On the crystalline environment of luminescent Tb$^{3+}$ ions embedded in indium tin oxide thin films: a DFT and Crystal field analysis assessment (2502.08517v1)
Abstract: We assess the local symmetry and crystal environment of trivalent terbium ions embedded in an indium tin oxide (ITO) matrix with bixbyite structure. The \mbox{Tb${3+}$} ions tend to substitute \mbox{In${3+}$} ions in two different cationic sites ($b$ and $d$). Density Functional Theory (DFT) calculations suggest that the \mbox{Tb${3+}$} ions are mainly located at $C_2$ symmetry sites relaxing selection rules and enabling electric dipole transitions, with the $5\text{D}_4\rightarrow\leftindex7{\text{F}}_2$ transition being the most intense, providing a red color to the light emission. Photoluminescence emission spectra under UV excitation at \qty{83}{\kelvin} revealed 30 intra-4$f$ transitions, which were assigned to the $\leftindex7{\text{F}}_J$ ground multiplet of the \mbox{Tb${3+}$} ion. Crystal-field analysis shows a strong alignment between calculated and observed energy levels, yielding a standard deviation of $\sigma=\qty{15.1}{\centi\per\metre}$. We believe these results can help to understand the activation mechanisms of \mbox{Tb${3+}$} luminescent centers in transparent conductive oxides, as well as the potential to modulate \mbox{Tb${3+}$} emission color through its crystalline environment.