Mourad Benabdesselam

TL characterisation of a CVD diamond wafer for ionising radiation dosimetry

Abstract This work reports some thermoluminescent features of 28 samples cut from a free-standing polycrystalline diamond wafer grown by microwave assisted plasma CVD. All these samples show the same thermoluminescence (TL) peak at 540 K, particularly suitable for ionising radiation dosimetry. The homogeneity of synthesis in terms of TL responses as well as some criteria usually required for dosimetry work are studied.

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.

Thermoluminescence characterization of traps involved in the photodarkening of ytterbium-doped silica fibers

The photodarkening (PD) mechanisms of ytterbium-doped silica optical fibers have still not been elucidated, although hardening routes have been proposed. Most basic questions are still under debate about the assignment of the darkening excitation bands into the UV range, the nature of absorbing centers (photoionized centers or trapped carriers?), or of traps accepting photo-released carriers (electron or hole traps?). We used thermoluminescence measurements to characterize traps populated by different radiation types. It is notably demonstrated that photodarkening involves silica hole traps. The popular idea that color centers are formed upon carrier trapping is not consistent with our observations.

Thermally Stimulated Conductivity and Luminescence in Polycrystalline Diamond Films

Thermally stimulated currents (TSC) and thermoluminescence (TL) have been studied in polycrystalline diamond films of different qualities in order to gain information about the deep levels present within the bandgap of this material. The TL has been studied between 300 and 670 K after UV light illumination, and the TSC between 300 and 600 K after various excitations (UV light, from a tungsten ]amp, X-rays). TL and TSC peaks are observed at 470 and 560 K, and depend on the quality of the diamond and on the illumination conditions. At low temperature three TSC peaks appear at 245, 283 and 312 K after illumination with a tungsten lamp. A spectral analysis of the 470 K luminescence and electron emission measurement shows that the defect associated with this signal is an acceptor, and the hole released is trapped on a level 2.6 eV deep. Complementary ESR measurements show that paramagnetic nitrogen centers are not involved in the peak observed at 560 K.

Performance of Ge-Doped Optical Fiber as a Thermoluminescent Dosimeter

We have investigated the thermoluminescent response of three Germanium-doped silica-based optical fibers obtained by varying the drawing parameters from a unique preform. We compared under X-ray irradiation, their dosimetric properties to those of two widely used commercial dosimeters based on different technologies. Then, we investigated the potential of these optical fibers to monitor gamma rays at different doses and dose-rates, and to different fluences of particles (0.8 and 14 MeV neutrons and 63 MeV protons). Our results show that the thermoluminescence response of the Ge-doped optical fibers depends linearly on the direct ionizing dose (gamma-, X-rays) or on the indirect ionizing dose (protons, neutrons). As a consequence, this class of fibers is an excellent candidate for passive dosimetry in various fields from medical applications to high-energy physics.

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.

Thermoluminescence of nickel-doped synthetic diamond crystals

An investigation of the thermoluninescent response of nickel-doped synthetic diamond samples is reported. The glow curve obtained after x-ray irradiation or ultraviolet light illumination exhibits a main peak around 500 K, and three weaker ones around 380, 645, and 715 K. Among these peaks, two are attributed to nickel-related centers at 1.4±0.1 and 2.4±0.2 eV, respectively. Spectral analysis of the main thermoluminescence peak indicated a broad band around 2.3 eV, similar to the photoluminescence spectrum. Linearity of the response versus x-ray doses, thermal, and optical fading properties are reported. The results indicated that nickel-doped synthetic diamond overcomes most of the disadvantages of other synthetic diamond crystals for ionizing radiation dosimetry applications.

Thermoluminescence properties of nitrogen containing chemical vapour deposited diamond films

Abstract The behaviour of centres due to nitrogen impurities introduced during the growth process into the chemical vapour deposited (CVD) diamond lattice is reported for the first time by thermoluminescence (TL) studies between 300 and 670 K after 200–400 nm ultraviolet (deuterium lamp) illumination at 300 K (RT) in air. TL curves exhibit some glow peaks at 490, 520 and 620 K, characterized by activation energies of approximately 1.2, 1.4 and 1.9 eV, respectively. Spectral analysis of these peaks which reveals some differences due to nitrogen content in the films shows well defined emission bands and interesting features leading to a better knowledge of the broad red photoluminescence (PL) band observed in our films. Nitrogen addition during the growth of the CVD material leads to the quenching of both of the 1.68 eV line related to Si centre and the broad green band centred at 2.25 eV which were observed for the high quality film.

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.

Global View on Dose Rate Effects in Silica-Based Fibers and Devices Damaged by Radiation-Induced Carrier Trapping

We give a novel and very general treatment to a standard model describing dose rate effects in systems damaged by carrier trapping. This model is well adapted for optical fibers, but the lessons we draw may also be helpful to discuss dose rate effects (DRE) in electronic devices. By highlighting the few determinant ratios of physical parameters that govern the system behavior, we clarify when, how and how much dose rate effects affect trap filling and radiation-induced degradation. Critical dose rate, marking the demarcation between low and high dose rate regimes, is also estimated as a function of these parameters. Taking this step back is important to enlighten contradictory results reported on DRE behaviors. The dose and dose rate dependencies of trap filling measured on silica optical fibers, as well as the critical dose rate, are successfully reproduced with a single set of a few adjustable physical parameters.