Epitaxial CeO ₂ Films as a Host for Quantum Applications

In a highly purified host, the coherence of quantum emitters is ultimately limited by hyperfine interactions between the emitter and lattice nuclei possessing non‐zero nuclear magnetic moments. This limitation can only be mitigated through isotopic purification. In this work, we investigate CeO 2 as a host composed entirely of nuclei with zero nuclear moment. High‐quality CeO 2 thin films were grown by PLD and doped with Tm and Er ions. Structural characterization using X‐ray diffraction, atomic force microscopy, and ion channeling confirms single‐crystalline, atomically smooth films with dopants substitutionally incorporated at Ce lattice sites. Photoluminescence lifetime measurements show significantly longer lifetimes for Er‐doped CeO 2 (2.9 – 5.3 ms) compared with Tm‐doped films (14 – 68 µs). Moreover, the Er‐doped PLD films exhibit longer lifetimes at ∼1% dopant concentration than previously reported for MBE‐grown films. Density functional theory calculations reveal a substantial overlap between unoccupied O 2p and Tm 4f states near the valence band maximum, whereas Er 4f states remain well isolated. This electronic interaction likely introduces non‐radiative recombination pathways in Tm‐doped CeO 2 , explaining the reduced lifetimes. These findings highlight the importance of selecting appropriate dopant‐host combinations and optimized growth conditions to minimize non‐radiative channels for quantum applications.