EPR Spectroscopy of the Mn^{2+} and Cu^{2+} Centres in Lithium and Potassium-Lithium Tetraborate Glasses

The electron paramagnetic resonance spectra of the glasses with $Li_{2}B_{4}O_{7}$ and $KLiB_{4}O_{7}$ 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 $Mn^{2+} (\text{}^{6}S_{5//2}, 3d^{5})$ and $Cu^{2+} (\text{}^{2}D_{5//2}, 3d^{9})$ ions. The $Mn^{2+}$ EPR spectra in the glasses with $Li_{2}B_{4}O_{7}$ and $KLiB_{4}O_{7}$ compositions are characterised by the following parameters, measured at T = 300 K: isotropic g-factor ($g_\text{iso}$ = 2.00 ± 0.05), isotropic hyperfine constant ($A_\text{iso}$ = (8.65 ± 0.05) mT) and peak-to-peak linewidth of hyperfine components $ΔB_{pp}$ = (3.50 ± 0.05) mT. The $Cu^{2+}$ EPR spectra in the glasses with $Li_{2}B_{4}O_{7}$ and $KLiB_{4}O_{7}$ compositions, registered at T = 300 K are characterised by the same g-values ($g_∥$ = 2.34 ± 0.05, $g_⊥$ = 2.06 ± 0.05) and peak-to-peak line width of hyperfine components ($ΔB_{pp}^{∥}$ = (5.11 ± 0.05) mT, $ΔB_{pp}^{⊥}$ = (1.80 ± 0.05) mT), whereas anisotropic hyperfine constants show some differences ($A_{∥}$ = (14.28 ± 0.05) mT, $A_{⊥}$ = (2.34 ± 0.05) mT for glass with $Li_{2}B_{4}O_{7}$ composition and $A_{∥}$ = (14.21 ± 0.05) mT, $A_{⊥}$ = (2.55 ± 0.05) mT for glass with $KLiB_{4}O_{7}$ composition). The possible local structure of the $Mn^{2+}$ and $Cu^{2+}$ centres in the lithium and potassium-lithium tetraborate glass network has been considered.