Multiemitting Lanthanide-Organic Complexes with Abundant Uncoordinated Lewis Base Active Sites as Luminescence Probes for Temperature Sensing, Ion Detection, and White Light Emission Films

A series of isomorphic lanthanide-based metal organic complexes (LnMOCs), {[Ln(C₁₄H₁₀N₄O₄)_0.5(C₂O₄)_1.5(H₂O)₂]·3H₂O}_<i>n</i> (LnBTA, Ln = Eu, Tb, and Gd), and their doped complexes have been successfully synthesized using 2,5-di(1H-imidazol-1-yl)terephthalic acid (H₂BTA) as the organic ligand. The as-synthesized LnMOCs were characterized by single-crystal X-ray diffraction (XRD), powder XRD, and thermogravimetric analysis (TGA), and their stability was systematically evaluated under a wide pH range, long-term storage conditions, and various organic solvents. In the range of 303-403 K, the doped Cu@LnBTA (Ln = Eu and Tb) and Eu_0.15Tb_0.48Gd_0.37BTA show good temperature-dependent luminescence characteristics with maximum relative thermal sensitivities of 7.94% K^-1 (403 K for Eu_0.15Tb_0.48Gd_0.37BTA), 3.62% K^-1 (363 K for Cu@EuBTA), and 0.82% K^-1 (303 K for Cu@TbBTA). Luminescence temperature sensing studies indicated that EuBTA and TbBTA had significant luminescence quenching effects on Cu²⁺, Fe³⁺, and H⁺, which is mainly attributed to the interaction between the Lewis base sites in LnBTA (Ln = Eu and Tb) and the detected ions. It was noted that the <i>K</i>_<i>sv</i> value of TbBTA in detecting Cu²⁺ could reach 8.67 × 10³ M^-1 and the limit of detection (LOD) was 1.23 μM. In addition, the doped LnBTA, Eu_<i>x</i>Tb_<i>y</i>Gd_1<i>-x-y</i>BTA (<i>x</i> = 0.12, 0.12, 0.18, 0.21, 0.23, 0.24, 0.25; <i>y</i> = 0.48, 0.51, 0.43, 0.41, 0.41, 0.41, 0.41) were obtained by codoping with lanthanide ions. Especially, Eu_0.12Tb_0.48Gd_0.40BTA can achieve white light emission at an excitation wavelength of 325 nm, with CIE coordinates of (0.339, 0.334), a correlated color temperature of 5176 K, and a color rendering index (CRI) of 88. Meanwhile, the temperature response of the as-synthesized Eu_0.12Tb_0.48Gd_0.40BTA@PDMS film was also monitored, and its luminescent color reversibly changed from white at room temperature to orange at 353 K.