Interfacial chemical compatibility-driven coumarin sensitization of two-dimensional rare-earth oxide nanoplatelets

Rare-earth oxide (REO) nanomaterials are promising photonic platforms, yet their practical emission efficiency is limited by the intrinsically weak absorption of parity-forbidden 4f-4f transitions. Here, we report a coumarin-based molecular sensitization strategy that markedly enhances the photoluminescence of Eu-doped Y₂O₃ nanoplatelets by addressing ligand-oxide interfacial chemistry. Using four coumarin derivatives with identical chromophore backbones but varied anchoring-group acidities, we reveal that interfacial chemical compatibility, rather than energy-level alignment alone, governs sensitization efficiency. Strongly acidic carboxylic acid groups induce surface reconstruction and defect formation, leading to pronounced nonradiative quenching, whereas ester and phenolic hydroxyl functionalities enable stable surface anchoring while preserving oxide lattice integrity. The optimal ligand, ethyl 7-hydroxycoumarin-3-carboxylate (EHC), delivers a 149-fold increase in Eu³⁺ emission by suppressing defect-mediated nonradiative pathways without compromising the structural integrity of the oxide lattice. Furthermore, the coexistence of fast, broadband ligand S1 emission and slow, narrowband Eu³⁺ emission within a single hybrid nanomaterial enables a proof-of-concept demonstration of dual-channel optical signal routing and information encryption. Our work establishes that beyond conventional energy-level matching, interfacial chemical compatibility serves as a crucial design principle for molecularly sensitized REO nanomaterials, providing guidance for the development of robust, efficient, and multifunctional rare-earth nanophotonic emitters.