Influence of cobalt oxide on the structure,optical transitions and ligand field parameters of lithium phosphate glasses

The influences of cobalt oxide (CoO) additions on the structure, optical transitions, ligand field parameters and stability of lithium phosphate glasses have been investigated. A series of glass systems (LiPhCo-glasses) was successfully prepared through the melt quenching approach. The amorphous nature was confirmed from X-ray diffraction measurements. The density and molar volume followed the typical opposite behavior, where the latter showed a decreasing behavior with CoO additions. Furthermore, it was found that the LiPhCo-glasses gradually changed their color from colorless (Co-free sample) into bluish glasses with CoO additions, thereby evidencing the presence of Co²⁺ ions. This is consistent with the absorption band identified in the optical absorption spectra at ~562–572 nm, which is related to ⁴A₂(⁴F) →⁴T₁(⁴P) electronic transitions of Co²⁺ (3d⁷ electronic configuration) in tetrahedral symmetry. Additional absorption band is detected at ~1412–1448 nm, which is correlated to ⁴A₂(⁴F) →⁴T₁(⁴F) transitions of Co²⁺ ions in tetrahedral symmetry. These two absorption bands were employed to study the ligand field splitting ($10D{q}_{\mathrm{t}}$)and Racah parameter (B), which sheds the light into the bonding character between Co ions and its ligands. The analysis showed that $10D{q}_t$ (B) is increased (reduced) indicating more covalency and less stability within the glass matrix with Co additions.