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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.