Dating stalagmite from Caverna do Diabo (Devil'S Cave) by TL and EPR techniques

A cylindrical fragment of stalagmite from Caverna do Diabo, State of Sao Paulo, Brazil, has been studied and dated by thermoluminescence and electron paramagnetic resonance techniques. The thermoluminescence glow curves of stalagmite samples and subsequently gamma irradiated, have shown rise of three peaks at 135, 180 and 265 degrees C. From electron paramagnetic resonance spectra of stalagmite was possible to clearly identify three paramagnetic centers in the g = 2.0 region: Centers I, II and III are due to, CO3- and CO33-, respectively. The additive method was applied to calculate the accumulated dose using thermoluminescence peak at 265 degrees C and the electron paramagnetic resonance signal at g = 1.9973 of CO2- radical. The ages of the different slices of stalagmite were determined from the D-ac-values and D-an-value, obtaining an average of 86410 for central slice, 53421 for second slice, 31490 for third slice and 46390 years B.P. for the central region of upper end.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Univ Sao Paulo, Inst Fis, Rua Matao,187 Cidade Univ, BR-05508090 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Dept Ciencias Mar, Rua Doutor Carvalho de Mendonca 144, BR-11070100 Santos, SP, BrazilIPEN CNEN SP, Inst Pesquisas Energet & Nucl, Av Prof Lineu Prestes,2242 Cidade Univ, BR-05508000 Sao Paulo, SP, BrazilUniv Nacl San Agustin, Fac Ciencias Nat & Formales, Escuela Profes Fis, Av Independencia S-N, Arequipa, PeruUniv Sao Paulo, Escola Politecn, Dept Engn Met & Mat, Av Prof Mello Moraes 2463, BR-05508030 Sao Paulo, SP, BrazilDepartamento de Ciências do Mar, Universidade Federal de São Paulo, Rua Doutor Carvalho de Mendonça, 144, 11070-100 Santos, SP, BrazilFAPESP: 2014/03085-0CAPES: BEX-9612130Web of Scienc

Confirmation studies of correlation between TL and ESR of natural calcium fluoride

429-431Thermoluminescence (TL) and electron spin resonance (ESR) studies were carried out on natural calcium fluoride (Chougaonkar M P & Gundu Rao T K, Proc NCLA-2005, 2005). It was speculated from the studies that the first two TL peaks appearing approximately at 115 and 200oC may be related to two distinct O2-(I) and O2-(II) radicals, respectively. To assess the validity of the correlation between two ESR centres and the TL peaks, CaF2 without oxygen impurities were obtained by growing single crystals of natural CaF2 in oxygen free atmosphere. The oxygen contents in the host material were also removed using PbF2 as scavenger during the growth. ESR spectrum and TL glow curves were then recorded to study the effect of removal of oxygen from the lattice. The studies indicate that the addition of PbF2 leads to the removal of precursors of O2- radicals as well as CaO present in the lattice and yields clear transparent crystals. It has also been observed that the glow peaks appearing at 115 and 200oC were drastically reduced indicating the near absence of centres responsible for the TL peaks. ESR studies shows the absence radicals O2- I as well as O2- II, thus confirming that these centres are responsible for the TL peaks

Raman Spectrum of cellulose from cotton

78-80Complete removal of laser-induced fluorescence in cellulosic samples from cotton can be achieved through kiering, bleaching and repeated alkali treatments followed by hydrolysis

Luminescence studies in KMgF₃:Eu,Ag

459-460A new sensitive material KMgF3:Eu,Ag has been developed with double dopants europium (Eu) and silver (Ag) by melting equal molecular proportions of KF and MgF2 along with dopants (0.2 mol % each) in argon atmosphere. Luminescence studies have been carried out in this material to check its possible use in radiation dosimetry applications. Thermoluminescence (TL) studies in this material show that its TL sensitivity is three times that of the existing tissue equivalent material LiF:Mg,Ti (TLD-100), while KMgF3 doped with Eu alone and Ag alone shows sensitivities equal to that of TLD-100. KMgF3:Eu,Ag shows a major TL peak around 240oC unlike TLD-100 which has a complicated glow curve shape. The TL emission spectra of gamma irradiated material show characteristic emission of Eu2+. Compared to KMgF3:Eu, the emission intensity of Eu has been found more in KMgF3:Eu,Ag. Photoluminescence studies show that there is no conversion of Eu2+to Eu3+ on gamma irradiation. Electron spin resonance (ESR) studies have been carried out in this material to check if there is any valance conversion of Eu and Ag. Both the irradiated as well as unirradiated materials show signal for Eu2+ ion and did not show any signal for Ag2+ ion. Hence, in the presence of Ag+ more Eu2+ is entering into the crystal lattice which enhances the luminescence efficiency

Studies of defects in YVO<SUB>4</SUB>:Pb<SUP>2+</SUP>, Eu<SUP>3+</SUP> red phosphor material

Doubly doped YVO4:Pb2+, Eu3+ red phosphor materials with fixed Eu3+ concentration (5 mol%) and varying Pb2+ concentration were prepared via a self-propagating (combustion) synthesis. This consisted of bringing a saturated aqueous solution of the desired metal salts and a suitable organic fuel to the boil, until the mixture ignited and a self-sustaining and rather fast combustion reaction initiated, resulting in dry, amorphous or usually crystalline fine particles of the desired material. The formation of crystalline vanadates was confirmed by X-ray diffraction. A strong emission line at 619 nm due to the 5D0 &#8594; 7F2 transition in the red region was observed. Defects, created by gamma radiation, were studied by means of photoluminescence, thermally stimulated luminescence (TSL) and electron spin resonance. Photoluminescence studies display considerable reduction in emission intensity which appears to arise due to the formation of defect centres after irradiation. The defect centres formed in the present system are tentatively assigned to F+ centres and step annealing measurements suggest a connection between these centres and the TSL glow peak

Defect centre responsible for production of 110 degrees C TL peak in quartz

110 degrees C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO(4) tetrahedron and under irradiation gives rise to [GeO(4)/e(-)](-) electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO(4)/h]degrees or [H(3)O(4)/h]degrees centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 degrees C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g(1) = 2.0004, g(2) = 1.9986 and g(3) = 1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 degrees C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O(-) centre. (C) 2009 Elsevier Ltd. All rights reserved.FAPESPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Publications historiques de l'Académie de Vienne, 1862-1865.

Publications historiques de l'Académie de Vienne, 1862-1865.. In: Bibliothèque de l'école des chartes. 1867, tome 28. pp. 377-388

Luminescence and defect centres in Tb(3+) doped LaMgAl(11)O(19) phosphors

Terbium (Tb) doped LaMgAl(11)O(19) phosphors have been prepared by the combustion of corresponding metal nitrates (oxidizer) and urea (fuel) at furnace temperature as low as 500 C Combustion synthesized powder phosphor was characterized by X-ray diffraction and field emission scanning electron microscopy techniques LaMgAl(11)O(19) doped with trivalent terbium ions emit weakly in blue and orange light region and strongly in green light region when excited by the ultraviolet light of 261 nm Electron Spin Resonance (ESR) studies were carried out to study the defect centres Induced in the phosphor by gamma irradiation and also to identify the defect centres responsible for the thermally stimulated luminescence (TSL) process Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least two defect centres One of the centres (centre I) with principal g-values g(parallel to) = 2 0417 and g(perpendicular to) = 2 0041 is identified as O(2)(-) ion while centre II with an axially symmetric g-tensor with principal values g(parallel to) = 19698 and g(perpendicular to) = 1 9653 is assigned to an F(+) centre (singly ionized oxygen vacancy) An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F(+) centre) seems to originate from an F centre (oxygen vacancy with two electrons) The F centre and also the F+ centre appear to correlate with the observed high temperature TSL peak in LaMgAl(11)O(19) Tb phosphor (C) 2010 Elsevier Masson SAS All rights reservedFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP Brazi

Thermoluminescence, optically stimulated luminescence and ESR studies on LiAl₅O₈:Tb

426-428 The LiAl5O8:Tb phosphor has been prepared by solution combustion synthesis. LiAl5O8:Tb shows two TL peaks at 160 and 330°C, respectively. Continuous Wave OSL (CW-OSL) of LiAl5O8:Tb phosphor is recorded. ESR studies have been carried out to identify defect centres responsible for TL peaks observed in LiAl5O8:Tb. Room temperature ESR spectra of irradiated LiAl5O8:Tb phosphor exhibit two distinct centres. The first ESR line is assigned to a V-centre. The second ESR line is assigned to F+ centre. Both the ESR lines appear to correlate with the 160°C TL peak of LiAl5O8:Tb phosphor. </smarttagtype