Recombination luminescence of doped borates: origin and application prospects in dosimetry
Date
2017-05-26
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Abstract
Viimase 30-aasta jooksul on märkimisvääne hulk teadus- ja arendustegevust keskendunud boraatidel põhinevate materjalide uurimisele. Liitiumtetraboraat on leidnud kasutust erinevates tehnilistes valdkondades tema sobilike füüsikaliste omaduste tõttu. Tulenevalt liitiumtetraboraadi laiadest füüsikaliste omaduste hulgast on need leidnud kasutust erinevates tehnilistes valdkondades. Tulenevalt oma pieso-elektrilistest omadustest kasutakse liitumtetraboraadi monokristalle pindakustiliste lainete filtritena televiisorites ja teistes signaalitöötlus-seadmetes. Kõige olulisema omadusena tuleb esile tuua liitiumtetraboraadi tiheduse sarnasust pehmele inimkoele, millest johtuvalt peetakse seda materjali koe-ekvivalentseks termoluminestsents-materjaliks, mis on äratanud tähelepanu dosimeetria rakendustes. Nimelt on oluline märkida, et pole palju materjale, mis oleksid samaaegselt nii koe-ekvivalentsed ja ka sobilikud materjalid kasutamiseks kliinilistes dosimeetrilistes rakendustes. Liitiumtetraboraadi lisandamisel erinevate haruldaste muldmetalli või siirdemetalli ioonidega on täheldatud selle materjali tundlikkuse kasvu ioniseeriva kiirguse suhtes, mis teatavatel juhtudel ületab isegi laialt levinud LiF:Mg,Ti (TLD-100) dosimeetermaterjali tundlikkust. Olenemata sellest, et läbi on viidud hulgaliselt uurimusi erinevalt lisandatud monokristallide ja keraamiliste materjalide termostimuleeritud luminestsentsi uurimiseks, on saadud tulemused rekombinatisooni mehanismide seisukohast senini vastuolulised.
Käesoleva töö raames uuriti koe-ekvivalentse dosimeetria rakenduste jaoks sobivaid lisandamata liitium tetraboraadi (Li2B4O7, või LTB) ja Cu+, Ag+, Mn2+ ja Be2+ ioonidega lisandatud kristalle ja keraamilisi materjale erinevate luminestsents-spektroskoopia meetodite abil. Peamiseks eesmärgiks oli kindlaks määrata dosimeetrilisteks rakendusteks tähtsad laengukandja-rekombinatsiooni mehhanismid, samuti energia ülekande, salvestuse ja rekombinatsiooni mehhanismid. Spektroskoopiliste metoodikate kõrvutamisel elektroni paramagnetilise resonantsi tulemuste ja teoreetiliste arvutustega leiti, et saadud tulemused lisavad olulist infot uute dosimeeter materjalide väljatöötamiseks.
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 tissue-equivalent 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
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 tissue-equivalent 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
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
boraadid, rekombinatsioon, optilised omadused, borates, recombination reaction, optical properties