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High pressure luminescence studies of europium doped GaN

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Journal of Rare Earths 2009年第4期27卷 667-670页

作者： K.wisniewski w.Jadwisieńczak T.Thomas M.spencer Institute of of Experimental Physics Gdańsk University ul.Wita Stwosza 57 Gdańsk 80-952 Poland School of Electrical Engineering and Computer Science Ohio-University Athens OH 45701 USA Second of Electrical and Computer Engineering Cornell University Ithaca NY 14853 USA

we reported on the high pressure luminescence spectra of polycrystalline Eu-doped GaN material synthesized in the reaction between alloys of gallium, bismuth and europium in ammonia atmosphere. The integrated luminescence intensity of the dominant Eu3＋ ion transition （5D0→^7F2） at 622 nm increased approximately one order of rnagnitude whereas its spectral position and line width did not change significantly between ambient and 6.8 GPa pressure, respectively. Moreover, material was characterized with photo- and cathodo-luminescence, and photoluminescence excitation spectra at different temperatures. It was found that the Eu3＋ ions occupying substitutional Ga site created different centers which could be effectively excited with above band gap excitation and from excitons resonantly photoexcited at the I2 bound exciton energy. Furthermore, the less efficient Eu3＋ ions excitation path existed through intrinsic impurities and defeels generating shallow energy levels in the forbidden gap. It was proposed that reduction of the thermal quenching and consequent enhancement of Eu3＋ ion emission intensity resulted from stronger localization of bound exciton on RESI trap induced by applied pressure.

关键词： GaN, Eu^3+ ion high pressure spectroscopy rate earths

Permian–Triassic Charophytes: Distribution, Biostratigraphy and Biotic Events

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Journal of Earth Science 2018年第4期29卷 778-793页

作者： spencer G Lucas New Mexico Museum of Natural History 1801 Mountain Road N. W. Albuquerque New Mexico 87104 USA

Permian charophytes are known from the Ukraine, Russia, Kazakhstan, Germany, Saudi Arabia, China, the USA, Brazil, Paraguay and India. Most of these records are of Middle- Late Permian Age and are the basis of local biostratigraphic zonation in southern Russia and China. Development of a robust Permian charophyte biostratigraphy will require a more extensive record. Triassic charopbytes are known from Germany, Sweden, Poland, Slovenia, Bulgaria, the Ukraine, Russia, Morocco, Congo, the USA, Argentina, Kazakhstan and China. This encompasses records from all Triassic stages and has been the basis of detailed biostratigraphic zonation in southern Russia-Kazakhstan-eastern Europe. Permian and Triassic charophyte biostratigraphy at the level of genus does not provide detailed correlations beyond local or regional schemes. Nevertheless, it does identify some important evolutionary datums that constrain the timing of important biotic events in the Permian-Triassic evolutionary history of the Charophyta, including：（1） Early Permian extinction of the Palaeocharaceae; （2） Late Permian extinction of the ＂Trochiliscales＂（Moellerinales）; （3） Carboniferous origin of the paraphyletic Porocharaceae, soon followed during the Permian by the origin of the multicellular basal plate; and （4） an important generic turnover of charophytes across the Triassic-Jurassic boundary, though there are insufficient data to identify this as a mass extinction.

关键词： Permian Triassic charophytes biostratigraphy biotic events.

"Miles wide and miles deep"-Exploring the depth and breadth of geoscience during the first ten years of Geoscience Frontiers

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Geoscience Frontiers 2019年第3期10卷 1219-1221页

作者： Christopher J. spencer Nick M.w.Roberts Damian Nance The Institute of Geoscience Research (TIGeR) School of Earth and Planetary Sciences Curtin University NERC Isotope Geosciences Laboratory British Geological Survey Department of Geological Sciences Ohio University Department of Geology and Geophysics Yale University

when early explorers first crossed the Platte River in what is now Nebraska (USA), it was said the river was “a mile wide and an inch deep”(Mokler, 1923;Smith, 1971). This phrase was used to describe not only the difficulty in crossing the river but also in navigating its length. The trouble with a river being too wide is the risk that it won’t provide the depth necessary to be useful. The same thing can be said of multidisciplinary scientific journals. while a journal can claim to be multidisciplinary, there is a risk of it being so broad that its articles can only engage the reader at a superficial level. Nothing could be further from the truth with Geoscience Frontiers. Over the past ten years, this journal has successfully navigated the wide breadth of geoscience while providing a level of depth and detail that rivals discipline-specific journals.

关键词： engage its was can past be is now

The effect of volume change and stack pressure on solid-state battery cathodes

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SusMat 2023年第5期3卷 721-728页

作者： Boyang Liu Shengda DPu Christopher Doerrer Dominic spencer jolly Robert A.House Dominic L.R.Melvin Paul Adamson Patrick S.Grant Xiangwen Gao Peter G.Bruce Department of Materials University of OxfordOxfordUK The Faraday Institution DidcotUK The Henry Royce Institute University of OxfordOxfordUK Future Battery Research Center Global Institute of Future TechnologyShanghai Jiao Tong UniversityShanghaiChina Department of Chemistry University of OxfordOxfordUK

Solid-state lithium batteries may provide increased energy density and improved safety compared with Li-ion ***,in a solid-state composite cathode,mechanical degradation due to repeated cathode volume changes during cycling may occur,whichmay be partially mitigated by applying a significant,but often impractical,uniaxial stack ***,we compare the behavior of composite electrodes based on Li4Ti5O12(LTO)(negligible volume change)and Nb2O5(+4%expansion)cycled at different stack *** initial LTO capacity and retention are not affected by pressure but for Nb2O5,they are significantly lower when a stack pressure ofw volumechange cathode materials or a proper buffer layer are required for solid-state batteries,especially at low stack pressures.

关键词： cathode interface mechanical degradation stack pressure solid-state battery

Regional trends and petrologic factors inhibit global interpretations of zircon trace element compositions

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Geoscience Frontiers 2024年第5期15卷 300-307页

作者： Nick M.w.Roberts Christopher J.spencer Stephen Puetz C.Brenhin Keller Simon Tapster Geochronology and Tracers Facility British Geological SurveyNottingham NG125GGUK Department of Geological Sciences and Geological Engineering Queen’s UniversityKingstonOntarioCanada 475 Atkinson Dr Suite 704HonoluluHI 96814USA Department of Earth Sciences Dartmouth CollegeHanoverNew HamphireUSA

The trace element composition of zircon reveals information about the melt that they are derived from,as such,detrital zircon trace element compositions can be used to interrogate melt compositions,and thus the evolution of the continental crust in time and ***,we present a global database of detrital zircon compositions and use it to test whether average global trends for five common petrogenetic proxies truly represent secular changes in continental *** demonstrate that the secular trend is broadly comparable across continental regions for Ti-in-zircon temperatures,but for other trace element ratios interrogated,secular trends are highly variable between continental *** trace element ratios result from multiple petrologic variables,we argue that these petrogenetic proxies can be overinterpreted if projected to global geologic *** particular,we caution against the interpretation of crustal thickness from trace elements in zircon,and we argue that our results negate current hypotheses concerning secular changes in crustal thickness.

关键词： Detrital zircon Trace elements Secular change Eu anomaly Crustal thickness

Strategies towards robust interpretations of in situ zircon Lu-Hf isotope analyses

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Geoscience Frontiers 2020年第3期11卷 843-853页

作者： C.J.spencer C.L.Kirkland N.M.w.Roberts N.J.Evans J.Liebmann School of Earth and Planetary Sciences The Institute for Geoscience Research(TIGeR)Curtin UniversityPerthAustralia Department of Geological Sciences and Geological Engineering Queen’s UniversityKingstonCanada Centre for Exploration Targeting-Curtin Node The Institute for Geoscience ResearchSchool of Earth and Planetary SciencesCurtin UniversityPerthAustrali Geochronology and Tracers Facility British Geological SurveyNottinghamUK John de Laeter Centre GeoHistory Facility School of Earth and Planetary SciencesCurtin UniversityPerthAustralia

The combination of U-Pb and Lu-Hf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon *** U-Pb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir(*** mantle) versus an unradiogenic reservoir(*** continental crust),or some mixture of these *** ease of generating large quantities of zircon U-Pb and Lu-Hf data has been in large part facilitated by instrument ***,the dramatic increase in time constrained zircon Lu-Hf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows,onto which robust geological interpretations may be *** this work,we discuss the fundamentals of Lu-Hf isotopes in zircon,which then allows us to provide a robust,accessible,methodology for the assessment of data ***,we discuss some novel techniques for:data visualization—that facilitates better transparency of data interpretation;integration of geographic information—that may reveal spatial trends where temporal trends were only apparent before;and some novel statistical evaluation tools—that may provide more rigorous interand intra-sample comparisons.

关键词： Zircon Geochronology Isotope geochemistry Lu-Hf isotopes Geostatistics Data visualization

Paleosols of the upper Paleozoic Sangre de Cristo Formation,north-central New Mexico:Record of early Permian palaeoclimate in tropical Pangaea

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Journal of Palaeogeography 2017年第2期6卷 144-161页

作者： Lawrence H. Tanner spencer G. Lucas Department of Biological Sciences Le Moyne CollegeSyracuseNY 13214USA New Mexico Museum of Natural History 1801 Mountain Road N.W.AlbuquerqueNM 87014USA

The lower Permian(wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial ***,mudstones display a variety of pedogenic *** mudstone fabrics vary from platy to prismatic;some beds display prominent pedogenic ***-colored root traces are common throughout the section,as are calcareous nodules,which vary from small bodies with diffuse boundaries to vertically stacked,discrete,cm-scale nodules(rhizocretions),and less commonly form coalescing *** occur only in the lower portion of the ca.90-m measured *** of the mudstone beds contain calcretes that are immature(calcic Protosols to calcic Argillisols),but the lower to middle portion of the section also contains mature calcrete horizons(argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces,are of laterally variable thickness and grade to nodular *** are interpreted as floodplain pond carbonates that have undergone pedogenic alteration(palustrine limestones),indicating long periods of exposure under strongly seasonal climatic *** isotopic composition of the pedogenic carbonate displays a substantial range of values,but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate(both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking(palustrine carbonate).During the early Permian,northern New Mexico was situated in a near equatorial position(ca.4° N).The overall character of the paleosols suggests a persistent warm,semi-humid,seasonal climate throughout most of the interval of deposition during the wolfcampian,but with episodically increased aridity during formation of the more mature *** long-term trend of climate change is evident in the stratigraphic section examined for this study.

关键词： Sangre de Cristo Formation wolfcampian Vertisol Argillisol Calcisol Protosol

The replication crisis and its relevance to Earth Science studies:Case studies and recommendations

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Geoscience Frontiers 2024年第4期15卷 304-314页

作者： Stephen J.Puetz Kent C.Condie Kurt Sundell Nick M.w.Roberts Christopher J.spencer Slah Boulila Qiuming Cheng 475 Atkinson Dr Suite 704HonoluluHI 96814USA New Mexico Institute of Mining and Technology SocorroNM 87801USA Idaho State University PocatelloID 83209USA Geochronology and Tracers Facility British Geological SurveyKeyworthNottingham NG125GGUK Queen’s University Department of Geological Sciences and Geological EngineeringKingstonOntario K7L 3N6Canada Sorbonne Université CNRSInstitut des Sciences de la Terre ParisParisFrance State Key Laboratory of Geological Processes and Mineral Resources China University of GeosciencesWuhan 430074China

Numerous scientific fields are facing a replication crisis,where the results of a study often cannot be replicated when a new study uses independent *** issue has been particularly emphasized in psychology,health,and medicine,as incorrect results in these fields could have serious consequences,where lives might be at *** other fields have also highlighted significant replication problems,the Earth Sciences seem to be an *** paucity of Earth Science research aimed at understanding the replication crisis prompted this ***,this work aims to fill that gap by seeking to replicate geological results involving various types of *** identify and discuss 11 key variables for replicating U-Pb age distributions:independent data,global sampling,proxy data,data quality,disproportionate non-random sampling,stratigraphic bias,potential filtering bias,accuracy and precision,correlating time-series segments,testing assumptions and divergent analytical methods,and analytical *** while this work primarily focuses on U-Pb age distributions,most of these factors(or variations of them)also apply to other geoscience ***,some of the discussions involve time-series consisting ofεHf,δ18O-zircon,14C,10Be,marineδ13C,and marineδ*** then provide specific recommendations for minimizing adverse effects related to these factors,and in the process enhancing prospects for replicating geological results.

关键词： Replication crisis Replicability Independent data Global time-series Globality index Filtered data

Deconvolving the pre-Himalayan Indian margin-Tales of crustal growth and destruction

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Geoscience Frontiers 2019年第3期10卷 863-872页

作者： Christopher J.spencer Brendan Dyck Catherine M.Mottram Nick M.w.Roberts wei-Hua Yao Erin L.Martin Earth Dynamics Research Group The Institute for Geoscience Research (TIGeR) Department of Applied Geology Curtin University NERC Isotope Geosciences Laboratory British Geological Survey Department of Earth Sciences Simon Fraser University University Drive Department of Environment Earth and Ecosystems The Open UniversityWalton Hall Milton Keynes MK7 6AA UK School of Earth and Environmental Sciences University of Portsmouth Schoolof Earth Sciences and Engineering SunYat-sen University

The metamorphic core of the Himalaya is composed of Indian cratonic rocks with two distinct crustal affinities that are defined by radiogenic isotopic geochemistry and detrital zircon age spectra. One is derived predominantly from the Paleoproterozoic and Archean rocks of the Indian cratonic interior and is either represented as metamorphosed sedimentary rocks of the Lesser Himalayan Sequence(LHS) or as slices of the distal cratonic margin. The other is the Greater Himalayan Sequence(GHS) whose provenance is less clear and has an enigmatic affinity. Here we present new detrital zircon Hf analyses from LHS and GHS samples spanning over 1000 km along the orogen that respectively show a striking similarity in age spectra and Hf isotope ratios. within the GHS, the zircon age populations at 2800-2500 Ma,1800 Ma, 1000 Ma and 500 Ma can be ascribed to various Gondwanan source regions; however, a pervasive and dominant Tonianage population(～860-800 Ma) with a variably enriched radiogenic Hf isotope signature(eHf = 10 to-20) has not been identified from Gondwana or peripheral accreted terranes. we suggest this detrital zircon age population was derived from a crustal province that was subsequently removed by tectonic erosion. Substantial geologic evidence exists from previous studies across the Himalaya supporting the Cambro-Ordovician Kurgiakh Orogeny. we propose the tectonic removal of Tonian lithosphere occurred prior to or during this Cambro-Ordovician episode of orogenesis in a similar scenario as is seen in the modern Andean and Indonesian orogenies, wherein tectonic processes have removed significant portions of the continental lithosphere in a relatively short amount of time. This model described herein of the pre-Himalayan northern margin of Greater India highlights the paucity of the geologic record associated with the growth of continental crust. Although the continental crust is the archive of Earth history, it is vital to recognize the ways in which preservation

关键词： Himalaya Gondwana Zircon Subduction erosion