Environmental influences of BaO on structure and ligand field parameters of Co2+inside K2O-AL2O3-CoO-BaO-B2O3 glass

The study of transition metal cations containing glass is a very important topic due to the need for new colored glass used in several optical applications. One of these transition metal cations is cobalt (Co) which have more than valence state (Co3+ and Co2+). Here, alumino-borate glass doped with constant cobalt oxide (CoO) content and different contents of barium oxide (BaO) were prepared by the melt-quenching technique. Structurally, the samples density increases, and the molar volume decreases with further additions of BaO. Also, FTIR spectra confirmed the presence of AlO4, AlO6, BO3, and BO4 structural units. Optically, it is confirmed that the absorption bands at about 574 nm and 1413 nm which are associated with 4A2(4F) -> 4T1(4P) and with 4A2(4F) -> 4T1(4F) optical transitions, respectively of Co2+ cations in tetrahedral coordination. These two optical transitions were used to study the ligand field parameters (10Dq and B). Also, these parameters were used to explain the environmental influences of BaO on the bonding nature between Co cations and their ligands. With increasing BaO content, the d-orbital shrinkage and high interaction between d-electrons of Co2+ ions result in a high tendency toward the ionicity of the bond nature between Co2+ ions and their ligands. Finally, we concluded the significant influence of BaO addition on the structure, electronic transitions and ligand field parameters of cobalt alumino-borate glasses.