Effect of structural changes on luminescent and dosimetric properties of nanoscale aluminum oxide.

Variations of the particle size and porosity of the alumina ceramics synthesized by annealing compacted nanopowder at 1500-1700°Ð¡ in vacuum for various periods of time have been studied by SEM. Particle size distributions, which depend on the conditions of the ceramics synthesis, were obtained and discussed. The formation of fine grains and the growth of their fraction with the increasing annealing temperature increase the thermoluminescence intensity and expands the usable dose range upwards.

Dosimetric response for crystalline and nanostructured aluminium oxide to a high-current pulse electron beam.

The main thermoluminescent (TL) and dosimetric properties of the detectors based on anion-defective crystalline and nanostructured aluminium oxide after exposure to a high-current pulse electron beam are studied. TL peaks associated with deep-trapping centres are registered. It is shown that the use of deep-trap TL at 200-600°Ð¡ allows registering absorbed doses up to 750 kGy for single-crystalline detectors and those up to 6 kGy for nanostructured ones. A wide range of the doses registered, high reproducibility of the TL signal and low fading contribute to a possibility of using single-crystalline and nanostructured aluminium oxide for the dosimetry of high-current pulse electron beams.

Mechanism of quantum dot luminescence excitation within implanted SiO2:Si:C films.

Results of the investigation of photoluminescence (PL) mechanisms for silicon dioxide films implanted with ions of silicon (100 keV; 7 × 10(16) cm(-2)) and carbon (50 keV; 7 × 10(15)-1.5 × 10(17) cm(-2)) are presented. The spectral, kinetic and thermal activation properties of the quantum dots (Si, C and SiC) formed by a subsequent annealing were studied by means of time-resolved luminescence spectroscopy under selective synchrotron radiation excitation. Independent quantum dot PL excitation channels involving energy transfer from the SiO(2) matrix point defects and excitons were discovered. A resonant mechanism of the energy transfer from the matrix point defects (E' and ODC) is shown to provide the fastest PL decay of nanosecond order. The critical distances (6-9 nm) of energy transport between the bulk defects and nanoclusters were determined in terms of the Inokuti-Hirayama model. An exchange interaction mechanism is realized between the surface defects (E(s)'-centres) and the luminescent nanoparticles. The peculiarities of an anomalous PL temperature dependence are explained in terms of a nonradiative energy transfer from the matrix excitons. It is established that resonant transfer to the luminescence centre triplet state is realized in the case of self-trapped excitons. In contrast, the PL excitation via free excitons includes the stages of energy transfer to the singlet state, thermally activated singlet-triplet conversion and radiative recombination.

Deep-trap competition model for TL in alpha-Al2O3:C heating stage.

The present report deals with the experimental observations of the thermally stimulated migration of charge carriers from trapping centres responsible for the main thermoluminescence (TL) peak at 450 K to a deep trap and, also, the optically stimulated transport of carriers from the deep trap to the main trap, which gives rise to the phototransferred TL at 450 K, in anion-defective alpha-Al2O3 crystals. The obtained results provide an experimental proof to the adequacy of the assumptions made in the model of the mutual interaction of the main and deep traps in the crystals under study.

Thermoluminescent dosemeters based on TLD-500 detectors for control of neutron fields.

The results of a study dealing with detection of neutrons in thermoluminescent (TL) photon radiation detectors, type TLD-500, based on an anion-defective corundum have been reported. The detection method uses the transformation of neutron radiation into gamma radiation arising when neutrons are captured by cadmium nuclei. A comparative analysis of the data obtained with the TL detectors and results of radiometric measurements suggested applicability of this method. A sensor with an optimal embodiment providing a relatively high sensitivity has been developed.

Thermoluminescent and dosimetric properties of anion-defective alpha-Al2O3 single crystals with filled deep traps.

Some new experimental results illustrating the effect of deep traps on luminescent and dosimetric properties of anion-defective single crystals of alpha-Al2O3 have been described. It was found that deep traps had an electronic origin. They were filled thanks to the photoionisation of F-centres and their filling was accompanied by the conversion of F-->F+ centres. The experiments revealed an interactive interaction of deep trapping centres. A model taking into account the thermal ionisation of excited states of F-centres was proposed. This model describes the trap filling process and mechanisms of the radio-, photo- and thermoluminescence, TSC and TSEE of the crystals under study. The sensitivity of TLD-500 detectors based on anion-defective alpha-Al2O3 equalised when deep trapping centres were filled.

The effect of thermally stimulated photoconversion of oxygen centres on the sensitivity of TLD-500 dosimetric crystals.

The influence of UV radiation at a high temperature on the luminescent properties of oxygen-deficient corundum was studied. Efficient photoconversion, F- => F+-centres, which leads to appearance of the 3.76 eV F+-centre emission in the main dosimetric TL peak and the 5.91 eV band in luminescence excitation spectra of this centre, was found. Correlation between the integral intensity of the TL peak in the 3.76 eV emission band and the intensity of the 5.91 eV excitation band was established. Probable mechanisms of the thermostimulated photoconversion and TL in the F+-centre emission band are discussed.

Transformation of the excitation energy in aniondefective corundum.

Some regular features of the excitation energy transformation in anion-defective crystals of alpha-Al2O3 were analysed by the sub-nanosecond spectroscopic method. The samples were excited using synchrotron radiation and high-density pulsed electron beams. It was shown that much of the energy of the ionising radiation absorbed by the crystals was liberated as the luminescence of F- and F-centres immediately at the moment of irradiation. Luminescence of F+-centres dominated in the nanosecond range, while luminescence of F-centres prevailed in the millisecond range. The excitation energy transformation processes and their kinetics were governed by the temperature, the concentration ratio of intrinsic defects in alpha-Al2O3 crystals, and the excitation density.