Head of the Department: Prof. Paweł Bilski
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The luminescent properties of Al2O3 crystals obtained by Micro-Pulling-Down Method

Research project NCN PRELUDIUM 2014/13/N/ST8/01329

realized in years 2015-2017

Research team:
Dagmara Kulig (Wróbel) - project manager
Barbara Marczewska - research supervisor

Research project objective/ research hypothesis

      In the modern world we are still exposed to the effects of ionizing radiation from various sources: background radiation (space, rocks, soil or air) or artificial radiation. The radiation is applied in medicine, industry, agriculture, as well as in science and technology. In all these areas, it is necessary implementation and compliance with the principles of radiological protection, therefore, it is essential to assess the radiation exposure to people and to monitor environmental doses. Therefore, there is a great demand for the development and improvement of new techniques to measure doses, including the development of new types of detectors and ionising radiation dosimeters. A very interesting and not fully-known phosphor is Al2O3, which has the ability to detect ionizing radiation, i.e. it is capable of the accumulation of information on the absorbed dose of ionizing radiation, and after irradiation when stimulated with blue or green light it emits light, whose intensity is proportional to the cumulative dose. In comparison with other phosphors that require excitation using heating and leading gas during the measurement, and their readout will reset the information on the dose, the Al2O3 readout with the excitation of the blue LEDs is relatively simple, and the dose can be readout again even after a long time after the first readout. In spite of the routine use of alumina in individual and environmental dosimetry in some countries, such as, for example USA, it is so interesting and not a fully-known material that it is the subject of study of many research groups. The aim of this project is to investigate the thermoluminescent (TL) and optoluminescent (OSL) properties of Al2O3 crystals doped with various activators, such as C, Mg, Cu and Y. The crystals will be produced by Micro - Pulling - Down (MPD) method.

      The aim of project is also parameters optimization of the Al2O3 crystals growth process. The project will be focusing on the study of the phenomenon of luminescence of aluminum oxide produced in reducing atmosphere (Al2O3:C) and differently doped. The project will be researched in the Department of Radiation Physics and Dosimetry at the Institute of Nuclear Physics PAN, which has a unique position for manufacturing high-temperature oxide materials by MPD methods and is fully equipped with instruments for TL and OSL measurements. The Electron Paramagnetic Resonance (EPR) method will also be used in this project, for the purpose of investigations the Al2O3 powder or granules, deriving from different manufactures as starting material for the manufacture of the crystals.

Research project methodology

      From 2011, the Department of Radiation Physics and Dosimetry has a unique station for production of crystals by Micro-Pulling-Down (MPD) method. This method involves melting in the induction furnace batch material (in powder form) in a specially constructed crucible and pulling down the crystal through the hole in the bottom of the crucible. The first stage of the project will be the growth of Al2O3 crystals using this method. The investigation luminescent properties of alumina will be based on the well-known following methods: thermoluminescence (TL) and optically stimulated luminescence (OSL). The Department of Radiation Physics and Dosimetry is one of the leading centres dealing with issue and have the appropriate equipment to research the dosimetric properties of different materials. During the project, two readers will be used: Harshaw TLD Model 3500 Manual Reader for the thermoluminescence measurement in a wide range of temperatures (up to 600oC) at various heating rates and Risø TL/OSL reader Model DA-20, which is a multifunction machine allowing the reading TL and OSL. The measurements for irradiation of samples will use various sources of ionizing radiation, which are available in our Department: caesium source (137Cs) with energy 662 keV, the source of 60Co (1.25 MeV energy) from the therapeutic apparatus Theratron 760E and isotopic alpha (241Am) and beta (90Sr/90Y) radiation source. The first stage of this project will involve testing and comparison of batch material Al2O3 from various manufacturers using EPR method. These measurements will be performed in the University Centre for Innovation and Transfer of Technology and Natural Science Knowledge in Rzeszow on the Bruker multifrequency and multiresonance FT-EPR ELEXSYS E580 spectrometer.

Expected impact of the research project on the development of science, civilization and society

      The project will contribute to broaden the knowledge on the subject of luminescence phenomenon in Al2O3. Characteristics of thermally and optically stimulated luminescence properties of Al2O3 doped crystal allow greater understanding a nature of these phenomena in the research material. First of all, it will be possible to determine with which active centers we have to deal with. In addition the comparison of the glow curves of crystal Al2O3 doped with various activators allows us to assess the impact of the type and concentration of dopants on the nature of the glow curves. This knowledge will be important for the optimization of doping in order to achieve the best luminescent properties. A significant part of the work will constitute a PhD thesis the Head of project.