Erbium and praseodymium doped lithium tantalate electronic structure and metal-oxygen bonding analyses

Electronic information and optical properties coupled with the Quantum Theory of Atoms in Molecules (QTAIM) and Electron Localization Function (ELF) analyses are used to elucidate the erbium (Er⁺³) and praseodymium (Pr⁺³) intraband f–f transitions in the lithium tantalate (LiTaO₃) doped and co-doped configurations and the metal-oxygen bonding. The generalized gradient approximation calculations show that the Er⁺³- and Pr⁺³-4f bands appear closer to the conduction band bottom for Er⁺³ and Pr⁺³ at the Li sites and to the valance band top for Er⁺³ at the Ta sites. However, the corresponding hybrid functional calculations for the dopants at the Li site show that the Er⁺³ and Pr⁺³-4f bands spread in energy, which agrees with the observed intraband f–f transitions from the optical properties calculations. QTAIM shows that Ta-, Er⁺³-, and Pr⁺³-O bonding is incipient covalent for all configurations of this work. The absence of ELF in the metal-O regions aligns with QTAIM on the lack of strong covalent bonding in these compounds. This complementary insight highlights how weakly interacting metal-O atoms lead to delocalized electron density, a feature that influences the physical, electronic, and chemical behavior of the LiTaO₃.