Thermoluminescence of zircon: a kinetic model

The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such amodel. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation. The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and comparedwith the EPR data associated with the rare-earth ions Tb3+ and Dy3+, which play a crucial role as hole traps and recombination centres. Inaddition, the behaviour of some of the SiOmn− centres has been compared with simulation results.

An EPR study of Er 3+ impurities in RbTiOPO 4 single crystals

An electron paramagnetic resonance (EPR) study of Er 3+ ions in single crystals of RbTiOPO 4 (RTP) is presented. The EPR spectra show the existence of six different Er 3+ centres. The g-matrix has been determined for these centres from the analysis of the angular dependences of the spectrum in three planes of the crystal. The study supports that erbium can enter the Rb + and Ti 4+ low-symmetry sites of RTP. This conclusion differs from those for KTP:Er 3+ and RTP codoped with Nb and Er. The different occupancies found for Er in these various crystals is suggested to be due to the differences in Er concentration. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200776.30.Kg Rare-earth ions and impurities, 42.70.Mp Nonlinear optical crystals,

Synchrotron-excited luminescence of natural zircon

The luminescence properties of two single zircon crystals from kimberlite of Yakutia have been studied, excited by the DORIS HASYLAB synchrotron, Germany, within energy range from the visible to the soft X-ray region (5-25, 50-200, and 500-620 eV) at temperatures of 300 and 10 K. The luminescence spectra in the range of 2.5 to 6.0 eV and excitation spectra of the main bands have been examined, the physical nature of the luminescence centers has been discussed, and the luminescence properties of a crystal containing growth (radiation) structural defects and a crystal with the same impurities but annealed in air at 1200°C are compared. The zoned structure of the mineral has been considered and the value of the energy gap (Eg) in the mineral has been estimated at 7.1 eV. Two groups of luminescence bands caused by impurities of intrinsic (growth, radiation) nature (Emax = 2.1, 2.7-2.8, and 3.2-3.3 eV) and matrix luminescence (Emax = 4.4-4.7 and 5.4 eV) probably with the participation of excitons were distinguished on the basis of selective excitation of zircon with different synchrotron energies relative to the gap value (Eexcit <Eg, Eexcit ~ Eg, and Eexcit > Eg). The short-lived component with a response time of 4 ns has been revealed in the afterglow of zircon in the region of 5.4 eV. © 2010 Pleiades Publishing, Ltd.ACKNOWLEDGMENTS This study was supported by the Presidium of the Russian Academy of Sciences (program 14 “Scientific Principles of Rational Nature Management”) and the Russian Foundation for Basic Research (project no. 09-05-00513)