erbium Coordination Environments in Phosphate Glasses

The local structures of Nd3+ and Er3+ ions in two series of rare-earth (RE) phosphate glasses with nominal compositions xR203-(1-x)P2O5, where R=Nd and Er and 0.05≤x≤0.28, have been characterized by LIII-edge extended x-ray-absorption fine-structure spectroscopy (EXAFS). The RE coordination number depends on the R2O3 content, decreasing from 9.0 (10) oxygen nearest neighbors in ultraphosphate compositions (x\u3c0.15) to 6.4 (9) oxygen nearest neighbors for the metaphosphate (x∼0.25) compositions. The average Er-O bond distance decreases from 2.29 (1) to 2.23 (1) Å, and the average Nd-O bond distance decreases from 2.40 (1) to 2.37 (1) Å over the same compositional range. The changes in coordination environments are consistent with the conversion of isolated RE polyhedra to clustered RE polyhedra sharing common oxygens as the number of available terminal oxygens per RE ion decreases with increasing x

Electronic properties of hybrid organic/inorganic semiconductor pn-junctions

Hybrid inorganic/organic semiconductor heterojunctions are candidates to expand the scope of purely organic or inorganic junctions in electronic and optoelectronic devices. Comprehensive understanding of bulk and interface doping on the junction’s electronic properties is therefore desirable. In this work, we elucidate the energy level alignment and its mechanisms at a prototypical hybrid pn-junction comprising ZnO (n-type) and p-doped N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) as semiconductors, using photoelectron spectroscopy. The level alignment can be quantitatively described by the interplay of contact-induced band and energy level bending in the inorganic and organic component away from the interface, and an interface dipole due to the push-back effect. By adjusting the dopant concentration in α-NPD, the position of the frontier energy levels of ZnO can be varied by over 0.5 eV and that of α-NPD by over 1 eV. The tunability of this pn-junction’s energy levels evidences the substantial potential of the hybrid approach for enhancing device functionality.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Peer Reviewe

Modifier Effects on the Properties and Structures of Aluminophosphate Glasses

Properties and structures of potassium, barium and magnesium alumino-metaphosphate glasses (O/P≈3) have been investigated. Adding Al(PO3)3 to an alkali or alkaline earth metaphosphate glass improves the chemical durability, increases the glass transition temperature and reduces thermal expansion and residual OH-content. Infrared spectra are dominated by metaphosphate vibrational modes, the frequencies of which are dependent on the field strengths of the modifying cations. 27Al MAS NMR spectroscopy indicates that aluminum ions are incorporated into the aluminophosphate network primarily in octahedral sites, although tetrahedral and pentahedral sites are also present. The average aluminum co-ordination number decreases in the series K+\u3eBa2+\u3eMg2+ and this is related to a reduction in the basicity of glasses with higher field strength modifiers. © 2001 Published by Elservier Science B.V

Structure and Properties of Lanthanum-Aluminum-Phosphate Glasses

Glass-forming characteristics, properties and structural features of glasses in the La2O3-Al2O3-P2 O5 system have been investigated. The glass-forming region is small compared to the Na2O-Al2O3-P2O5 system. Glass transition temperature increases and thermal expansion coefficient, refractive index, and density all decrease as the alumina content of the glass is increased. Infrared (IR) spectroscopy indicates that the glass network is dominated by bridging P-tetrahedra with terminal tetrahedra present in glasses with O/P ratios \u3e 3. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy indicates that Al ions are incorporated in these glasses in 4-, 5-, and 6-coordinated sites. The average Al-coordination number (CN) increases with an increase in the Al/La ratio and decreases with an increase in the O/P ratio. Both trends can be explained by the avoidance of Al-O-Al bonds in the glass structure. © 2001 Elsevier Science B.V

Cation Effects on Anion Distributions in Aluminophosphate Glasses

Alkali aluminophosphate glasses, including those in the system xAl2O3·(1-x)CsPO3 (0 ≤ x ≤ 0.25), were examined by high-performance liquid chromatography (HPLC), infrared (IR), and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Phosphate anions become progressively shorter with the addition of alumina to a metaphosphate glass. Al3+ ions are initially incorporated into the structure in octahedral sites, but the average Al coordination number (CN) decreases with increasing alumina content and tetrahedral species are the preferred moiety when [O]/[P] \u3e 3.5. Al[4] sites appear to be associated with monophosphate (Q0) anions. The role of modifier size on aluminophosphate structure is investigated. At low alumina content (\u3c 15 mol%), the disproportionation of pyrophosphate anions into triphosphate and orthophosphate anions is responsible for the lower average Al CN of cesium aluminophosphate glasses compared with sodium aluminophosphate glasses

High-energy X-ray Diffraction Study of La Co-ordination in Lanthanum Phosphate Glasses

Differences in La co-ordination environments indicated in the structures of rare earth-phosphate crystals in glasses with compositions ranging from ultraphosphate to metaphosphate stoichiometries were investigated. A series of lanthanum phosphate glasses were characterized by X-ray diffraction analysis and a change of the La-O co-ordination number was extracted by Gaussian fitting of the first-neighbor distances. The decrease in co-ordination number was due to the transition of ultraphosphate glass structures to metaphosphate structures. The changes in the La environments explained the compositional dependence of glass properties

In Operando Small-Angle Neutron Scattering Study of Single-Ion Copolymer Electrolyte for Li-Metal Batteries

International audienc

Porphyrin adsorption and ligand exchange at the (110)-TiO2_2 / organic liquid interface

Highly efficient dye-sensitized solar cells (DSSCs) have been prepared on the basis of porphyrin dyes with significant success. Recent studies have demonstrated a correlation between the solar cell efficiency and the configuration of the adsorbed porphyrin molecules at the surface of the semiconducting support material. The preparation of dense self assembled monolayers (SAMs) of upright standing porphyrin molecules on TiO$_2$ surfaces was achieved from toluene solutions only when using a molecular exchange reaction. Here, an exchange study of an oleic acid (OLA) SAM on a $$ TiO$_2$ surface by porphyrin molecules is presented. The exchange reaction has been studied by ex-situ as well as in-situ X-ray reflectometry (XRR) measurements. It was found that an almost complete exchange of OLA with porphyrins can be achieved. With increasing coating times the orientation of the porphyrin molecules relative to the substrate surface changed from flat lying to upright standing

First Step into Space: Performance and Morphological Evolution of P3HT:PCBM Bulk Heterojunction Solar Sells under AM0 Illumination

P3HT (poly(3-hexylthiophene-2,5-diyl)):$PC_{61}BM$ ([6,6]-phenyl-C61 butyric acid methyl ester) bulk heterojunction solar cells are fabricated and characterized as a function of solar intensity, temperature, and aging at vacuum conditions under illumination with AM0 illumination for testing potential use in space applications. The evolution of the inner film morphology is probed with grazing incidence X-ray scattering techniques and correlated with the evolution of the efficiency during aging. Grazing incidence wide-angle X-ray scattering shows almost no change of the crystalline structure of the P3HT:PCBM films due to aging. In contrast, the morphological evolution on the mesoscale extracted from grazing incidence small-angle X-ray scattering can explain the observed decay of the overall efficiency. The behavior at high solar intensities as well as elevated temperatures suggests that organic solar cells have high potential for space applications in the future