Time-Resolved Spectroscopy of Neutron Irradiated GSO:Ce and YSO:Ce Crystals

Cerium-doped yttrium and gadolinium oxyorthosilicates (Y2SiO5:Ce and Gd2SiO5:Ce) has been known to be very good scintillators with high light output and small decay time, and excellent radiation and chemical hardness. These crystals are widely used in many applications of radiation detectors and, therefore, are required to have a high radiation resistance. The radiation damage of gadolinium oxyorthosilicate was first studied by Massaki Kobayashi [1]. For the first time the existence of defects in polycrystalline yttrium oxyorthosilicate was discussed in 2004 by Aitasalo et al [2] and the weak luminescence bands peaked at 484 and 587 nm probable connected with anion vacancies (Fand F+-centers) were observed. However, until recent time there is no reported data on the detailed analysis of radiation defects in these compounds. Therefore, the problem of these compounds radiation modification is remained open. In the present work the formation of radiationstimulated defects under neutron irradiation in oxyorthosilicate crystals Y2SiO5:Ce (0.1 mol.%) and Gd2SiO5:Ce (0.5 mol.%) grown by Czochralski method was investigated. The samples were irradiated by fast neutrons with fluence of 4·10 cm in the hot camera of research reactor IVV-2M (Zarechny, Russia). After that the isochronous annealing up to 700 C was carried out. The primary measurements of absorption, photoluminescence (PL), PL excitation, X-Rayluminescence, thermostimulated luminescence spectra at every annealing step were carried out at the Experimental Physics Department of Ural State Technical University (Yekaterinburg, Russia). Time-resolved PL measurements before and after neutron irradiation of samples and after the annealing up to 700 C were carried out at the SUPERLUMI station at HASYLAB (DESY). The significant growth of sample’s optical density taking place at energies E > 3.5 eV (UV-region) indicate on the defect formation of crystal lattice. In the PL and X-Ray-luminescence spectra the new bands at energy of 2.0-2.5 eV were found out and they could be connected with producing defects (the luminescence centers). The decay kinetics of these bands and the thermostimulated luminescence curves have shown in the irradiated crystals the appearance of new centers – the luminescence centers and the trapping centers. Therefore, in this work we have first observed that the fast neutron irradiation with fluence of 4·10 cm leads to the effective generation of defects. The nature of these defects is discussed.