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.