A novel method for the preparation of non-agglomerated nanometre sized particles of lanthanum phosphate phosphors utilising a high surface area support in the firing process

This journal is © The Royal Society of Chemistry 2012A convenient method is described that uses a quartz wool substrate to immobilise nanometre sized phosphor precursor particles enabling them to be fired at high temperature without sintering/agglomeration. The nanometre sized phosphor particles are easily removed from the substrate by re-dispersion into liquid for subsequent use.Biotechnology and biological sciences research council (BBSRC

Structure and morphology of ACEL ZnS:Cu,Cl phosphor powder etched by hydrochloric acid

© The Electrochemical Society, Inc. 2009. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version is available at the link below.Despite many researches over the last half century, the mechanism of ac powder electroluminescence remains to be fully elucidated and, to this end, a better understanding of the relatively complex structure of alternate current electroluminescence (ACEL) phosphors is required. Consequently, the structure and morphology of ZnS:Cu,Cl phosphor powders have been investigated herein by means of scanning electron microscopy (SEM) on hydrochloric acid-etched samples and X-ray powder diffraction. The latter technique confirmed that, as a result of two-stage firing during their synthesis, the phosphors were converted from the high temperature hexagonal (wurtzite) structure to the low temperature cubic (sphalerite) polymorph having a high density of planar stacking faults. Optical microscopy revealed that the crystal habit of the phosphor had the appearance of the hexagonal polymorph, which can be explained by the sphalerite pseudomorphing of the earlier wurtzite after undergoing the hexagonal to cubic phase transformation during the synthesis. SEM micrographs of the hydrochloric-etched phosphor particles revealed etch pits, a high density of planar stacking faults along the cubic [111] axis, and the pyramids on the (111) face. These observations were consistent with unidirectional crystal growth originating from the face showing the pyramids.EPSRC, DTI, and the Technology Strategy Board-led Technology Program

Multicolour correlative imaging using phosphor probes

Correlative light and electron microscopy exploits the advantages of optical methods, such as multicolour probes and their use in hydrated live biological samples, to locate functional units, which are then correlated with structural details that can be revealed by the superior resolution of electron microscopes. One difficulty is locating the area imaged by the electron beam in the much larger optical field of view. Multifunctional probes that can be imaged in both modalities and thus register the two images are required. Phosphor materials give cathodoluminescence (CL) optical emissions under electron excitation. Lanthanum phosphate containing thulium or terbium or europium emits narrow bands in the blue, green and red regions of the CL spectrum; they may be synthesised with very uniform-sized crystals in the 10- to 50-nm range. Such crystals can be imaged by CL in the electron microscope, at resolutions limited by the particle size, and with colour discrimination to identify different probes. These materials also give emissions in the optical microscope, by multiphoton excitation. They have been deposited on the surface of glioblastoma cells and imaged by CL. Gadolinium oxysulphide doped with terbium emits green photons by either ultraviolet or electron excitation. Sixty-nanometre crystals of this phosphor have been imaged in the atmospheric scanning electron microscope (JEOL ClairScope). This probe and microscope combination allow correlative imaging in hydrated samples. Phosphor probes should prove to be very useful in correlative light and electron microscopy, as fiducial markers to assist in image registration, and in high/super resolution imaging studies

MATRIX REACTIONS OF OXYGEN ATOMS WITH P4. INFRARED SPECTRA OF P4O, P2O, PO and PO2

Author Institution: Department of Chemistry, University of VirginiaOxygen atoms (160 and 180) were reacted with P4 molecules using ozone photolysis and discharge of oxygen as sources, and the products were trapped in solid argon at 12K. The major product $P_{4}O$ exhibited a strong terminal $P=0$ stretching mode at $1241 cm^{-1}$, a $P-P=O$ deformation mode at $243 cm^{-1}$, and four P-P stretching modes near P4 values, all of which characterize a $C_{3v}$ species. Two new molecular species probably arise from energized P40 before relaxation by the matrix: the first absorbed at $1197 cm^{-1}$, photolysed with red light, and is probably $P_{2}O$; the second absorbed at 856 and $553 cm^{-1}$, increased with short wavelength radiation, and is most likely due to the $C_{2v}$ bridge-bonded $P_{4}O$ structural isomer. Higher discharge power gave 0 atoms and vacuum ultraviolet radiation; these conditions favored the bridge-bonded $P_{4}0$ species and the simple oxides PO and $PO_{2}$, which were observed at 1218 and $1319 cm^{-1}$, respectively. The matrix efficiently quenched the large exothermicity $(130 \pm 10 kcal/mole)$ for the $P_{4} + 0$ reaction and allowed the lowest oxide of phosphorus $P_{4}0$ to be trapped for the first time as a molecular species

Accretion on the long-lived continental margin of northeastern Australia

The northern extremity of the late Neoproterozoic-Paleozoic Tasman Orogenic zone exposed in north Queensland forms a narrow belt of tectonised rock assemblages abutting Paleoproterozoic–Mesoproterozoic rocks of the North Australian craton. The craton-orogen contact (Tasman Line) is extensively exposed, a unique circumstance for Australia. Sedimentary protoliths of the cratonic rocks were mainly deposited between 1700–1600 Ma and multiply deformed between 1600–1500 Ma. The Lynd Mylonite Zone, one expression of the Tasman Line, separates rocks of the late Neoproterozoic–Ordovician Thomson Orogen from those of the craton. The succeeding Silurian–Devonian Mossman Orogen is generally faulted against the Thomson Orogen, but in its northern extent it may directly abut the craton along the Palmerville Fault, also an expression of the Tasman Line. These two orogenic systems are dominantly of active margin association and E-stepping but deep seismic imaging indicates that they are extensively underlain by crust of Archean or Paleoproterozoic age. The Tasman Orogenic Zone in its southern part represents a broad tract of crust c. 1,000 km across, added to the cratonic core of Australia in a phase of rapid accretion. In contrast, for its north Queensland development a much smaller volume of new crust was generated, expressing slow accretion. For this region the orogenic system laps extensively onto cratonic crust, a geometry which at least in part reflects overthrusting during episodes of Paleozoic contractional orogenesis. As a consequence of little orogenic accretionary outgrowth of the north Queensland continental margin, three large-scale, successive igneous assemblages of active margin association generated throughout the Paleozoic form largely co-located and overprinting belts with plutonic suites stitching the Tasman Line and extending into the craton

Interactions of Porphyromonas gingivalis with oxyhaemoglobin and deoxyhaemoglobin.

When grown on blood-containing solid media, the anaerobic periodontal pathogen Porphyromonas gingivalis produces a haem pigment, the major component of which is the mu-oxo bishaem of iron protoporphyrin IX [Smalley, Silver, Marsh and Birss (1998) Biochem. J. 331, 681-685]. In this study, mu-oxo bishaem generation by P. gingivalis from oxy- and deoxyhaemoglobin was examined. Bacterial cells were shown to convert oxyhaemoglobin into methaemoglobin, which was degraded progressively, generating a mixture of both monomeric and mu-oxo dimeric iron protoporphyrin IX. The rate of methaemoglobin formation was accelerated in the presence of bacterial cells, but was inhibited by N-ethylmaleimide and tosyl-lysylchloromethylketone. Interaction of cells with deoxyhaemoglobin resulted in formation of an iron(III) haem species (Soret gamma(max), 393 nm), identified as pure mu-oxo bishaem

Computational chemistry using modern electronic structure methods

In this article we provide a concise introduction to modern quantum chemical methods for molecular modeling and the calculation of molecular properties. We show that ab initio methods, which include treatment of electron correlation, lead to calculations of molecular geometries and spectroscopic properties that are very close to experimental data. The required input for an electronic structure calculation is discussed in detail, in particular how atomic orbitals may be represented by Gaussian basis functions and how the molecular geometry can be represented by the Z-matrix method. The results of some calculations on simple molecules are presented, enabling a comparison to be made between three popular methods, with various basis sets, and experimental data