Niestierkina V. Influence of defects on radiative relaxation of BaF2, NaI and Y3Al5O12 based scintillators

This thesis is devoted to an integrated study of the influence of crystal structure defects on energy conversion processes in scintillators based on halide (BaF2 and NaI) and oxide (Y3Al5O12) dielectric compounds using absorption, luminescent and thermoluminescent techniques. The nature of scintillation efficiency losses in the studied crystals depends on the defects that are centers of trapping of charge carriers. Impurity centers and anion sublattice defects play the main role in doped BaF2-based crystals. Typical source of defects in Y3Al5O12 crystals is a stoichiometry deviation. The hygroscopicity and the resulting presence of oxygen impurities play the dominant role in the features of energy transfer and storage in NaI and NaI:Tl crystals. Models of intrinsic and impurity pre-radiation and radiation-induced defects are proposed. It was found that the introduction of Lu3+ ions in BaF2 scintillators allows suppressing the slow self-trapped excitons luminescence, while the efficiency of ultrafast core-valence transitions does not change. The possibility of obtaining high light yield for undoped Y3Al5O12 crystals is shown. It was found that Ca2+ ions can reduce the concentration of oxygen-containing impurities in NaI and NaI:Tl and improve the energy resolution of NaI:Tl,Ca crystals up to 6%. Keywords: BaF2, Y3Al5O12, NaI, intrinsic and impurity defects, scintillator, radiative recombination, luminescence center.