Carbon dot/rare-earth compound composites: design principles, synthetic strategies, mechanisms, and applications

The integration of carbon dots (CDs) with rare-earth compounds (RE-compounds) has emerged as an important strategy for constructing multifunctional photofunctional systems capable of overcoming the intrinsic limitations of single-component luminescent materials. Owing to their broadband absorption, surface-/defect-state-mediated excited-state regulation, flexible interfacial chemistry, and favorable dispersibility, CDs can function not only as emissive centers but also as interfacial energy-regulation units. In contrast, structurally identifiable RE-compound phases or RE-doped host matrices provide narrow-band emission, long-lived excited states, upconversion/downconversion responses, and host-lattice-dependent photophysical property regulation. Through heterogeneous interfacial coupling and energy-level matching, CDs/RE-compounds can exhibit multilevel photophysical behaviors involving energy migration, excited-state redistribution, radiative/nonradiative transition modulation, and multichannel luminescence outputs that are inaccessible in isolated systems. Herein, recent advances in CDs/RE-compounds are systematically summarized from the perspective of structure-interface-excited-state-function relationships. Particular emphasis is placed on how heterogeneous interfaces govern photophysical processes through intrinsic structural regulation, matrix/interfacial stabilization, energy-transfer processes, and independent multimodal emission. Representative construction strategies, including one-step synthesis and multistep assembly, are discussed together with their influences on interfacial architectures and luminescence behaviors. Emerging applications in biomedicine, sensing, optoelectronics, information encryption, and energy-related fields are further highlighted. Finally, current challenges and future opportunities are discussed. This review aims to provide a deeper mechanistic understanding of interfacial photophysical regulation in CDs/RE-compounds and to guide their evolution from empirical hybrid materials toward predictable multifunctional photonic systems.