Epr of Mn 2+ ions in Li 2O − Li 2F 2 − B 2O 3 glasses

Abstract

EPR spectra of Mn 2+ ions in Li 2O−Li 2F 2−B 2 O 3 glasses are investigated. Three resonances at g eff = 2.0, 3.0 and 4.3 are observed. No hyperfine structure due to 19F nuclei is observed. The overall spectral features are found to be independent of composition. The hyperfine coupling constant A is found to decrease with increasing content of LiF. The values of A are consistent with Mn 2+ in octahedral coordination. It was concluded that replacement of oxygen by fluorine may be responsible for the decrease in A values. There has been considerable interest in the physical properties of oxyhalo borate glasses in recent years because of their fast ionic conductivity [1–4]. Mn 2+ is known to be a good inorganic probe for structural studies and can be easily dissolved in the Li 2 O−Li 2F 2−B 2 O 3 glass system. We consider it interesting to investigate the EPR spectra of the Mn 2+ ion in this glass system, because it is known in the literature [7] that specific symmetry features may often be associated with various EPR resonances of the Mn 2 ion. A thorough discussion of the EPR spectra of lithium borate glasses doped with Mn 2+ was given by Griscom and Griscom [13] who interepreted the spectra on the basis of a spin Hamiltonian neglecting all fourth order terms. In this communication, we report the EPR spectra of Mn 2+ in (30−X) Li 2O−X Li 2 F 2 − 70 B 2O 3 glasses (hereafter called LFB), in continuation of our earlier studies on these glasses [5,6]. LFB glasses with 1 mol % Mn 2+ were prepared for the investigation and the composition of the glasses under study is presented in Table I. Lithium carbonate, boric acid and lithium fluoride were mixed to form a batch of 10 g. Each batch was first sintered at about 823K and then melted in porcelain crucibles in an electric furnace at a temperature of 1323K. The melts were quenched by pouring them onto a polished stainless steel plate and quickly pressed by another stainless steel block. The lithium fluoride content was varied from X = 0 to X = 10 only, as higher concentrations experience a serious evaporization loss of halogen [1].