EPR Spectroscopy of the Mn2+ and Cu2+ Centres in Lithium and Potassium-Lithium Tetraborate Glasses

The electron paramagnetic resonance spectra of the glasses with Li2B4O7 and KLiB4O7 compositions doped with Mn and Cu were investigated. On the basis of obtained EPR spectra analysis it was shown that the Mn and Cu impurities are incorporated into the glass network as Mn2+ (S-6(5/2), 3d(5)) and Cu2+ (D-2(5/2), 3d(9)) ions. The Mn2+ EPR spectra in the glasses with Li2B4O7 and KLiB4O7 compositions are characterised by the following parameters, measured at T = 300 K: isotropic g-factor (g(iso) = 2.00 +/- 0.05), isotropic hyperfine constant (A(iso) - (8.65 +/- 0.05) mT) and peak-to-peak linewidth of hyperfine components Delta B-pp = (3.50 +/- 0.05) mT. The Cu2+ EPR spectra in the glasses with Li2B4O7 and KLiB4O7 compositions, registered at T = 300 K are characterised by the same g-values (g(parallel to) = 2.34 +/- 0.05, g(perpendicular to) = 2.06 +/- 0.05) and peak-to-peak line width of hyperfine components (Delta B-pp(parallel to) = (5.11 +/- 0.05) mT, Delta B-pp(perpendicular to) = (1.80 +/- 0.05) mT), whereas anisotropic hyperfine constants show some differences (A(parallel to) = (14.28 +/- 0.05) mT, A(perpendicular to) = (2.34 +/- 0.05) mT for glass with Li2B4O7 composition and A(parallel to) = (14.21 +/- 0.05) mT, A(perpendicular to) = (2.55 +/- 0.05) mT for glass with KLiB4O7 composition). The possible local structure of the Mn2+ and Cu2+ centres in the lithium and potassium-lithium tetraborate glass network has been considered.