Core–Shell Lanthanide-Doped Nanoparticles@Eu-MOF Nanocomposites for Anticounterfeiting Applications

Heterogeneous nanocomposites constructed by lanthanide-doped nanoparticles and metal–organic frameworks (MOFs) have broad application prospects in therapy, catalysis, optical encoding, etc. However, the assembly of MOFs normally acquires delicate premodification of the surface of the nanoparticles. Herein, we demonstrate a simplified growth strategy of europium/1,3-benzenedicarboxylic acid (1,3-BDC) MOF on NaYF₄:Ce/Tb@NaYF₄ nanoparticles through a one-step reaction. Carboxylic acid groups are grafted on the surface of the nanoparticles via the ligand-exchange process between oleic acid and 1,3-BDC in the precursors of MOFs, which become growth sites for Eu-MOF under the reaction condition. An acid–base stimuli-responsive ligand N-(2-pyridinyl)­benzoylacetamide (HPBA) is coordinated with Eu³⁺ in the Eu-MOF, thereafter resulting in NaYF₄:Ce/Tb@NaYF₄@Eu-MOF@HPBA nanocomposites. The luminescence lifetime of Tb³⁺ could be controlled by the NaYF₄ inert layer. After exposure to NH₃/HAc vapor, the decay curve of Eu³⁺ centered at 615 nm has a corresponding change. Thus, the luminescence lifetime of Tb³⁺ and Eu³⁺ can be effectively tuned. This work sheds light on the synthesis of nanoparticle@MOF hybrid structures and time-resolved anticounterfeiting applications.