Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals

The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu3+-doped BaZrO3 (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange–red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon 5D0 → 7F0 transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu3+ concentrations of 0–10.0%. The 2.0% Eu3+-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu3+ ions occupy the six-coordinated Zr4+ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties. View Full-Tex

X-ray absorption spectroscopy elucidates the impact of structural disorder on electron mobility in amorphous zinc-tin-oxide thin films

We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes.United States. Office of Naval Research (ONR N00014-10-1-0937)National Science Foundation (U.S.) (Award CBET-1032955)National Science Foundation (U.S.) (CAREER Award ECCS-1150878

Retrospective evaluation of whole exome and genome mutation calls in 746 cancer samples

Funder: NCI U24CA211006Abstract: The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) curated consensus somatic mutation calls using whole exome sequencing (WES) and whole genome sequencing (WGS), respectively. Here, as part of the ICGC/TCGA Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium, which aggregated whole genome sequencing data from 2,658 cancers across 38 tumour types, we compare WES and WGS side-by-side from 746 TCGA samples, finding that ~80% of mutations overlap in covered exonic regions. We estimate that low variant allele fraction (VAF < 15%) and clonal heterogeneity contribute up to 68% of private WGS mutations and 71% of private WES mutations. We observe that ~30% of private WGS mutations trace to mutations identified by a single variant caller in WES consensus efforts. WGS captures both ~50% more variation in exonic regions and un-observed mutations in loci with variable GC-content. Together, our analysis highlights technological divergences between two reproducible somatic variant detection efforts

Excitation-Dependent Photoluminescence of BaZrO3:Eu3+ Crystals

The elucidation of local structure, excitation-dependent spectroscopy, and defect engineering in lanthanide ion-doped phosphors was a focal point of research. In this work, we have studied Eu3+-doped BaZrO3 (BZOE) submicron crystals that were synthesized by a molten salt method. The BZOE crystals show orange&ndash;red emission tunability under the host and dopant excitations at 279 nm and 395 nm, respectively, and the difference is determined in terms of the asymmetry ratio, Stark splitting, and intensity of the uncommon 5D0 &rarr; 7F0 transition. These distinct spectral features remain unaltered under different excitations for the BZOE crystals with Eu3+ concentrations of 0&ndash;10.0%. The 2.0% Eu3+-doped BZOE crystals display the best optical performance in terms of excitation/emission intensity, lifetime, and quantum yield. The X-ray absorption near the edge structure spectral data suggest europium, barium, and zirconium ions to be stabilized in +3, +2, and +4 oxidation states, respectively. The extended X-ray absorption fine structure spectral analysis confirms that, below 2.0% doping, the Eu3+ ions occupy the six-coordinated Zr4+ sites. This work gives complete information about the BZOE phosphor in terms of the dopant oxidation state, the local structure, the excitation-dependent photoluminescence (PL), the concentration-dependent PL, and the origin of PL. Such a complete photophysical analysis opens up a new pathway in perovskite research in the area of phosphors and scintillators with tunable properties

In Situ EXAFS-Derived Mechanism of Highly Reversible Tin Phosphide/Graphite Composite Anode for Li-Ion Batteries

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A novel Sn4P3/graphite composite anode material with superior capacity and cycling performance (651 mA h g−1 after 100 cycles) is investigated by in situ X-ray absorption spectroscopy. Extended X-ray absorption fine structure modeling and detailed analysis of local environment changes are correlated to the cell capacity and reveal the mechanism of lithiation/delithiation process. Results show that in the first two lithiation/delithiation cycles crystalline Sn4P3 is fully converted to an amorphous SnPx phase, which in further cycles participates in reversible conversion and alloying reactions. The superior reversibility of this material is attributed to the highly dispersed SnPx in the graphite matrix, which provides enhanced electrical conductivity and prevents aggregation of Sn clusters during the lithiation/delithiation process. The gradual capacity fading in long-term cycling is attributed to the observed increase in the size and the amount of metallic Sn clusters in the delithiated state, correlated to the reduced recovery of the SnPx phase. This paper reveals the mechanism responsible for the highly reversible tin phosphides and provides insights for improving the capacity and cycle life of conversion and alloying materials

Potential-Resolved In Situ X‑ray Absorption Spectroscopy Study of Sn and SnO₂ Nanomaterial Anodes for Lithium-Ion Batteries

This work provides detailed analysis of processes occurring in metallic Sn and SnO₂ anode materials for lithium ion batteries during first lithiation, studied in situ with rapid continuous X-ray absorption spectroscopy (XAS). The X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra provide information on dynamic changes in the Sn atomic environment, including type and number of neighboring atoms and interatomic distances. A unique methodology was used to model insertion of Li atoms into the electrode material structure and to analyze the formation of SnLi phases within the electrodes. Additionally, analysis of fully lithiated and delithiated states of Sn and SnO₂ electrodes in the first two cycles provides insight into the reasons for poor electrochemical performance and rapid capacity decline. Results indicate that use of SnO₂ is more promising than metallic Sn as an anode material, but more effort in nanoscale and atomic engineering of anodes is required for commercially feasible use of Sn-based materials

In Situ X‑ray Absorption Spectroscopy Study of the Capacity Fading Mechanism in Hybrid Sn₃O₂(OH)₂/Graphite Battery Anode Nanomaterials

In situ X-ray absorption spectroscopy (XAS) of an electrode material under electrochemical control has enabled a detailed examination of the capacity fading mechanism during charge–discharge cycling in a hybrid nanomaterial, Sn₃O₂(OH)₂/graphite, that is considered for use as a high-capacity lithium-ion battery anode. By the use of an original one-pot solvothermal synthesis technique, Sn₃O₂(OH)₂ nanoparticles were directly deposited on the surface of nanothin graphite and were charged/discharged in situ for several cycles while XAS spectra at the Sn K-edge were taken. Modeling of the collected extended X-ray absorption fine structure (EXAFS) spectra provides detailed information on the Sn–O, Sn–Sn, and Sn–Li coordination numbers and atomic distances for each charged and discharged electrode state. On the basis of electrochemical data and the changes in atomic arrangement deduced from the EXAFS fitting results, including the first unambiguous observation of Sn–Li near neighbors, a capacity fading mechanism is proposed that is different from widely accepted volume expansion for tin metal and tin oxides. Our experimental results suggest that atomic clusters of metallic tin surrounded by highly disordered Li₂O shells are formed on first charge. The metallic tin clusters participate in lithiation and delithiation on the following charge/discharge cycles; however, because of continued segregation of tin and Li₂O phases, the tin clusters eventually lose electrical contact with the rest of the electrode and become excluded from further participation in electrochemical reactions, resulting in reduced capacity of this anode material