M Jimenez de Castro

Thermoluminescent processes of MgAl2O4 irradiated at room temperature.

We are indebted to Dr. R. Heidinger (Kernforschungzentrum Karlsruhe, GFR) for the polycrystalline spinel sample supply, to Dr. E. R. Hodg son (CIEMAT, Madrid) for performing the TSC measurements, and to Dr. F. J. Lopez (Universidad Autonoma de Madrid, Spain) for his assistance in EPR measurements.

The effect of ZrO2 doping on mechanical and dielectric properties of Al2O3 and MgAl2O4

Abstract Different samples of zirconia-doped alumina and spinel ceramics have been obtained and characterized. Their mechanical and dielectric properties at high frequencies have been measured. The dependence of these properties on the concentrations of the different zirconia phases is discussed. From the results obtained it is concluded that the dispersion of tetragonal zirconia particles in the ceramics causes strength and toughness to be improved without almost any degradation in dielectric properties, while monoclinic zirconia increases the dielectric loss.

Thermoluminescence and thermostimulated currents in MgO X-irradiated at 80K

The thermoluminescence (TL) and the thermally stimulated currents (TSC) induced by X-irradiation in MgO single crystals at 80K have been studied. Glow peaks at 181 (I), 233 (II), 253 (III), 283 (IV), 354 (V) and 375 (VI) K as well as correlated TSC peaks have been observed. An emission band at 730 nm is common to all these glow peaks. In addition to this band, peaks I to IV exhibit a small emission band peaked at 340 nm and peak V emits a band peaked at 450 nm. The photoconductivity spectrum is similar to the corresponding light absorption spectrum at 80K in samples that have been irradiated at this temperature or heated up to 380K after irradiation at 80K. Measurements of photostimulated TL in samples previously X-irradiated at 80K and heated up to 380K have also been made. From these results it is concluded that the six glow peaks are due to hole traps. It has been found that previous treatments of the samples at and above room temperature, such as X- and electron irradiation, as well as quenching, have a similar effect on the low-temperature glow curve. From thermal annealing of this effect it is proposed that it is related to the aggregation state of the Fe3+-ion impurity, which acts as an electron trap in the irradiations at 80K.

Thermoluminescent processes in Al2O3 X-irradiated at 80 K

Abstract The thermoluminescence (TL) and the thermally stimulated currents (TSC) induced in Al 2 O 2 single crystals by X-irradiation at 80 K were studied. Glow peaks at 100 (I), 220 (II), 255 (III) and 275 (IV) K were observed. TSC peaks corresponding to glow peaks I, III and IV have also been obtained. No current peak at 220 (II) K was detected. Glow peaks I, III and IV exhibit common emission bands at 305, 420 and 705 mm, while a predominant band at 285 nm and a small one peaked at 705 nm appear in the emission spectrum of peak II. Optical absorption and photostimulated TL measurements were also made. From these results the ascription of TL processes to hole traps is discussed.

Thermoluminescent processes in NaCl irradiated at 80K

The thermoluminescence induced in NaCl by x-irradiation at 80K has been studied. To determine the nature of the mobile entities in the thermoluminescent processes observed below 300K, measurements have been made of the spectrum of thermally stimulated currents and the thermoluminescence induced by shining light in the F-centre absorption band on coloured samples have also been measured. Between 80 and 300K the thermoluminescence spectrum exhibits ten glow peaks. It has been found that five glow peaks are due to electron traps, one is due to a hole trap and the other four peaks have been ascribed to the recombination of thermally released interstitial halogen atoms with F centres. The activation energy and pre-exponential factors of these processes are given.

Thermoluminescence in MgAl2O4 X-ray irradiated at 90 K

Abstract Thermoluminescence (TL) peaks at 95, 105, 120, 130, 220 and 310 K, as well as their corresponding thermally stimulated current peaks (TSC), are induced by X-ray irradiation at 90 K in transparent polycrystalline MgAl 2 O 4 samples. All are due to electron release from traps. The last TL process seeems to be the same as the first one induced by irradiation at 290 K. Photon emissions from Cr 3+ , Mn 2+ and from electron-hole recombination at V centers have been observed. TL spectra at different wavelengths indicate that the emitting centers have different recombination probabilities at temperatures above 200 K. The role of a high concentration electron trap, which is a consequence of the antisite disorder of synthetic MgAl 2 O 4 , crystals, is discussed.

Stored energy in electron irradiated MgO

Abstract Measurements by differential thermal analysis, between room temperature and 1100°C, of the stored energy induced in MgO samples either by irradiation with 1.8 MeV electrons, or plastic deformation or thermal quenching, indicate that these treatments induce a similar type of damage. The energy released ranges between 102o and 1021 eV. g−1, which points to the formation of a large number of lattice defects which are aggregated in a variety of clusters or extended defects. Optical absorption measurements of the evolution of anion and cation vacancies after X-irradiation following isochronal annealing up to 1100°C support this proposal.

Effects of quenching on the thermoluminescence of MgO

Abstract The effect of quenching on the thermoluminescence (TL) of MgO above room temperature have been studied. Six glow peaks between 20 and 400°C appear in the TL spectrum. Quenching induces changes in the peak heights, but no effect on the emission spectra has been found to occur. The thermal annealing of these effects and their dependence on the quenching temperature have been obtained. From these results, the role of quenching induced vacancy defects in the TL processes is discussed.

On the nature of the thermally stimulated depolarization currents in MgO:Li

Abstract Two peaks at around 245 and 280 K are observed in the thermally stimulated depolarization (TSD) spectra of MgO:Li quenched in static air from temperatures above 1100 K. They are related to the ionization of [Li] 0 centers which are induced by this oxidizing quenching. The sample-thickness and applied-voltage dependences of the TSD results indicate, contrary to the previously proposed model based on Maxwell-Wagner polarization processes, that both peaks are due to the blocking character of the contracts at the sample-electrode interfaces.

Radiation-induced Schottky defects in NaCl

It has been found in nominally pure NaCl single-crystal samples that have been either gamma irradiated, plastically deformed or quenched into liquid nitrogen from 700 degrees C, that an additional quenching with a short residence time at the quenching temperature reveals the presence of dipolar defects by means of ionic thermocurrent (ITC) measurements. This procedure does not induce ITC signals in untreated samples. Since the occurrence of divacancies and divacancy clusters in plastically deformed or quenched samples is expected. It is pointed out that gamma irradiation may also form divacancies. The fact that all the ITC spectra of the samples treated in the above-indicated ways exhibit peaks at similar temperatures also supports this view. The parallelism observed between the stored energy spectra of these samples and the evolution of the ITC areas against the quenching temperature indicates that the two phenomena are related. The occurrence of dipolar defects is consistent with a previous proposal: that the stored energy release is due to the recombination of divacancies with alkali halide molecules.