The Role of the Dopant in the Electronic Structure of Erbium-Doped \ch{TiO2} for Quantum Emit

Erbium-doped \ch{TiO2} materials are promising candidates for advancing quantum technologies, necessitating a thorough understanding of their electronic and crystal structures to tailor their properties and enhance coherence times. This study explored epitaxial erbium-doped rutile \ch{TiO2} films deposited on r-sapphire substrates using molecular beam epitaxy. Photoluminescence excitation spectroscopy demonstrated decreasing fluorescence lifetimes with erbium doping, indicating limited coherence times. Lattice distortions associated with \ch{Er^{3+}} were probed by X-ray absorption spectroscopy, indicating that erbium primarily occupies \ch{Ti^{4+}} sites and influences oxygen vacancies. Significant lattice distortions in the higher-order shells and full coordination around erbium suggest that additional defects are likely prevalent in these regions. These findings indicate that defects contribute to limited coherence times by introducing alternative decay pathways, leading to shorter fluorescence lifetimes.