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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

The study of energy transfer and local field effect in lanthanide complexes with high and low symmetry

Luo, Yuxia 16 August 2019 (has links)
There are lots of important applications for lanthanides (Ln) because of their unique properties. The properties are closely linked to the environment of the crystal field. Thus, two kind of crystals Cs2NaLn(NO2)6 with high Th point-group symmetry and LnPO4 with monoclinic symmetry were chosen to study quantum cutting and Stokes shift. Quantum cutting is a kind of down-conversion energy transfer in which one excitation ultraviolet photon is transformed into multiple near infrared photons. This phenomenon has been studied in Cs2NaY0.96Yb0.04(NO2)6. The emission from Yb3+ can be excited via the NO2- antenna. The electronic transition of NO2- is situated at more than twice the energy of the Yb3+. At room temperature, one photon absorbed at 470 nm in the triplet state produced no more than one photon emitted. Some degree of quantum cutting was observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into singlet and triplet state. The quantum efficiency was about 10% at 25 K. In Chapter 3, Stokes shift which is the energy shift between the peak maxima in absorption and emission was studied. Stokes shift is related to the flexibility of the lattice and the coordination environment. Cs2NaCe(NO2)6 with 12-coordinated Ce3+ situated at a site of Th symmetry demonstrated the largest Ce-O Stokes shift of 8715 cm−1. The 4f1 ground state and 5d1 potential surfaces have displaced so much along the configuration coordinate that overlap takes place above the 5d1 minimum, leading to thermal quenching of emission at 53 K. A comparison of Stokes shifts with other Ce-O systems with different coordination number demonstrated larger Stokes shifts for Ce3+ ions with higher coordination number. Systematic research about the energy transfer (ET) and energy migration phenomenon is still scarce, although they exist extensively among lanthanide ions. The energy migration in highly doped materials has been stated as very fast or slow, but no experimental proof was reported. In Chapter 4, the ET between Tb3+ and Eu3+ was investigated experimentally and compared with available theoretical models in the regime of high Tb3+ concentrations in 30 nm LaPO4 nanoparticles at room temperature. The ET efficiency approached 100% even for lightly Eu3+-doped materials. The use of pulsed laser excitation and switched-off continuous wave laser diode excitation demonstrated that the energy migration between Tb3+ ions, situated on La3+ sites with a 4 Å separation was not fast. The quenching of Tb3+ emission in singly doped LaPO4 only reduced the luminescence lifetime by about 50% in heavily doped samples. Various theoretical models have been applied to simulate the luminescence decays of Tb3+ and Eu3+-doped LaPO4 samples of various concentrations. The transfer mechanism has been identified as forced electric dipole at each ion. The control of energy transfer rate and efficiency is also an important issue. There are many chemical and geometrical factors that affect energy transfer, including the spectra overlap, the dipole orientation and the distance between the donor and acceptor. The local field of the emission center is another factor that affect the energy transfer by changing the photonic environment. In Chapter 5, the local field effect on the energy transfer between Tb3+ and Eu3+ doped in LaPO4 dispersed in different solvents and solids with a wide range of refractive indexes was studied. The effects of local field (reflected by refractive index) on the ET efficiency and ET rates were clarified that the ET efficiency would decrease with increasing refractive index, while ET rates were independent of the refractive index
32

Structure of neutron deficient nuclei near A=140

Kennedy, Gregory Garth. January 1975 (has links)
No description available.
33

Synthesis, characterization, and photophysical studies of organic-lanthanide complexes

Wong, Ka-Leung, 黃嘉良 January 2006 (has links)
published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy
34

Fundamental studies on the separation of the lanthanides using solvent extraction systems

Cecconie, Theodore James, 1961- January 1988 (has links)
Fundamental solvent extraction studies on the separation of the lanthanides were carried out by investigating both the hydroxamic acid and phosphinic acid reagent families. In general, the lanthanides were found to extract as self-adducts. It was found that the separation of the individual lanthanides with both of these reagent families was adversely affected by steric hindrance.
35

Development of water-soluble Ln³⁺-doped LaF₃ nanoparticles as potential biolabels

Diamente, Peter Robert. 10 April 2008 (has links)
No description available.
36

Structural studies on hydrated lanthanide oxalates by ESR spectroscopy.

January 1980 (has links)
by Wong Lai-ping, Gloria. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1980. / Bibliography: leaves 136-140.
37

Reducing rare earth consumption in Nd₂Fe₁₄B magnets through controlled nanostructures

Hopkinson, David Mark January 2015 (has links)
No description available.
38

Synthesis, structural characterization and reactivity of metallacarboranes of lanthanides and early transition metals. / CUHK electronic theses & dissertations collection

January 2005 (has links)
Alkane elimination reaction of Hf(CH2SiMe3) 4 with a zwitterionic salt 1-Me2NHCH2CH2 -1,3-C2B10H12 has resulted in the isolation and structurally characterization of the first example of half-sandwich group 4 metallacarborane alkyls of the C2B10 system. This is also a new route to high-valent group 4 metallacarboranes. / Alkane or amine elimination reactions are also effective methods for the preparation of half-sandwich group 4 metal] acarboranes of the C 2B9 system. The Lewis base functionalized sidearm can effectively stabilize half-sandwich group 4 metallacarborane alkyls through intramolecular coordination. These novel metallacarborane alkyls undergo insertion reaction with alkyne and intramolecular hydrogen atom abstraction reactions. / High-valent group 4 half-sandwich metallacarboranes incorporating an eta 7-carboranyl ligand have been prepared and structurally characterized. The heteroatom-containing pendant sidearms on the carborane cage are both electronically and entropically necessary for the formation of such complexes. / Reaction of [(Me2NCH2CH2)C2B 10H11]Na2 with YCl3 gives eta 1:eta6-[(Me2NCH2CH2)C 2B10H11]YCl(THF)3 containing an exopolyhedral Y-Cl bond, which offers an important intermediate for the preparation of lanthanacarboranes bearing the Ln-C or Ln-X (X = heteroatoms) bonds. On the other hand, it implies that Lewis base functionalized carboranes can stabilize half-sandwich metallacarboranes via the coordination of heteroatom from the sidearm. Silylamine elimination reactions of the neutral ligand 7-Me2NHCH2CH2-7,8-C 2B9H11 with Ln[N(SiHMe2)2] 3(THF)2 are effective method for the preparation of half-sandwich lanthanacarboranes. / Reactions of alkali metal salt of these carboranes with LnCl3 in the presence of excess alkali metal afford a novel class of 13-vertex closo-metallacarboranes incorporating eta7-carboranyl ligands [{eta1:eta1:eta7-[(DCH 2CH2)RC2B10H10]Ln}{Na(solvent) x}]n. Structural studies show that the Lewis base functionalized sidearms have some effects on the coordination environments of the central metal atom, but do not change the gross structures of the 13-vertex closo-metallacarboranes. The reactivity patterns of these 13-vertex closo-metallacarboranes have been studied for the first time. / Several mono- and bisfunctional carboranes (DCH2CH2)RC 2B10H10 (R = H, DCH2CH2, D = MeO, Me2N) have been designed and successfully synthesized. They can be conveniently converted into the monoanions, the dianions and the tetraanions by treatment with suitable reagents. Their applications in organolanthanide and group 4 organometallic chemistry have been studied. / Cheung Mak-shuen. / "June 2005." / Adviser: Kevin W. P. Leung. / Source: Dissertation Abstracts International, Volume: 67-01, Section: B, page: 0258. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 169-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.
39

Soil bioavailability of rare earth elements and their effects on tree growth.

January 2007 (has links)
Wong, Man Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (leaves 173-188). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgements --- p.v / Table of Contents --- p.vii / List of Tables --- p.xi / List of Figures --- p.xiii / List of Plates --- p.xv / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Definition of Rare earth elements --- p.1 / Chapter 1.2 --- Discovery of REEs --- p.5 / Chapter 1.3 --- Physical and chemical properties of REEs --- p.6 / Chapter 1.4 --- Abundance of REEs on earth --- p.10 / Chapter 1.4.1 --- Bastnasite --- p.11 / Chapter 1.4.2 --- Monazite --- p.14 / Chapter 1.4.3 --- Xenotime --- p.16 / Chapter 1.5 --- Reserves and resources --- p.16 / Chapter 1.5.1 --- World reserves --- p.16 / Chapter 1.5.2 --- REE resources in China --- p.18 / Chapter 1.6 --- Production and demand of REEs --- p.20 / Chapter 1.6.1 --- Production and demand in US --- p.21 / Chapter 1.6.2 --- Production and export in China --- p.23 / Chapter 1.6.3 --- Production in other countries --- p.24 / Chapter 1.7 --- Separation of REEs --- p.24 / Chapter 1.7.1 --- Classical methods --- p.24 / Chapter 1.7.2 --- Modern methods --- p.25 / Chapter 1.7.2.1 --- Ion exchange separation --- p.25 / Chapter 1.7.2.2 --- Solvent extraction --- p.25 / Chapter 1.8 --- Applications --- p.26 / Chapter 1.8.1 --- Alloys --- p.26 / Chapter 1.8.2 --- Permanent magnets --- p.28 / Chapter 1.8.3 --- Catalysts --- p.29 / Chapter 1.8.4 --- Glass additives --- p.30 / Chapter 1.8.5 --- Phosphors in television screens and similar fluorescent surfaces --- p.31 / Chapter 1.8.6 --- Fertilizers and feed additives --- p.32 / Chapter 1.9 --- REEs in the environment --- p.33 / Chapter 1.9.1 --- REEs in soil --- p.33 / Chapter 1.9.2 --- REEs in plants --- p.35 / Chapter 1.10 --- Overview of toxicological studies of REEs --- p.36 / Chapter 1.11 --- Current study --- p.38 / Chapter 1.11.1 --- Thesis outline --- p.3 8 / Chapter 1.11.2 --- Objectives --- p.38 / Chapter 1.11.3 --- Significance --- p.39 / Chapter Chapter 2 --- Phytotoxicity of rare earth elements / Chapter 2.1 --- Introduction --- p.41 / Chapter 2.1.1 --- Ecotoxicity of REEs --- p.41 / Chapter 2.1.2 --- Toxicity tests using higher plants --- p.43 / Chapter 2.1.3 --- Advantages of seed germination and root elongation test --- p.44 / Chapter 2.1.4 --- Selection of species --- p.46 / Chapter 2.1.5 --- Endpoint of test --- p.47 / Chapter 2.1.6 --- Median effect estimates --- p.50 / Chapter 2.1.7 --- Objective --- p.50 / Chapter 2.2 --- Materials and methods --- p.50 / Chapter 2.2.1 --- Test species --- p.51 / Chapter 2.2.2 --- Test chemicals --- p.51 / Chapter 2.2.3 --- Range finding test --- p.51 / Chapter 2.2.4 --- Definitive test --- p.52 / Chapter 2.2.5 --- Statistical analyses --- p.52 / Chapter 2.3 --- Results --- p.53 / Chapter 2.3.1 --- Range finding test --- p.53 / Chapter 2.3.2 --- Definitive test --- p.53 / Chapter 2.3.2.1 --- Germination rate --- p.53 / Chapter 2.3.2.2 --- Root length --- p.55 / Chapter 2.3.2.3 --- Germination index --- p.58 / Chapter 2.3.3 --- The median effective concentration --- p.61 / Chapter 2.4 --- Discussion --- p.62 / Chapter 2.4.1 --- Dose-response curves of REEs --- p.62 / Chapter 2.4.2 --- Relative toxicity of the four REEs --- p.63 / Chapter 2.4.3 --- Mechanism of effect of REEs on seed growth --- p.67 / Chapter 2.4.4 --- Comparison between different endpoints --- p.68 / Chapter 2.4.5 --- Comparison between different species --- p.70 / Chapter 2.4.6 --- Limitations and improvement --- p.71 / Chapter 2.4.7 --- Methods of measuring root length --- p.72 / Chapter 2.5 --- Conclusions --- p.73 / Chapter Chapter 3 --- Growth of tree seedlings in soil treated with rare earth elements / Chapter 3.1 --- Introduction --- p.75 / Chapter 3.2 --- Materials and methods --- p.77 / Chapter 3.2.1 --- Soil --- p.77 / Chapter 3.2.2 --- Tree seedlings --- p.77 / Chapter 3.2.3 --- REEs --- p.78 / Chapter 3.2.4 --- Greenhouse experiment --- p.78 / Chapter 3.2.5 --- Soil analysis --- p.80 / Chapter 3.2.5.1 --- Initial properties --- p.80 / Chapter 3.2.5.2 --- Post harvest analysis --- p.81 / Chapter 3.2.6 --- Plant analysis --- p.83 / Chapter 3.2.7 --- Statistical analysis --- p.83 / Chapter 3.3 --- Results --- p.84 / Chapter 3.3.1 --- Growth --- p.84 / Chapter 3.3.1.1 --- Height --- p.84 / Chapter 3.3.1.2 --- Basal diameter --- p.87 / Chapter 3.3.1.3 --- Biomass --- p.89 / Chapter 3.3.1.4 --- Standing leaf number --- p.92 / Chapter 3.3.1.5 --- Chlorophyll fluorescence --- p.95 / Chapter 3.3.2 --- Tissue contents --- p.97 / Chapter 3.3.2.1 --- REEs concentrations --- p.97 / Chapter 3.3.2.2 --- Nitrogen concentrations --- p.99 / Chapter 3.3.2.3 --- Phosphorus concentration --- p.101 / Chapter 3.3.2.4 --- Mineral concentrations --- p.102 / Chapter 3.3.3 --- Soil --- p.104 / Chapter 3.3.3.1 --- Initial properties --- p.104 / Chapter 3.3.3.2 --- REEs concentrations --- p.106 / Chapter 3.3.3.3 --- Nitrogen and phosphorus concentrations --- p.107 / Chapter 3.3.3.4 --- Mineral concentrations --- p.109 / Chapter 3.4 --- Discussion --- p.110 / Chapter 3.4.1 --- Effects of REEs on growth --- p.110 / Chapter 3.4.2 --- Mechanisms of the effect of REEs --- p.112 / Chapter 3.4.3 --- Nutrient uptake --- p.114 / Chapter 3.4.4 --- Soil nutrient contents --- p.116 / Chapter 3.4.5 --- Comparison between REEs --- p.118 / Chapter 3.4.6 --- Comparison between species --- p.121 / Chapter 3.5 --- Conclusions --- p.123 / Chapter Chapter 4 --- Bioavailability and accumulation of rare earth elements / Chapter 4.1 --- Introduction --- p.124 / Chapter 4.2 --- Materials and Methods --- p.126 / Chapter 4.2.1 --- Soil --- p.126 / Chapter 4.2.2 --- Tree seedlings --- p.126 / Chapter 4.2.3 --- Pot experiment --- p.127 / Chapter 4.2.4 --- Chemical speciation of soil --- p.129 / Chapter 4.2.5 --- Statistical analysis --- p.130 / Chapter 4.3 --- Results --- p.130 / Chapter 4.3.1 --- Plant performance --- p.130 / Chapter 4.3.2 --- Tissue contents of La --- p.144 / Chapter 4.3.3 --- Soil --- p.144 / Chapter 4.3.3.1 --- Soil final pH --- p.146 / Chapter 4.3.3.2 --- Soil La contents --- p.146 / Chapter 4.3.4 --- "Association between pH, organic matter and La contents in soil and plant" --- p.149 / Chapter 4.4 --- Discussion --- p.151 / Chapter 4.4.1 --- Growth performance of tree seedling on different soil conditions --- p.151 / Chapter 4.4.2 --- Comparison between growth parameters --- p.152 / Chapter 4.4.3 --- Speciation in soils --- p.154 / Chapter 4.4.4 --- Bioavailability of REEs in soil --- p.155 / Chapter 4.4.5 --- Factors affecting bioavailability of REEs --- p.158 / Chapter 4.4.6 --- Distribution of REEs in plants --- p.162 / Chapter 4.5 --- Conclusions --- p.165 / Chapter Chapter 5 --- General conclusions --- p.167 / Chapter 5.1 --- Summary of major findings --- p.167 / Chapter 5.2 --- Suggestions for further investigation --- p.171 / References --- p.173
40

Rare earth elements distributions and strontium isotope data from the Gem Park igneous complex, Colorado

Roden, Mary Kathleen January 2011 (has links)
Typescript. / Digitized by Kansas Correctional Industries

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