Collective Radiative Enhancement of Rare-Earth Ions in Lithium Niobate via Engineered Large-Area Nanohole Arrays

Conventional approaches to light-matter interactions rely on engineering photonic density of states. More recently, tailoring the spatial geometry of atoms or emitters themselves has emerged as a powerful and complementary route to control collective radiative properties. Here, we experimentally realize a geometry-engineered ensemble of rare-earth ions by fabricating a periodic array of subwavelength gold nanoholes on lithium niobate implanted with thulium ions, forming a semi-two-dimensional array of quantum emitters embedded in a high-index crystalline thin film. The hybrid structure can simultaneously support localized and lattice plasmon resonances from the metallic array and collective atomic resonances from the ion ensemble. Using time-resolved photoluminescence and temperature-dependent measurements, we observe enhanced radiative emission attributed to collective atomic effects mediated by the nanohole lattice, distinct from single-emitter Purcell enhancement. Our results demonstrate a new regime of light-matter interaction opening a pathway toward broadband and scalable, geometry-controlled quantum optical interfaces in solid-state platforms.