Multifunctional Lanthanide Metal–Organic Frameworks Act as Fluorescent Probes for the Detection of Cr2O72–, Fe3+, and TNP, White Light-Emitting Diodes, and Luminescence Thermometers

Two basically isostructural lanthanide-based metal–organic frameworks (Ln-MOFs), {[Eu(dptz)(H₂O)₂]Cl·3H₂O}_n (JLNU-10-Eu, JLNU = Jilin Normal University) and {[Tb(dptz)(NO₃)(H₂O)]·7H₂O}_n (JLNU-10-Tb), have been successfully synthesized by employing 3-(3,5-dicarboxylphenyl)-5-(pyrid-2-yl)-1H-1,2,4-triazole (H₂dptz) as a flexible carboxylic acid ligand through solvothermal reactions. Single-crystal structural studies on Ln-MOFs manifested that the compounds have a two-dimensional (2D) layered structure. Furthermore, fluorescence sensing experiments indicated that JLNU-10-Eu and JLNU-10-Tb had significant fluorescence quenching effects on Cr₂O₇^2–, Fe³⁺, and TNP. It should be noted that the K_SV value of JLNU-10-Eu in sensing Fe³⁺ could reach 7.36 × 10³, and the limit of detection (LOD) was 0.57. The luminescence quenching mechanism is discussed in detail through some relevant experiments. Additionally, a series of Ln-MOFs, JLNU-10-Eu_xTb_1–x (x = 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, and 0.1), have been obtained by simply regulating the molar ratio of Eu³⁺ and Tb³⁺. Particularly, JLNU-10-Eu_0.8Tb_0.2 can achieve white light emission at an excitation wavelength of 300 nm. The CIE coordinates are (0.316, 0.332), which are very approximate to ideal white light. JLNU-10-Eu_0.2Tb_0.8 as a luminescence thermometer exhibits good linearity over the temperature range of 303–373 K with a high sensitivity of 4.1% K^–1 at 373 K. The construction of multifunctional Ln-MOFs displays prospective applications in fluorescent probes, white light-emitting diodes, and luminescence thermometers.