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Title: Spectroscopy and energy transfer in metal ion doped complexes
Other Titles: Shan za jin shu li zi fu [i.e. fu] he wu de guang pu yu neng liang chuan di
Authors: Jia, Guohua (夾國華)
Department: Department of Biology and Chemistry
Degree: Doctor of Philosophy
Issue Date: 2009
Publisher: City University of Hong Kong
Subjects: Rare earth metals -- Spectra.
Metal ions -- Spectra.
Spectrum analysis.
Energy transfer.
Notes: CityU Call Number: QC462.R2 J53 2009
xxi, 231 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2009.
Includes bibliographical references (leaves 192-231)
Type: thesis
Abstract: This thesis had two major aims. The first one was to select some laser crystals and investigate the spectra and energy transfer processes between ions doped into these crystals. The dopant ions were lanthanide ions or lanthanide-transition metal pairs. The host crystals were YBO3, Y3Al5O12, KPb2Cl5 and NaYF4, so that both oxide and halide systems were investigated. The second aim was to relate the optical spectra to the structure of lanthanide complexes. The two types of system chosen were structural and optical isomeric complexes. A variety of metal ion doped systems in types of halide (fluoride and chloride), oxide, and organic complexes have been prepared and subjected to spectroscopic investigation from 10 K to room temperature. To investigate the spectra and energy transfer processes, certain wavelengths were selected for excitation into the absorption bands of the host lattice or ligand, in addition to charge transfer band, 4fn → 4fn-15d1 and 4fn → 4fn excitations. The following describes these types of system briefly. 1. Halide (fluoride and chloride) systems. A. Hexagonal and cubic NaYF4 were selectively synthesized with the control of preparation conditions. Two pairs of ions including Mn2+-Yb3+ and Eu3+-UO22+ were incorporated into hexagonal NaYF4 to investigate energy transfer processes between these ions. No upconversion emission of Mn2+ was observed with the excitation into the absorption transition 2F7/2 → 2F5/2 of Yb3+ ions whereas selective excitation into the absorption bands of UO22+ can lead to the emission of Eu3+, which can be attributed to a phonon-assisted energy transfer process from the first excited state of UO22+. B. Using synchrotron radiation to excite into the conduction band of KPb2Cl5 singly doped with Er3+, Nd3+, or Pr3+, all of these systems gave broad bands associated with the emissions of Pb2+ with sharp 4f-4f transitions superimposed on the broad bands only in the case of KPb2Cl5:Er3+. The vacuum ultraviolet, ultraviolet and visible spectra of KPb2Cl5:Er3+ have been investigated and interpreted. 2. Oxide systems. A. The effects of doping vanadate ions into YAG upon the luminescence of the lanthanide ions Eu3+ and Pr3+ have been investigated. The vanadate chromophore acts a super antenna for Eu3+ so that even trace impurities exhibit luminescence. However, Pr3+, unlike Eu3+, has a propensity to form tetrapositive ions. The presence of vanadate quenches Pr3+ emission from the 3P0 state by charge transfer. B. The spectroscopic properties of the orange emission from Y1-xGdxBO3:Eu3+ and green emission from Y1-xGdxBO3:Tb3+ phosphors were investigated. The site symmetry of Eu3+ in the YBO3 pseudo-vaterite host was analyzed in detail and the role of the incorporation of Gd3+ into the orthoborates on the emission intensities of Eu3+ and Tb3+ was discussed. 3. Organic complexes. Two types of organic-lanthanide complexes, structural isomers and optical isomers, have been prepared and subjected to crystallographic, FT-IR, Raman vibrational and electronic emission spectra investigations. Contrary to the previously-published X-ray data, where geometrical differences were stated to occur for certain enantiomers, the vibrational (and the emission) spectra of the individual optical isomers of this particular complex were not distinguishable. The organic-lanthanide complexes with nicotinate and isonicotinate ligands show different structures and geometries and therefore the obtained electronic emission spectra are different. Fittings of 25 4f6 crystal field energy levels of the isomeric complexes have been attempted with some approximations concerning the local Eu3+ environments, and the crystal field strengths of Eu3+ in these complexes were calculated.
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