Crystalline environment of luminescent Tb³⁺ ions embedded in indium tin oxide thin films: A DFT and crystal field analysis assessment

We assess the local symmetry and crystal environment of trivalent terbium ions embedded in an indium tin oxide matrix with bixbyite structure. The Tb³⁺ ions tend to substitute In³⁺ ions in two different cationic sites (b and d). Density functional theory calculations suggest that the Tb³⁺ ions are mainly located at C₂ symmetry sites, relaxing selection rules and enabling electric dipole transitions, with the ⁵D₄→⁷F₂ transition being the most intense, providing a red color to the light emission. Photoluminescence emission spectrum under UV excitation at 83 K revealed 30 intra-4f transitions, which were assigned to the ⁷F_J ground multiplet of the Tb³⁺ ion. Crystal field analysis shows a strong alignment between calculated and observed energy levels, yielding a standard deviation of σ=15.1cm^-1. We believe these results can help to understand the activation mechanisms of Tb3+ luminescent centers in transparent conductive oxides, as well as the potential to modulate Tb³⁺ emission color through its crystalline environment.