Optical absorption and Raman studies of neutron-irradiated Gd 3 Ga 5 O 12 single crystals

Abstract In this work we have performed a comparative analysis of optical absorption and micro-Raman spectra for series of Gd 3 Ga 5 O 12 (GGG) single crystals irradiated by fast neutrons with fluences from 10 16  n/cm 2 to 10 18  n/cm 2 . It was found that the optical absorption spectra of non-irradiated Czochralski grown GGG consist of the relatively narrow lines in the UV spectral range related to the 4f– 4 f transitions in Gd 3+ . Transitions from the 6 S 7/2 ground state to the 6 P , 6 J and 6 D states in a Gd 3+ cation are clearly detected. For a GGG crystal containing Ca impurity ions, additional absorption band at 350 nm is observed, and it is tentatively ascribed to oxygen vacancies associated with Ca impurities. Several neutron-induced optical absorption bands, including ones related to F + centres, were observed in fast neutron-irradiated Gd 3 Ga 5 O 12 single crystals. Furthermore, clear evolution of the Raman spectra with neutron dose is also found. In particular, fine structure observed between 1350 and 1550 cm −1 is completely disappeared at high fluences, while several significant changes and the emergence of new transitions have been ascertained in spectral range of 100–850 cm −1 .