Study of paramagnetic species in γ-irradiated fluoride glasses doped with transition metals

Electron paramagnetic resonance (EPR) and optical spectra were studied for fluoride glasses of two base compositions, fluorozirconate glass of 55ZrF(4)-15BaF(2)-6LaF(3)-4AlF(3)-20NaF (ZBLAN) type and fluoroaluminate glass (FAG) based on mineral usovite. The glasses were doped with fluorides or oxides of transition metals (TM) (V, Cr, Mn, Fe, Cu) in the amount from 0.03 to 0.6 wt%. The doped samples were gamma-irradiated at 77 or 300 K to doses from 10(6) to 1.6 x 10(8) rad. It was found that the formation of radiation induced defects (F-2(-), Zr3+, Y2+, O-2(-) and 'central resonance' defects) in these samples are suppressed by TM ions at concentrations of TM fluorides from 0.05 to 0.6 wt% depending on glass composition, the nature of defects, TM, dose of irradiation and the content of oxygen. The results are interpreted in terms of radiation induced redox reactions. It is shown that EPR lines of Cr3+ and Fe3+ ions near g = 2 for ZBLAN sample decrease in the intensity or disappear after gamma-irradiation of samples with 0.03 or 0.05 CrF3(Cr2O3) or FeF3(Fe2O3). This decrease is attributed to the conversion of Fe3+ ion to Fe2+ by electron trapping. It is shown that the shape of the g similar to 4.3 line for both fluoride glasses is distorted in comparison with that for unirradiated samples. It is assumed that the distortions are caused by the formation of radiation defects, including EPR-unobservable ones, near Fe3+ sites contributing to the g similar to 4.3 line. (C) 1999 Elsevier Science B.V. All rights reserved.