On the formation of radiation-induced defects in fluoroaluminate glasses

The spectra of electron paramagnetic resonance (EPR) of fluoroaluminate glass (FAG-36) based on mineral usovite Ba2CaMgAlF14 were studied. The paramagnetic centers responsible for EPR signals were induced by ion bombardment of the substrates prepared from this glass. The N+, O+, Ar+ and Pb+ ions with energy E = 150 keV were used. The integrated dose D was 2 x 10(16) ions/cm(2). It is shown by means of isochronal anneal experiments and computer simulation of the EPR spectra that they contain four components: broad Gaussian line (GL) with g = 2.016 and sigma oscillating in the range 30-40; two anisotropic spectra with g(z) = 2.016, g(y) = 2.009; g(x) = 2.001 (FA(1)) and g(z) = 2.045; g(y) = 2.010; g(x) = 1.98 (FA(2)) as well as narrow isotropic line of Lorentzian shape with g = 2.0025 and Delta H = 0.6 mT. The comparison of obtained results with literature data for gamma-irradiated fluoride glasses and ion-implanted oxide glasses of different compositions permitted to conclude that GL is due to hole defects typical of fluoride glasses and localized on several anions (fluorines and oxygen(s)); anisotropic FA(1)- and FA(2)-spectra are attributed to molecular O-2(-)-ions, and narrow isotropic signal is supposedly assigned to big molecular ions (O2O-, O-4(-), CO+, CO-) located in voids of damaged implantation layer.