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.