Synthesis, thermoluminescence, defect center and dosimetric characteristics of LiF:Mg,Cu,P,Si phosphor.

LiF:Mg,Cu,P,Si (MCPS), a new tissue equivalent phosphor, was synthesized by solid state method. Powder x-ray diffraction and scanning electron microscope were employed to determine the structural features. The dosimetric characteristics, electron spin resonance (ESR) and defect centers of this newly prepared phosphor were investigated. The MCPS phosphor is highly sensitive when compared with LiF:Mg,Ti and LiF:Mg,Cu,P (MCP), with the TL sensitivity being 35 times and 1.3 times higher respectively. The dosimetric peak occurs at 220°C with a well defined glow curve structure similar to MCP. MCPS phosphor shows a linear dose response till 10Gy. The minimum detectable dose has been found to be 8µGy. The thermal stability of the phosphor could be enhanced by 20°C from 240°C to 260°C when compared to MCP. Defect centers formed in the phosphor by gamma irradiation have been studied by ESR to identify the centers associated with the TL process in this phosphor. Thermal annealing experiments reveal the presence of several defect centers. Center I which shows an isotropic g factor of 2.0233 has been found to relate with the TL peaks at 160°C, 220°C and 265°C. Centers II and III are characterized by isotropic g values of 2.0096 and 2.0019 respectively and are attributed to F centers.

Synthesis, thermoluminescence, defect centers and dosimetric characteristics of LiF:Mg,Cu,B phosphor.

The present paper reports the thermoluminescence (TL), dosimetric characteristics and electron spin resonance (ESR) of LiF: Mg, Cu,B (MCB) phosphor synthesized by a solid state method. Its glow curve structure is similar to that of LiF: Mg, Cu,P (MCP) phosphor with the main dosimetric peak at 218°C. MCB is 12 times more sensitive than LiF: Mg, Ti and about 1.9 times less sensitive than MCP phosphor. A noteworthy feature is that the phosphor exhibits a linear dose response up to 100Gy with a minimum detectable dose of 17µGy. The TL emission spectrum was recorded and the post irradiation fading in MCB at ambient temperatures and humidity was negligible for a period of one month. Room temperature ESR spectrum of irradiated phosphor consists of at least two distinct centers. Center I with an isotropic g factor 2.0061 is attributable to an F-center and is the likely recombination center for the main TL peak at 220°C. Center II characterized by a g-factor 2.0090 and an unusual broad line (linewidth ~ 415G) is also identified as an F-center. A third defect center, observable during thermal annealing at high temperature, is assigned to another F-center.

Hydrothermal Synthesis and Characterization of a Novel Two-Dimensional Tellurite of Molybdenum(VI), (NH(4))(6)Mo(8)Te(8)O(43).H(2)O.

A novel, two-dimensional tellurite of molybdenum(VI), (NH(4))(6)Mo(8)Te(8)O(43).H(2)O, has been isolated as single crystals in a hydrothermal reaction and characterized by single-crystal X-ray diffraction, infrared spectroscopy, and thermal analysis. Pertinent crystal data are as follows: trigonal space group P&thremacr;, a = 12.124(4) Å, c = 8.130(3) Å, Z = 1. Its strucrure consists of (Mo(8)Te(8)O(43))(6)(-) layers interleaved with ammonium ions. The novel feature of the anionic layer is that it contains two anions, discrete [Mo(2)O(7)](2)(-) anions residing in an extended framework of (Mo(6)Te(8)O(36))(4)(-) anions made by corner connection of edge-shared bi-octahedral Mo(2)O(10) units, TeO(3) pyramids, and TeO(4) units with SF(4) geometry. Its decomposition temperature is 371 degrees C.

Low-Temperature Syntheses and Characterization of Novel Layered Tellurites, A(2)Mo(3)TeO(12) (A = NH(4), Cs), and "Zero-Dimensional" Tellurites, A(4)Mo(6)Te(2)O(24).6H(2)O (A = Rb, K).

Hydrothermal synthetic investigations to prepare new A(2)Mo(3)TeO(12) (A = NH(4), Cs, Rb, K) compounds are described. Novel noncentrosymmetric layered tellurites, (NH(4))(2)Mo(3)TeO(12) (1) and Cs(2)Mo(3)TeO(12) (2), have been synthesized by hydrothermal methods. Their structures contain two-dimensional hexagonal tungsten oxide related (Mo(3)TeO(12))(2)(-) anionic layers interleaved with NH(4)(+)/Cs(+) ions. New "zero-dimensional" tellurites, Rb(4)Mo(6)Te(2)O(24).6H(2)O (3) and K(4)Mo(6)Te(2)O(24).6H(2)O (4), containing discrete centrosymmetric (Mo(6)Te(2)O(24))(4)(-) anionic aggregates and alkali metal ions have been synthesized by simple refluxing of stoichiometric reactants in water. In this hexamolybdoditellurite anion, the Mo(6)O(24) flat hexagonal ring, formed from edge sharing of six MoO(6) octahedra, is capped by tellurium on both sides. The two types of anions have the same empirical formula. Cs(2)Mo(3)TeO(12) (2) could be prepared by a solid state reaction as well. All four new tellurites have been structurally characterized by single-crystal X-ray diffraction studies. Pertinent crystal, data are as follows: for 1, hexagonal space group P6(3), a = 7.332(2) Å, c = 12.028(4) Å, Z = 2; for 2, hexagonal space group P6(3), a = 7.3956(10) Å, c = 12.186(2) Å, Z = 2; for 3, monoclinic space group P2(1)/c, a = 10.0564(14) Å, b = 9.877(8) Å, c = 15.724(3) Å, beta = 109.988(11) degrees, Z = 2; for 4, monoclinic space group P2(1)/c, a = 9.878(3) Å, b = 9.724(4) Å, c = 15.301(3) Å, beta = 108.57(2) degrees, Z = 2. Low-temperature syntheses, structure, and powder X-ray diffraction, spectroscopic, and thermal studies of compounds 1-4 are described.

Hydrothermal synthesis and characterization of new pillared layered ethylenediphosphonates of molybdenum(VI), A2[Mo2O5(O3PCH2CH2PO3)] (A = NH4, Tl, Cs, Rb) and K(H3O)[Mo2O5(O3PCH2CH2PO3)].

New ethylenediphosphonates of molybdenum, A[Mo2O5(O3PCH2CH2PO3)] (A = NH4 (1), Tl (2), Cs (3), Rb (4)), and K(H3O)[Mo2O5(O3PCH2CH2PO3)] (5), have been synthesized by a hydrothermal method and structurally characterized by X-ray diffraction, spectroscopic, and thermal studies. These compounds consist of pillared anionic layers [Mo2O5(O3PCH2CH2PO3)]2-, with A+, K+, and H3O+ ions in the interlayer region as well as in the cavities within the anionic layers. Single-crystal X-ray structures of compounds 1 and 5 have been determined. They crystallize in the orthorhombic space group Cmca with Z = 8 and have the following unit cell parameters. For 1, a = 25.60(1), b = 10.016(4), and c = 9.635(3) angstroms and for 5, a = 25.63(1), b = 10.007(2), and c = 9.512(1) angstroms.