Ion-Implanted Erbium in X-cut Thin-film Lithium Niobate: Luminescence and Low-Temperature Response

Abstract: This study presents a method for deterministic Er3+ doping of x-cut TFLN using focused ion beam (FIB) implantation with sub-100 nm spatial precision, enabling seamless integration of active rare-earth ions into this technologically relevant platform for lithium niobate integrated nanophotonics. Photoluminescence (PL) measurements from implanted regions reveal Stark-split 4f-4f transitions consistent with bulk Er-doped lithium niobate, indicating similar lattice occupation. Temperature-dependent PL measurements from 300 K to 5 K exhibit conventional behaviour down to approximately 50 K, followed by a marked decrease in the emission intensity and lifetime. This anomaly is attributed to a suppression of the pyroelectric response in LiNbO3 at low temperatures, which affects local electric fields and, consequently, Er3+ emission. The sensitivity of the PL response to the modulation frequency and polarization of the 980 nm excitation light is also consistent with possible mechanisms linking thermal effects and internal fields arising in the thin film. The results demonstrate a method for the targeted doping with Er3+ ions into the most widely used cut of TFLN for integrated photonic devices and provide further important considerations for their exploitation in cryogenic quantum devices.