Scintillation optical ceramics based on Gd_2O_2S doped with Pr, Tb, or Eu

Abstract

This paper discusses the structural, optical, and spectrokinetic characteristics of ceramics based on gadolinium oxysulfide Gd 2 O 2 S:RE (RE = Pr, Tb, Eu), obtained by the method of uniaxial hot pressing. It is shown that the composition and conditions of hot pressing affect the parameters of the Gd 2 O 2 S lattice and the formation of the predominant grain orientation in the (001) plane of the pinacoid. All the ceramics possess transparency that is high for an anisotropic material (about 40% at a thickness of 1.65 mm) in the intrinsic emission region. The overall x-ray luminescence intensities (relative to CsI:Tl) for the Gd 2 O 2 S:Pr,Ce, Gd 2 O 2 S:Tb(Ce), and Gd 2 O 2 S:Eu ceramics are 50, 160 (120), and 200%, respectively, while the damping time constants are 3.2, 600-700, and 450 µs, respectively.The high density (7.34 g/cm 3 ), relatively small band gap (4.3 eV), and conformity to the requirements on absorption in a wide range of energies of gadolinium oxysulfide (Gd 2 O 2 S), make it promising for use in modern devices of x-ray medical engineering as a matrix for obtaining a scintillation material. Doping this matrix with ions having variable valence, Eu 2+,3+ , Tb 3+,4+ , and Pr 3+,4+ , and possessing a large damping cross section (>10 −14 cm 2 ) ensures a high conversion efficiency of the phosphors, as well as making it possible to vary the spectral composition and radiationdamping time. Powdered phosphors based on Gd 2 O 2 S doped with these elements have been widely used for a long time to record x-ray, UV, and electron radiation, and this explains why their characteristics have been studied fairly deeply. The situation is different for studies of single-crystal and optical polycrystalline-ceramic scintillation materials. There is virtually no information on the former because of problems in obtaining single crystals of Gd 2 O 2 S. As far as ceramic materials are concerned, the scintillation characteristics of Gd 2 O 2 S:Pr,Ce ceramics, which are being actively used in detectors for computerized tomography, have been studied in the greatest detail. 1 This paper presents a review of data based on x-ray structural analysis and the study of the microstructure and transparency of Gd 2 O 2 S:RE ceramics (RE = Pr, Tb, Eu) and obtained by investigating its spectrokinetic characteristics. 2-4 EXPERIMENTAL TECHNIQUEThe process of uniaxial hot pressing (HP) of the samples was carried out in high-temperature vacuum furnaces. The original powders used in this paper, a characteristic image of which is shown in Fig. 1(a), had a grain size of 3-7 µm. The concentration of the dopants (Pr 3+ , Tb 3+ , Eu 3+ ) fluctuated within the limits 0.08-1.0 mass%, and the Ce 3+ concentration was 0.002 mass%. Since Gd 2 O 2 S is a refractory compound (T m ≈ 2250 • C), to achieve high density and transparency of the ceramic, the pressing process was carried out in the presence of an easily melted fluorine-containing additive, which simultaneously served the function of supplying the F − ion needed to obtain the required luminesce...

Increasing the intensity of the glow of the phosphor Gd-=SUB=-2-=/SUB=-O-=SUB=-2-=/SUB=-S : Tb(3-7 mol.%), caused by a change in the distribution of the Tb-=SUP=-3+-=/SUP=- activator over the real crystal lattice

“…The PL 542 nm band has the highest intensity and corresponds to transitions of the 4 f −5d level charges of Tb 3+ ions [14][15][16][17] with excitation energy transfer to their 5 D j -levels. Thereat, the increase of PL band intensity in the green spectrum region > 490 nm is confirmed at Tb 3+ ion concentrations of > 3 mol.% [18] due to an increase in the population of 5 D 4 − 7 F j transitions in relation to 5 D 3 − 7 F j transitions [17]. This effect was found previously [19] for the Y 2 O 2 S : Tb compound, but was not checked for the Gd 2 O 2 S compound.…”

“…The obtained results show that the band gap E g of the Gd 2 O 2 S : Tb compounds decreases with an increase of Tb 3+ ion concentration and is small as compared to the pure matrix 4.3−4.6 eV [26,7]. A band-band charge transition takes place with the participation of phonons, and phonon energy increases with an increase of the Tb 3+ ion concentration from 3 to 5 mol.% and then remains constant up to 7 mol.%.…”

“…The impurity phase is not eliminated by repeated product washing and additional annealing for 6 h at 1200 • C in sulfur vapors. The position of the impurity phase reflections corresponds to the GdOF phase (space group R 3m (166) ICSD 184007), which forms in a concurrent reaction of Gd 2 O 3 with LiF fusing agent in the course of oxide sulfidation, similarly to interaction with NH 4 F [12], as distinct from the conjecture of inclusion of F − ions into the Gd 2 O 2 S matrix lattice [7]. It can be assumed that the TbOF impurity phase forms also at increased concentrations of Tb 3+ ions.…”

“…The latter method eliminates the fire hazard and toxicity of production in factory conditions. However, sulfidation rate in this method is very low due to too high temperatures required for the reaction 1350 • C. Temperature is reduced by the use of fusing agents Na 2 CO 3 , Li 2 CO 3 , Na 3 PO 4 in solid-state reactions [4-6,], including LiF with the concentration of 0.01−0.06 wt.% [7]. In the present paper we have used an integrated method for the deposition of Gd hydroxohydroxide, followed by annealing in air to the Gd 2 O 3 oxide and its sulfidation with sulfur vapors in a dispersed mixture with LiF.…”

Physical and optical studies of Gd2O2S:Eu3+ nanophosphors by microwave irradiation and γ‐irradiation methods

“…Gadolinium oxysulfide (Gd 2 O 2 S) is a well known phosphor material based on its wide band‐gap energy (4.6–4.8 eV), making it favourable for use as a matrix for acquiring luminescent emitting materials . It also has high density (7.34 g·cm −3 ) and refractive index ( n = 2.1–2.3), permitting high light absorption and high energy transfer efficiency for luminescent materials . Gd 2 O 2 S exhibited green luminescence and high efficiency under UV irradiation, cathode rays, and X‐rays that were five times brighter than those of CaWO4 .…”