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

Abstract

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 (10Dqt)and Racah parameter (B), which sheds the light into the bonding character between Co ions and its ligands. The analysis showed that 10Dqt (B) is increased (reduced) indicating more covalency and less stability within the glass matrix with Co additions.