J.F. de Lima

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.

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.

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.

An EXAFS study of the Ni dopant site in BaLiF

Extended x-ray absorption fine-structure measurements show that the dopant in predominantly substitutes on the site of the host lattice. Quantitative analysis of the results yields the details of the local environment of the ion.

Predicting the spectroscopic behaviour of Eu3+ in BaLiF3 via defect modelling and crystal field parameter calculations

Abstract The solution of Eu 3+ ions in BaLiF 3 is analysed through a defect simulation technique. The new relaxed positions of the nearest neighbour fluoride ions with respect to the central Eu 3+ ion are used to calculate the crystal field parameters. The set of non-zero crystal field components shows that the symmetry of the central ion is C 2h . The Eu 3+ ion dissolved in the matrix is thus generating a new site with a symmetry not usually found in the perovskite family. This explains the observed emission characteristics of the Eu 3+ ion that have been recently reported. It was found that the solution energy for Eu 3+ in the BaLiF 3 matrix is highly positive, indicating that the substitution of the Eu 3+ at the Ba 2+ site has a low probability, this latter result explaining why the observed emission intensities are weak.

Computer modelling of rare-earth dopants in BaLiF3

Doping of BaLiF3 by rare-earth ions is considered using computer modelling techniques. Solution energies for a range of possible doping mechanisms are calculated, and predictions made of doping sites and charge-compensation schemes. It is shown that there are definite trends going along the rare-earth series. Comparisons with experimental measurements are made where these are available.

Phototransferred thermoluminescence of quartz

Abstract We investigate the thermoluminescence (TL) of natural quartz at low temperatures. The samples were given different thermal treatments, followed by γ irradiation at room temperature, illumination with UV light at −100°C and readout of the TL signal. At least five peaks were observed in the TL glow curves of these samples. The dependence of these TL signals on the heating temperature and UV illumination enable us to propose plausible phototransfer mechanisms at low temperatures.

Computer modelling of : II. Defects produced by divalent dopants

A computational study of the doping of by divalent ions ( and ) is presented. The calculations provide information on the energies involved in the doping process, and the consequent lattice relaxation. Predictions of the sites occupied by the dopant ions are made, which are supported by experimental results.

Computer modelling of BaLiF3: III. Substitution of La3+, Nd3+ and Y3+ rare earth ions

Abstract A computational study of the doping of BaLiF3 by trivalent rare earth ions (La3+, Nd3+ and Y3+) is presented. The calculations provide information on the energies involved in the doping process, and the consequent lattice relaxation. La3+ and Nd3+ ions are predicted to substitute at the Ba2+ site, with charge compensation provided by Li+ vacancies, while Y3+ is predicted to substitute at the Li+ site, with Ba2+ vacancy compensation.