ESR and optical absorption of Cu 2+ in Na 2OSiO 2 glasses

Abstract

ESR and optical absorption spectra of Cu 2+ in xNa 2O(100− x)SiO 2 glasses were measured, where x ranges from 12 to 70 mol% Na 2O. This glass system was divided into three composition regions, 12 ≲ x ≲ 37, 37 ≲ x ≲ 55 and 55 ≲ x, from the composition dependence of the ligand field transition energy and spin hamiltonian parameters of Cu 2+. Two boundary compositions (37 and 55 mol%) between the two adjacent regions agreed with the eutectics in the equilibrium phase diagram. Two types of Cu 2+-complexes, with less basic ligands (HFS-1) and much more basic ones (HFS-2), were detected in ESR for ultra-high soda glasses ( x ≳ 55). The distribution of the ESR parameters due to the fluctuation of ligand fields was negligible for HFS-2 compared with that for other glasses. The Cu 2+ ion responsible for HFS-2 was considered to distribute in the microphase of orthosilicate. Imagawa's basicity, the covalency of the bondings between Cu 2+ and ligands, was calculated by using Maki and McGarvey's analysis. The basicity of σ-type symmetry remained constant, irrespective of the glass composition, and the value was identical with those for other oxyanionic glasses. The π-type basicity was also constant for the glasses of x ≲ 55. Two different basicities, each corresponding to HFS-1 or 2, were obtained for the glasses of x ≳ 55. The value derived from HFS-1 was identical with those for x < 55 glasses, whereas that derived from HFS-2 suggested the formation of much more basic ligands.