EPR and optical absorption of Cr3+ in binary Na2O-B2O3 glasses

The optical absorption and EPR spectra of Cr³⁺ in binary sodium borate glasses have been studied as functions of chromium concentration and Na₂O/B₂O₃ ratio in the glass; the ligand field and EPR parameters have been calculated and were found to be independent of Cr₃₊ concentration in any particular glass. In low-alkali borate glasses (Na₂O = 11 or 14 mol %) a single symmetrical EPR line was observed with g_¦=g =1.984±0.001 corresponding to perfect octahedral symmetry of the Cr³⁺ ion in these glasses. With increasing Na₂O content of the glass, the EPR line becomes more asymmetric (characteristic two-peaked pattern); this has been explained as being due to axial elongation of the six co-ordinated Cr³⁺-complex in these glasses.