Developments in Ceramic Materials Research

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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).