Ivo Romet will defend his doctoral theses titeled "Recombination luminescence of doped borates: origin and application prospects in dosimetry" on 27. June 2017 at 14.15 at W. Ostwaldi 1, room B103.
Dr Vitali Nagirnõi, Institute of Physics, University of Tartu
Dr Anatoli Popov Latvian University
During the recent 30 years, a considerable amount of research and development has been focused on borate based materials mainly because of their high potential in a large variety of technical applications. Due to its piezoelectric properties lithium tetraborate single crystals has been used as a substrate material for surface acoustic wave devices in TV and signal processing techniques. Most importantly lithium tetraborate effectively matches human tissue and for that reason it has been considered as a tissueequivalent thermostimulated luminescence material attractive for radiology diagnostics. It is important to note that there are only very few tissue equivalent materials suitable for dosimetry, particularly in clinical applications. When doped with various rare-earth or transition metal ions it has been shown an elevated sensitivity to ionizing radiation, exceeding that of well-known LiF:Mg,Ti (TLD-100). Although there are a numbers of studies devoted for investigating thermostimulated luminescence in variously doped complex ceramic samples and single crystals, the results on recombination mechanism are up to date controversial. In present work undoped lithium tetraborate (Li2B4O7, or LTB) as well as LTB crystals and ceramics doped with Cu+ , Ag+ , Mn2+ , and Be2+ ions, suitable for tissue equivalent dosimetry were investigated by the means of various luminescence spectroscopy techniques as the main investigation methods. The main purpose of the study was to determine the recombination mechanisms of energy transfer, charge carrier storage and recombination relevant for dosimetric application of the materials studied. Obtained results were approved by the electron paramagnetic resonance measurements and theoretical calculations, offering altogether an important insight in favour of developing a new type of dosimetric material with high sensitivity to ionizing radiation.