Optically Stimulated Luminescence Process Research Articles

Investigation on relation between TL and OSL of Li2B4O7:Cu, In

Polycrystal Li2B4O7 (LBO) doped with Cu and In was prepared and then sintered at different temperatures. X-ray diffraction (XRD) was applied to get the parameters of the LBO structure, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured, and a second-order exponential decay model was fitted to the OSL decay curves. The results indicate that the original number of OSL traps that have captured electroncs is linearly related with the sum of TL decay during the OSL process. Mean decay constant of OSL is related to the sintered temperature. The possible reason is that the sintered temperature affects the crystal sizes of the polycrystal, and consequently affects the stimulating lights’s intensity and the photoionization cross-section of the electrons, which have been captured by the traps.

Optically stimulated luminescence of magnesium aluminate [formula omitted] spinel

Magnesium aluminate spinel ( MgAl 2 O 4 ) is a crystal studied in detail mainly because of its radiation resistance and good optical and insulating features. A new characteristic of this material is presented here, which may be applied to radiation dosimetry. Spinel crystals present a high optically stimulated luminescence (OSL) signal linearly related to the absorbed dose of ionizing radiation. The correlation of OSL with thermoluminescence (TL) shown in the paper indicates that trapped carriers connected to at least three TL glow peaks (63, 260 and 540 ∘ C , 1 ∘ C s - 1 ) participate in the OSL process. Part of the OSL signal emitted by spinel fades very rapidly at room temperature but a more stable component of the emission can be properly separated and used as a dose indicator with good reproducibility.

Effect of high-dose irradiation on the optically stimulated luminescence of Al 2O 3:C

This paper examines the effect of high-dose irradiation on the optically stimulated luminescence (OSL) of Al 2O 3:C, principally on the shape of the OSL decay curve and on the OSL sensitivity. The effect of the degree of deep trap filling on the OSL was also studied by monitoring the sensitivity changes after doses of beta irradiation and after step-annealing of samples previously irradiated with high doses. The OSL response to dose shows a linear-supralinear-saturation behavior, with a decrease in the response for doses higher than those required for saturation. This behavior correlates with the sensitivity changes observed in the samples annealed only to 773 K , which show sensitization for doses up to 20– 50 Gy and desensitization for higher doses. Data from the step-annealing study leads to the suggestion that the sensitization is caused by the filling of deep electron traps, which become thermally unstable at 1100– 1200 K , whereas the desensitization is caused by the filling of deep hole traps, which become thermally unstable at 800– 875 K , along with a concomitant decrease in the concentration of recombination centers (F +-centers). Changes in the shape of the OSL decay curves are also observed at high doses, the decay becoming faster as the dose increases. These changes in the OSL decay curves are discussed in terms of multiple overlapping components, each characterized by different photoionization cross-sections. However, using numerical solutions of the rate equations for a simple model consisting of a main trap and a recombination center, it is shown that the kinetics of OSL process may also be partially responsible for the changes in the OSL curves at high doses in Al 2O 3:C. Finally, the implication of these results for the dosimetry of heavy charged particles is discussed.

Luminescence and OSL study of the inorganic compounds Tl+-doped (NH4)2BeF4 and (NH4)2SiF6

The search of materials with efficient optically stimulated luminescence (OSL) properties and a high hydrogen content for fast neutron dosimetry has led to the development of Tl+-doped ammonium salts (NH4)2SiF6 and (NH4)2BeF4. Preliminary OSL studies have shown that the OSL in (NH4)2SiF6:Tl+ and (NH4)2BeF4:Tl+is efficient. In order to optimise the OSL emission and its detection, the identification of the luminescent centres in the OSL process is necessary. This study focuses on the identification of the luminescent centres associated with Tl+ based on optical studies in the vacuum UV (VUV) at different temperatures.

Luminescence sensitivity changes in natural quartz induced by high temperature annealing: a high frequency EPR and OSL study

Quartz undergoes very significant luminescence sensitivity changes after high temperature annealing (0-1200 °C), with particular enhancement occurring between the phase transition temperatures 573 and 870 °C. In order to understand why this occurs, high frequency electron paramagnetic resonance (EPR), operating at 90 GHz, has been used to monitor the structure and population of defects in natural sedimentary quartz, following annealing and -irradiation. The results are compared with the optically stimulated luminescence (OSL) data of the same samples. It is shown that: (i) the structure and population of the dominant [AlO4]0 recombination centres are largely unaffected by the annealing process; (ii) the oxygen vacancy E´ centres are destroyed when annealed at temperatures between the phase transitions and; (iii) the numbers of both [TiO4/H+]0 and [TiO4/Li+]0 donors increase between 400 and 700 °C. Photo-EPR spectra are presented, providing evidence that both the Ti associated donors and Al acceptors are directly involved in the OSL process. The heat-induced changes in the population of these EPR defects is mirrored in part by the change in the luminescence sensitivity of several OSL components. Evidence is also presented suggesting that E´ may act as non-radiative centres competing in the OSL process.

Optically stimulated luminescence in KCl:Cu x-irradiated at room temperature

Optically stimulated luminescence (OSL) has been observed in single crystals of KCl:Cu x-irradiated at room temperature. It is shown that electrons are liberated from anion sites during the OSL process. The OSL predominantly involves emission due to radiative transition (d↔s) of monovalent copper ions present in the lattice. The OSL emission shows a strong temperature dependence indicating a thermally assisted process. Electron-hole recombination followed by energy transfer to the Cu activator is suggested as a possible OSL mechanism in KCl:Cu. Preliminary results of OSL in KBr:Cu are also presented.