T. Rivera

Preparation of CaSO4:Dy by precipitation method to gamma radiation dosimetry

This paper presents the results of the preparation and characterization of dysprosium-doped calcium sulfate (CaSO(4):Dy) phosphor, which was obtained by homogeneous precipitation from calcium acetate Ca(CH(3)COO(-))(2). Structural and morphological characteristics were studied using a scanning electronic microscope (SEM). The structure of all compounds was determined by X-ray diffraction method too. Thermoluminescence (TL) emission properties of CaSO(4):Dy under gamma radiation effects were studied. This phosphor powder presented a TL glow curve with two peaks (Tmax) centered at around of 180 and 300 degrees C, respectively. The TL response of CaSO(4):Dy as a function of gamma absorbed dose was linear in a wide range. Both emission and excitation spectra were also obtained. Results showed that this new preparation method of CaSO(4):Dy TL phosphor is less expensive, cleaner and safer than the conventional preparation method.

Thermoluminescence (TL) of europium-doped ZrO2 obtained by sol–gel method

This article reports the preparation and characterization of europium-doped zirconium oxide (ZrO2:Eu3+) formed by homogeneous precipitation from propoxyde of zirconium [Zr(OC3H7)4]. The alkoxide sol gel process is an efficient method to prepare the zirconium oxide matrix by the hydrolysis of alkoxide precursors followed by condensation to yield a polymeric oxo-bridged ZrO2 network. All compounds were characterized by thermal analysis and the X-ray diffractometry method. The thermoluminescence (TL) emission properties of ZrO2:Eu3+ under beta radiation effects are studied. The europium-doped sintered zirconia powder presents a TL glow curve with two peaks (Tmax) centered at around 204 and around 292 °C, respectively. TL response of ZrO2:Eu3+ as a function of beta-absorbed dose was linear from 2 Gy up to 90 Gy. The europium ion (Eu3+)-doped ZrO2 was found to be more sensitive to beta radiation than undoped ZrO2 obtained by the same method and presented a little fading of the TL signal compared with undoped zirconium oxide.

Preparation of luminescent nanocrystals started from amorphous zirconia prepared by sol–gel technique

This article reports the experimental results concerning the thermoluminescent (TL) and photoluminescent (PL) characteristics of nanopolicrystalline zirconium oxide (ZrO2) powder prepared by the conventional sol–gel method. Transmission electron miscroscopy and X-ray diffraction techniques were used for morphological and structural characterization of the compound. Thermal annealing processes for the precipitates were studied. It is observed that the crystalline structure and the crystallinity of the powders depend on the annealing temperature. For temperatures higher than 1000 °C, the material presents the monoclinic phase with an average crystalline grain size of 40 nm. The TL glow curve of the undoped ZrO2 has a simple structure with two prominent peaks at around 160 and 270 °C, with a small shoulder in the second peak. TL response of the ZrO2 as a function of beta-irradiation showed a wide range of the dose. Fading and reusability of phosphor were also studied. Measurements on PL show excitation and emission spectra.

Structural characteristics of nanocrystalline ZrO2 powder sol–gel derived to luminescent applications

Interest in nanocrystalline ceramics is increasing nowadays. Sol–gel is a low temperature method, which uses chemical precursors to produce ceramics and glasses with better purity and homogeneity than the conventional high-temperature processes. This new preparation method of nanophosphors has been recently strongly developed for producing high-efficiency luminescent devices. When producing ZrO2 it is important to retain a high degree of crystallization of ZrO2 and its possible correlation with the concentration of defects. The X-ray diffraction patterns of ZrO2 showed that the calcined material has a strongly monoclinic structure. The thermoluminescent glow curve of ZrO2 exhibited two peaks. Photoluminescence spectra of ZrO2 also were obtained.

Thermal and electron stimulated luminescence of natural bones, commercial hydroxyapatite and collagen

The luminescence (cathodoluminescence and thermoluminescence) properties of natural bones (Siberian mammoth and adult elephant), commercial hydroxyapatite and collagen were analyzed. Chemical analyses of the natural bones were determined using by Electron Probe Micro-Analysis (EMPA). Structural, molecular and thermal characteristics were determined by X-ray Diffraction (XRD), Raman spectroscopy and Differential Thermal and Thermogravimetric analysis (DTA-TG). Cathodoluminescence (CL) spectra of natural bones and collagen showed similar intense broad bands at 440 and 490 nm related to luminescence of the tetrahedral anion [Formula: see text] or structural defects. A weaker luminescence exhibited at 310 nm could be attributed to small amount of rare earth elements (REEs). Four luminescent bands at 378, 424, 468 and 576 nm were observed in the commercial hydroxyapatite (HAP). Both natural bones and collagen samples exhibited natural thermoluminescence (NTL) with well-defined glow curves whereas that the induced thermoluminescence (ITL) only appears in the samples of commercial hydroxyapatite and collagen. Additional explanations for the TL anomalous fading of apatite, as a crucial difficulty performing dosimetry and dating, are also considered.

Thermoluminescence sensitivity of daily-use materials †

The thermoluminescence (TL) response of silicon-rich daily-use materials, namely charoite (silicate gemstone), Spanish dental crown, phone chip and Spanish glass has been investigated. All the samples previously characterised by means of X-ray diffraction, electron microscopy associated with energy-dispersion and wavelength-dispersive spectrometry and X-ray fluorescence exhibit a reasonable sensitivity to ionising radiation. The preliminary results, based on their TL properties, allow us to speculate that these materials could be potentially of interest in situations where conventional dosimetric systems are not available. The dose dependence of the 400 nm TL emission of the studied samples displays a very good linearity in the range of 0.1–10 Gy. †Paper presented as a contribution to the 10th International Symposium on Solid State Dosimetry, Mexico City (24–28 September 2007).

Nanostructural processing of advanced thermoluminescent materials

The growing interest in transition ceramic nanoparticles doped with various elements is in constant increasing due to their size-dependent physical properties and its potential applications in thermo-luminescence dosimetry. Zirconium oxide (ZrO2) is a very important semiconductor material having a wide band gap with different interesting applications. Undoped zirconium oxide (ZrO2) and zirconium oxide doped with various elements (ZrO2:VD) have been prepared by thermal treatment of precursor sol–gel glasses. The dependence on annealing temperature and time has been analyzed. The structural analysis of the samples has been made by X-ray diffraction (XRD). The nanocrystals obtained had grain sizes ranging from 8 to 40 nm. Thermally Stimulated Luminescent glow curves were obtained and analyzed.

Thermoluminescent characteristics of synthetic hydroxyapatite (SHAp).

This paper presents the experimental results of the thermoluminescent (TL) characteristics of synthetic hydroxyapatite (SHAp) obtained by the sol-gel method. For preparation of the SHAp powders, phosphorus pentoxide (P2O5) and calcium nitrate tetrahydrated (Ca(NO3)2-4H2O) were used. The powders obtained were submitted at different temperatures. The structural and morphological characterization were carried out using X-ray diffraction (XRD) and scanning electron microscopy techniques. TL glow curve exhibited two peaks centered at around 200 °C and 300 °C. TL response of SHAp as a function of gamma absorbed dose was linear over a wide dose range. Fading of the storage information in the samples irradiated was also studied. The experimental results show that the synthetic hydroxyapatite obtained by the sol-gel method may have used in gamma radiation dosimetry applications.

Luminescent characteristics of CaSO4:Dy films obtained by spray pyrolysis method.

The present paper reports the experimental results of dysprosium doped calcium sulphate (CaSO4:Dy) films deposited by spray pyrolysis method. CaSO4:Dy films were deposited on three different surfaces: glass, aluminum and quartz substrates at temperatures in the range from 450 to 600 °C. Structural and morphological characteristics of CaSO4:Dy films were observed. Thermoluminescent characteristics of films were determined by irradiating ultraviolet energy region. Thermoluminescent glow curve of CaSO4:Dy films with glass and aluminum substrates showed a peak under environmental irradiation. Both TL response glow shape and intensity of CaSO4:Dy films UV irradiated as a function of substrates were studied.

Effect of the chemical impurities on the luminescence emission of natural apatites

This paper reports on both cathodoluminescence (CL) and blue thermoluminescence (TL) emission of well-characterized natural Spanish and Brazilian apatites [Ca5(PO4)3(OH, F, Cl)]. Chemical analyses performed by means of Electron Microprobe Analysis (EMPA) have shown the presence of trace elements that can induce CL bands. In this sense, the apatites shown emission bands peaked at 3.26, 2.86, 2.62, 2.14, 2.02 and 1.94eV are respectively linked to substitutional Ce(3+), Tb(3+), Dy(3+), Pr(3+), Sm(3+) and Mn(2+) in structural Ca(2+) positions. The 3.18eV emission band can be associated with intrinsic electron defects on oxygen of the phosphate group (PO4)(3-). The presence of (UO2)(2+) gives rise to an emission at 2.14eV. All the studied aliquots exhibit one single UV-blue TL peak that modifies the position from one sample to another (370, 256 and 268°C) probably due to (i) the variation in the crystallinity index (from 0.88 to 1.34) and (ii) successive chemical processes such as oxidation, dehydration, dehydroxylation, and fluorine ions losses due to the thermal readout.