Towards superior structural, optical and magnetic properties, and ligand field effects of B2O3–ZnO–CoO glass doped with alkaline metal earth cations.

Herein, the effect of changing the alkaline earth metal cations type on the structure-properties of cobalt zinc borate glass was demonstrated. A series of spectroscopic analyses such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), optical absorption, electron spin resonance (ESR) spectra, and mass density were carried out to scrutinize these effects. The glass structure was confirmed using XRD. The mass density and molar volume increased in the order of Ca < Sr < Ba, increasing the densification and connectivity of glass network. FT-IR analysis exhibited that the increased number of B O 4 units and decreased number of nonbridging oxygen (NBO) are attributed to the decrease in cation field strength in the order of Ca > Sr > Ba. Optical absorption spectra showed a single optical transition of Co 2 + cations in octahedral sites at ⁓ 502 nm, which is owing to 4 T 1 g (F) → 2 T 1 g H , and two transitions at ⁓ 572 nm and 1577 nm, which are owing to 4 A 2 (4 F) → 4 T 1 4 P and 4 A 2 (4 F) → 4 T 1 g 4 F of Co 2 + cations in tetrahedral sites, respectively. These optical transitions were exploited to evaluate the effect of changing the type of alkaline earth cations using ligand field theory. The crystal field strength (Dq) and inter-electronic repulsion (B and C) suggest that the ionic environment around the cobalt cations increases from Ca to Ba. Finally, ESR spectra indicated that cobalt ions exist in divalent states with more domination of tetrahedral sites than octahedral ones, in good accordance with the increase in mass density, the conversion to tetrahedrally-coordinated boron atoms ( BO 4 ), the decrease in NBOs, and the increase in optical band gap energy. The obtained values of covalency parameter ( K 0 ) increased from 0.833 for Ca, 0.878 for Sr, and 0.893 for Ba confirm the ionic nature. These obtained findings render these glasses a decent contender as optical material in the optics realm. [ABSTRACT FROM AUTHOR]