Spectroscopic investigations and physical properties of Mn doped mixed alkali zinc borate glasses

Spectroscopic investigations on Mn²⁺ doped 20ZnO + xLi₂O + (30−x)Na₂O + 50B₂O₃ (5 ≤ x ≤ 25) (ZLNB) glasses reveal the non-linear behavior in their physical and structural properties. FT-IR spectra of ZLNB glasses reveal diborate units in the borate network. EPR spectra exhibit characteristic resonance signals of Mn²⁺ ions. A well resolved six line hyperfine structure around g = 2.02 corresponds to the sites of Type II, and a weak broad shoulder around g = 2.7 followed by an unresolved intense signal at g = 4.25 corresponding to sites of Type I are observed for their respective transitions. A large value of zero-field splitting parameter (D) is observed and it behaves non-linearly, reaches a maximum at x = 15 mol% with increase in Li₂O content. Δg values reveal the ionic nature of glass systems. Optical absorption spectra suggest the distorted octahedral site symmetry of Mn²⁺ ions in the host. Mixed alkali effect is evident in bandgap and Urbach energies.