D. Lapraz

Photoluminescence and thermoluminescence of titanium ions in sapphire crystals

Abstract Several titanium species (Ti 3+ , Ti 4+ , Ti 4+ -V Al clusters) were identified in sapphire samples from their optical spectra. In highly reduced samples, we observed only Ti 3+ centres while oxidized samples contain Ti 3+ and Ti 4+ ions as well. The formation of Ti 4+ ions occurs simultaneously with the formation of aluminium-vacancies which are charge compensators for Ti 4+ ions and act as hole traps in charge exchange process. We could observe locally and non-locally compensated Ti 4+ as well. It is shown that Ti 3+ is a deep hole trap while Ti 4+ is a deep electron trap. In the TL process they act as recombination centers for electrons and holes, respectively. However, in TL we observed only the emission of locally compensated Ti 4+ , probably because of spatial correlation.

Theoretical model for thermally stimulated luminescence, conductivity and exoelectronic emission

A theoretical model which takes into account thermally stimulated luminescence (TSL), conductivity (TSC) and exoelectronic emission (TSEE) is proposed in this article. The model is established for the case of a single type of electron trap, a single type of recombination centre and in the presence of thermally disconnected traps. It generalizes the model of Lewandowski and McKeever by taking the TSEE phenomenon into consideration. TSEE is described as resulting from the thermionic effect and so the model applies only to a thin solid film about 10 nm thick. As an application example, the influence of various parameters involved in the model on peak shape and position is investigated.

Thermally stimulated properties of CVD diamond films

Thermally stimulated luminescence ( TL), current (TSC ) and exoelectronic emission ( TSEE ) of diVerent CVD diamond films grown on silicon substrates have been studied in order to obtain information on defects created during the growth and which induce levels within the gap. TL and TSC have been performed between 100 and 600 K, whereas TSEE has been measured from 300 to 700 K. Several TL peaks located between 275 and 540 K are observed, with diVerent relative intensities depending on the samples. A single TL peak located at about 515‐540 K is associated with a trap level 0.8 eV deep. This level gives rise to TSC, whereas the peak located at 275 K, and which may be attributed to the presence of boron, does not give a TSC signal. A TSEE peak located at 595 K is measured for all the samples but cannot be correlated with TL and TSC peaks. This is probably due to the presence of defects that are present only near the surface of the films.

Influence of the irradiation temperature on TL sensitivity of Al2O3: C

Abstract Al 2 O 3 :C TL/OSL dosemeters were irradiated at different temperatures. TL sensitivity was found to decrease by about 40% with decreasing irradiation temperature between +30 and −100°C. High temperature TL peaks were shown to appear only if the irradiation temperature is higher than 200°C. Recombination of holes with electrons in the dosimetric traps was proposed as a mechanism to explain these phenomena.

Theoretical analysis of the simultaneous detection method of thermally stimulated conductivity (TSC) and luminescence (TSL); application to an alpha -Al2O3 monocrystal

A simultaneous detection analysis of thermostimulated luminescence (TSL) and electrical conductivity (TSC) is made using the approximate analytical models of first- and second-order kinetics. Some characteristics are developed and a new approach for evaluating the trapping depth is proposed and tested in the case of an alpha -alumina monocrystal.

Thermally stimulated exoelectronic emission of CVD diamond films

Exoemissive properties of several CVD diamond films (undoped or doped with nitrogen) are studied by the thermally stimulated exoelectronic emission (TSEE) method. Some experimental results are obtained after UV or X-ray irradiation. After UV irradiation, a single TSEE peak is observed at 605 or 625 K, depending upon the growth parameters. The existence of the exoemission signal is related to the surface morphology: facetted surfaces give rise to exoelectronic emission, more especially in the presence of both 111 and 100 faces, while smooth surfaces do not or only to a limit extent. A possible indication of negative electron affinity is observed at about 273 K.

L'instabilité des ions Eu3+ provoquée par le bombardement électronique dans les minéraux synthétiques observée par luminescence

Abstract Comparative study of luminescence properties of doped synthetic minerals (anhydrite, calcite, fluorite and zircon) by cathodoluminescence and fluorescence methods is presented. The Eu 3+ doped minerals (anhydrite; other sulfates; fluorite) exhibit partial reduction of Eu 3+ to Eu 2+ when they are studied by cathodoluminescence method. On the other hand, in the spectra of Eu 3+ doped calcite, strontianite and zircon, no redox reaction is observed.

Reply to Dr Käämbre's comment

In recent work we described a method which allowed the estimation of the effective electron affinity of α-alumina. The interpretation of these results has given rise to the comment from Dr Kaambre. Here, we develop some arguments in response to this comment.

Characterization of ceramics by thermoluminescence and exoelectronic emission

Abstract The various possibilities of thermoluminescence and thermostimulated exoelectronic emission in ceramic investigations are presented. Numerous examples are given.