Tunable high-efficiency Eu/Tb-MOFs enabling ultrasensitive ion detection and advanced anti-counterfeiting

A series of europium/terbium bimetallic metal–organic frameworks (Eu x Tb 1-x -MOFs) with tunable luminescence and high photoluminescence quantum yield (PLQY) were synthesized via a one-step hydrothermal method using 2,2′-biphenyldicarboxylic acid and 1,10-phenanthroline as mixed ligands. By precisely adjusting the Eu 3+ /Tb 3+ ratio, a continuously tunable emission color from red to green was achieved. The optimized material, Eu 0.04 Tb 0.96 -MOF, exhibited a superior PLQY of 52.17% along with excellent thermal, aqueous, pH and photostability. This material served as a dual-functional platform. As a high-performance fluorescent sensor, Eu 0.04 Tb 0.96 -MOF enabled the multiplexed and ultrasensitive detection of three priority water pollutants: Hg 2+ , CrO 4 2− and Cr 2 O 7 2− . It achieved high sensitivity (Ksᴠ: 7.609 × 10 4  M −1 for Hg 2+ , 4.369 × 10 4  M −1 for CrO 4 2− and 1.894 × 10 5  M −1 for Cr 2 O 7 2− ) and nanomolar-level detection limits (8.55 nM, 50 nM and 6.95 nM, respectively). The sensor also demonstrated outstanding selectivity, anti-interference capability, reusability and practical feasibility. Mechanistic investigations revealed that the quenching by CrO 4 2− /Cr 2 O 7 2− proceeded via competitive absorption, while Hg 2+ detection involved intramolecular photoinduced electron transfer (PET) within preformed complex. Furthermore, leveraging the precisely tunable emission of Eu x Tb 1-x -MOFs, advanced anti-counterfeiting and information encryption applications were demonstrated, including (1) a high-security QR code system based on spectral encoding for rapid mobile verification, (2) multicolor fluorescent inks for patterns hidden under daylight but visible under UV illumination, and (3) high-contrast visualization of latent fingerprints with clear ridge details. This study presents the rational design of tunable high-efficiency Ln-MOFs, establishing a versatile dual-functional platform that bridges high-performance environmental sensing and advanced optical security applications.