Mário E.G. Valerio

Effects of thermal treatment on the TL emission of natural quartz

Abstract In this work we investigated the influence of different thermal treatments on the glow curves and emission spectra of a Brazilian natural crystalline quartz sample. All the thermal treatments were done in air for 1 h at 200–900°C, followed by a fast or a slow cooling down to room temperature. We have shown that sensitization can be achieved without pre-dose and that the main effect is related to the thermal treatment by itself. Samples that were heated to temperatures higher than 200°C and irradiated with the same dose showed a new emission band centered at 370 nm that is responsible for the enhancement of 110°C TL peak. The role played by the [H 3 O 4 ] 0 hole center is discussed. The effect of the cooling down rate was also investigated and it appears to influence the concentration of TL traps.

Yttria thin films doped with rare earth for applications in radiation detectors and thermoluminescent dosimeters

Abstract Thin films of pure and Nd doped Y 2 O 3 were prepared following a new sol–gel route on glass substrate. Sets of thin films were prepared in different oxidation and densification conditions and the effect of such conditions in the morphology, crystallization, surface aspect and thermoluminescence (TL) and radioluminescence response are analysed. The results indicates that the films are suitable for scintillating devices rather than solid state TL dosimeters.

Derivation of potentials for the rare-earth fluorides, and the calculation of lattice and intrinsic defect properties

A detailed reappraisal of the computer modelling of the rare-earth fluorides is presented. A new set of interionic potentials is obtained by empirical fitting to crystal structural data alone. These potentials are then tested by calculation of elastic and dielectric constants, whose values agree favourably with those measured experimentally. Calculations are then presented of the basic defect formation energies for each material, and predictions of the expected type of intrinsic disorder made.

A computational study of intrinsic and extrinsic defects in LiNbO3

Lithium niobate is a material with many important technological applications as a result of its diverse physical properties. Using a recently derived interatomic potential, intrinsic defect energies have been calculated leading to conclusions about the defect properties of the material that are compared with experimental conclusions. The incorporation of dopant ions into the structure is also considered, and solution energies are calculated, which enable predictions to be made about which ions are most easily added and which solution energy schemes are favoured energetically.

Computer modelling of defect structure and rare earth doping in LiCaAlF6 and LiSrAlF6

This paper describes a computational study of the mixed metal fluorides LiCaAlF6 and LiSrAlF6, which have potential technological applications when doped with a range of elements, especially those from the rare earth series. Potentials are derived to represent the structure and properties of the undoped materials, then defect properties are calculated, and finally solution energies for rare earth elements are calculated, enabling preferred dopant sites and charge compensation mechanisms to be predicted.

Influence of co-dopant in the europium reduction in SrAl2O4 host

Xerogels of strontium chlorate and aluminium chlorate doped with europium (un-co-doped) and co-doped with rare earth ions (Ln = Gd, Dy, Er and Y) were prepared using the proteic sol-gel route. Synchrotron radiation was used to investigate the effect of different co-dopants on the Eu(3+) → Eu(2+) reduction process during the synthesis of the samples. Samples were excited at the Eu LIII-edge and the XANES regions were analyzed. The results suggest that some of the Eu ions can be stabilized in the divalent state and that it is difficult to completely reduce Eu(3+) to Eu(2+) during thermal treatment. The mechanisms of the Eu reduction processes are explained by a proposed model based on the incorporation of charge-compensation defects.

A new interatomic potential for the ferroelectric and paraelectric phases of LiNbO3

This paper reports a new interatomic potential for lithium niobate, which has been fitted to the structure and properties of the stoichiometric ferroelectric phase of the material. The potential is based on a fully ionic description of the material, with the shell model being used for the oxygen ions and a three-body potential representing the interactions of the niobium ions with the neighbouring oxygen ions. The potential set has been tested on the paraelectric phase, whose structure it reproduced to within a few per cent. The calculation of lattice properties including elastic constants and dielectric constants, as well as powder x-ray diffraction patterns of both phases, are reported.

Influence of thermal treatment on the Raman, infrared and TL responses of natural topaz

Abstract Analyses of thermoluminescence (TL) and thermally stimulated exoelectron emission have proved that the natural Brazilian topaz is a promising material for dosimetry of ionizing radiation. Topaz is an aluminum fluorosilicate with a general composition of Al 2 (SiO 4 )(F,OH) 2 whose main defect is the presence of OH − groups substituting for the F − ions. Analyses of topaz samples from Santo Antonio do Jacinto, MG, Brazil, showed that their TL responses are strongly affected by the temperature of pre-irradiation thermal treatment. This behavior was correlated to the changes observed in the infrared and Raman spectra and a model could be proposed for the charge trapping and recombination process in colourless topaz.

Computer modelling of : I. Interionic potentials and intrinsic defects

A computational study of is presented. Interionic potentials are fitted to experimental data and the resulting potentials used to calculate the defect behaviour. Energies of formation of basic defects are obtained and used to predict intrinsic disorder and to calculate activation energies for ion migration. This information is used to suggest the possible mechanisms involved in the ionic conductivity of the material.

Thermoluminescence mechanism of Mn2+, Mg2+ and Sr2+ doped calcite

Abstract In this work, the thermoluminescence properties of synthetic crystals of doped calcite were studied. Samples were doped with Mn 2+ , Mg 2+ or Sr 2+ , either individually or simultaneously with more than one of these impurities. TL glow curves, partial heating measurements, isometric curves, emission spectra and thermal treatment were performed, in order to investigate the role played by the impurities in the TL glow peaks of calcite. We conclude that the crystals doped with Mn 2+ show five TL peaks with emission spectra due only to the Mn 2+ . The relative intensity of these peaks is closely related to the other divalent dopant added in the solution (Sr 2+ or Mg 2+ ). These results suggest that although Sr 2+ and Mg 2+ act as TL activators stabilising slightly different electron traps, they are not directly connected to the Mn 2+ luminescence centre.