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      Optical properties of rare-earth doped fluorozirconate glass-ceramics for x-ray detector applications

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      GoOkada_MSc_2010.pdf (2.970Mb)
      Date
      2010-06
      Author
      Okada, Go
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      For high-resolution X-ray imaging scintillator applications, we have prepared and optically characterized divalent samarium doped fluorochlorozirconate (FCZ:Sm2+) glasses and glass-ceramics. Sm2+ doped FCZ glasses were obtained by adding a reducing agent, NaBH4 into the initial melt to convert some of the Sm3+ to Sm2+. However, the Sm2+ concentration at most was estimated to be only approximately 0.003 %. The as-prepared glass samples were further heat treated to obtain glass-ceramics; the nucleation and growth of BaCl2 nanocrystals were confirmed by powdered X-ray diffraction (XRD) experiments. Depending on the heat treatment conditions (temperature and time), the average nanocrystal size varies from 8 to 170 nm, and the sample contains BaCl2 nanocrystals with the orthorhombic and/or hexagonal structure. The optical absorption spectra for our glass-ceramic samples suggested the substitution of Sm2+ ions into the BaCl2 lattice site. The FCZ:Sm2+ glass-ceramics samples showed strong fluorescence in the red region of spectrum (approximately 8 times that of an as-prepared glass), and the transparency can be very high (transmittance > 80 % for samples with thickness about 0.5 mm) and can be equivalent to that of an as-prepared glass . These two results promise potential as a high-resolution X-ray scintillator due to the emission wavelength range and high transparency. Extensive studies of photoluminescence (PL) spectra at low temperatures (12 -- 200 K) for FCZ:Sm2+ glass-ceramics suggested useful indicators of the crystal structure and average size of embedded BaCl2 nanocrystals. A detailed analysis of the optical spectra has lead to the identification of the origin of the emission peaks and the location of Sm ions at specific crystallographic sites. X-ray induced luminescence (XL) studies have suggested a strong dependence of the fluorescence intensity on the concentration of Sm2+ ions. In addition, for more efficient fluorescence, a sample should be heat treated in a hydrogen containing atmosphere (e.g. H2 + Ar gas), and the heat treatment conditions should be such that the nanocrystals grow in the hexagonal structure.
      Degree
      Master of Science (M.Sc.)
      Department
      Electrical Engineering
      Program
      Electrical Engineering
      Supervisor
      Kasap, Safa
      Committee
      Chen, Li; Yang, Qiaoqin; Johanson, Robert
      Copyright Date
      June 2010
      URI
      http://hdl.handle.net/10388/etd-06302010-152011
      Subject
      Glass-Ceramic
      Samarium
      Optical Properties
      X-ray Imaging Scintillator
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