Developments in Ceramic Materials Research

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72 T. T. Basiev, V. A. Demidenko, K. V. Dykel’skii et al. in a wide energy range and high conversion efficiency. Homovalent substitution in cation sublattice of a matrix for any rare – earth (RE) ions from lanthanide row allows to vary spectral and fluorescence kinetic properties and develop oxysulfide materials for different applications. Rare earth oxysulfides crystallize in trigonal system, space group P3-m1, Z = 1 [34]. Its crystal structure corresponds to the А-R2O3 structural type of cerium subgroup rare earth oxides, with substitution of oxygen by sulfur in the crystallographic position. Cation coordination number is seven, with four atoms of oxygen and three atoms of sulfur. Three oxygen and three sulfur atoms form regular Archimedean antiprism, the oxygen bottom of antiprism is capped by forth oxygen atom. Hexagonal structure of oxysulfides anticipates anisotropy of optical properties of RE ions. In the La, Gd, Y oxysulfide row a minimal value of Δn = ne – no is observed in La2O2S. Moreover, for λ = 0.56 μm Δn is zero in La2O2S [35]. A La, Gd, Y oxysulfides have high melting points – 2000 – 2100C [34]. Together with high reactivity, that is a reason of a lack of high advances in oxysulfide single crystals growth. There are only few papers, which communicate about rather small not of a top quality the La2O2S and Y2O2S single crystals doped with Nd 3+ or Er 3+ [35 - 38]. In this connection methods of synthesis of luminescent optical oxysulfide ceramics are of interest to material science as alternative. One of them that is gaining acceptance in recent years is a hot- pressing of micro- and, especially, nanopowder precursor. As a result, the Gd2O2S: Pr, Ce ceramic scintillators are synthesized and profitably employed in X-ray tomography by Hitachi (Japan) [39] and Siemens (Germany) [40]. In Russia, the work towards creating the rare-earth oxysulfide based luminescent optical ceramics is carried out at FGUP NITIOM VNC “S.I. Vavilov GOI”. The Y2O2S and La2O2S based transparent ceramics doped with a variety of impurities has been obtained [41 - 43]. In 1999 – 2003 the Gd2O2S:Pr,Ce and Gd2O2S:Tb,Ce optical ceramics is developed that offeres scintillation characteristics being on a par with the world best samples, but unlike the latter features quite high transparency in the visible and IR in spite of anisotropy [44 - 47] (Figure 18). Figure 18 (Continued).
Optical Fluoride and Oxysulfide Ceramics: Preparation and Characterization 73 Figure 18. Fluorescence spectra (a), total transmission spectrum (b), and microstructure (c) of the Gd2O 2S-Pr,Ce (1) and Gd 2O 2S -Tb,Ce (2) ceramic samples. The research carried out allows to assign that the Gd2O2S - Pr, Ce and Gd2O2S:Tb, Ce ceramics obtained features high transparency for its own emission for 1.65 mm thick sample. Its x-ray luminescence intensity commensurate with that of their powder counterparts and reveals fast luminescence damping after 500 ms - I/I0 = 0.001-0.002% and 0.004% for Gd2O2S - Pr, Ce and Gd2O2S:Tb, Ce, respectively. This part of the chapter summarizes the results of study of the Gd2O2S: Nd 3+ and La2O2S: Nd 3+ ceramics. The technique for preparation of oxysulfide ceramics is similar to that for fluoride ceramics. The raw materials used are the Gd2O2S: Nd 3+ and La2O2S: Nd 3+ powders of 3 - 5 μm particle size. The powders featured a uniform grain composition with the predominantly isometric shape of grain (Figure 19). In order to obtain a high density and transparency of the ceramics, the hot pressing process is provided in presence of fusible LiF additive. The introduction of LiF speeds up the densification process significantly and raises the degree of densification of powder oxysulfides. Employing liquid phase mechanisms in the densification process due to the fusible compound promotes the slip at grain borders, intensifies the mass transfer due to diffusion and recrystallization processes. This all allows to obtain the ceramics of x-ray structural density and high transparency. The Nd 3+ concentration in Gd2O2S is 0.1 and 0.5 wt. %, and in La2O2S - 1.0 wt. %. The samples after hot pressing appear as 35 mm disks in diameter and up to 2 mm thick. The density of ceramics corresponds to more than 0.99 of x-ray structural ceramics. The lattice parameters in ceramic samples are measured on a diffractometer with copper anode and nickel filter, and are determined with a reference to a system of crystallographic planes (312) and (205) at large reflection angles (112 0 - 120 0 ). The measured parameters for the Gd2O2S: Nd 3+ samples (0.1-0.5 wt. %) are a = 3.854 ± 0.001 Å, с= 6.670 ± 0.002 Å, for the La2O2S: Nd ceramics (1.0 wt. %) – a = 4.051 ± 0.001 Å, с = 6.942 ± 0.002 Å.
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DEVELOPMENTS IN CERAMIC MATERIALS R
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Copyright © 2007 by Nova Science P
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PREFACE Ceramics are refractory, in
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Preface ix crystals is discussed. A
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Preface xi spectra and the directio
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2 Leslie G. Cecil comprehensive dat
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4 Leslie G. Cecil Ringle et al. (19
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6 Leslie G. Cecil The main architec
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8 Leslie G. Cecil can study “the
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10 Leslie G. Cecil Middleton et al.
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12 Leslie G. Cecil The laser ablate
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14 Leslie G. Cecil There are two ge
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16 Leslie G. Cecil distinct recipes
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18 Leslie G. Cecil second group (Fi
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20 Leslie G. Cecil The Vitzil-Orang
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Page 50 and 51: 36 Z. C. Li, Z. J. Pei and C. Tread
Page 68 and 69: 54 T. T. Basiev, V. A. Demidenko, K
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Sm (J/Kmol) Sm (J/Kmol) 15 10 5 Syn
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Synthesis, Spectroscopic and Magnet
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The Use of Ceramic Pots in Old Wors
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3.2. Wall-in Positions The Use of C
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IACC ( τ ) = t2 ∫ The Use of Cer
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where σ res is the scattering cros
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D50 0.8 0.7 0.6 0.5 0.4 0.3 The Use
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Definition (D50) 1 0.95 0.9 0.85 0.
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Modeling of Thermal Transport in Ce
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q x = Modeling of Thermal Transport
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212 R. Ramesh, H. Kara, Ron Stevens
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220 ε S 33 R. Ramesh, H. Kara, Ron
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242 Development of Display Technolo
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244 Li Chen technology moved to the
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246 Li Chen The continuing evolutio
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248 Li Chen the back contact cathod
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250 Li Chen Figure 3. Vertical side
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252 Li Chen Figure 6. Molybdenum mi
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254 Li Chen Figure 8(a). I-V curve
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256 Li Chen Figure 9. Life time tes
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258 Figure 11(a). Plasma generated
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260 Li Chen [13] C.A. Spindt, K.R.
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262 S. Ardizzone, C. L. Bianchi, G.
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A absorption spectra, 66, 67, 77, 7
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correlation function, 156 corrosion
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group membership, 13, 20, 21, 22, 2
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microstructure(s), x, xi, 73, 74, 2
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efraction index, 61 refractive inde
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time, vii, ix, 1, 3, 7, 8, 11, 26,
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