Lanthanide metal-organic frameworks (Ln-MOFs) have excellent optical properties and structural diversity, providing a unique platform for the development of fluorescent sensing and optical materials. In the work described herein, a series of isostructural 3D Ln-MOFs [Ln(L)(H₂O)]·2H₂O (Ln = Eu (1), Gd (2), Tb (3), H₃L = 3,3',3″-[1,3,5-benzenetriyltris(carbonylimino)]tris-benzoate) are fabricated under solvothermal conditions. The good thermal, water, and acid-base stabilities of 3 are prerequisites for fluorescent sensing applications. 3 can be used as a ratiometric broad-spectrum fluorescent sensor for toluenediamines (TDAs) in real urine with the advantages of visualization, ultrasensitivity, and selectivity. Interestingly, a smartphone-assisted intelligent sensing platform manifests promising results for the detection of TDAs, providing a chance for further development of portable diagnostic tools. In addition, by tuning the ratios of Eu³⁺/Tb³⁺ and Eu³⁺/Gd³⁺/Tb³⁺, nine bimetallic-doped Eu_xTb_1-x (x = 0.10-0.90, 4-12) and one trimetallic-doped Gd_0.95Tb_0.015Eu_0.035 (13) were obtained. 4-12 exhibit a gradient of luminescent colors from yellow-green to pink with different ratios of Eu³⁺ and Tb³⁺ ions. Meanwhile, the trimetallic-doped Gd_0.95Tb_0.015Eu_0.035 (13) shows near-white-light emission with a quantum yield of 8.76%. Interestingly, the inks made with 1-13 are invisible under ambient light but show visual color-tunable luminescence under a 254 nm UV lamp, which may facilitate their anti-counterfeiting applications.

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