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(C 14 H 10 N 4 O 4 ) 0.5 (C 2 O 4 ) 1.5 (H 2 O) 2 ]·3H 2 O} n (LnBTA, Ln = Eu, Tb, and Gd), and their doped complexes have been successfully synthesized using 2,5-di(1H-imidazol-1-yl)terephthalic acid (H 2 BTA) 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 0.15 Tb 0.48 Gd 0.37 BTA show good temperature-dependent luminescence characteristics with maximum relative thermal sensitivities of 7.94% K –1 (403 K for Eu 0.15 Tb 0.48 Gd 0.37 BTA), 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 Cu 2+, Fe 3+, 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 K sv value of TbBTA in detecting Cu 2+ could reach 8.67 × 10 3 M –1 and the limit of detection (LOD) was 1.23 μM. In addition, the doped LnBTA, Eu x Tb y Gd 1 –x–y BTA ( x = 0.12, 0.12, 0.18, 0.21, 0.23, 0.24, 0.25; y = 0.48, 0.51, 0.43, 0.41, 0.41, 0.41, 0.41) were obtained by codoping with lanthanide ions. Especially, Eu 0.12 Tb 0.48 Gd 0.40 BTA 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 0.12 Tb 0.48 Gd 0.40 BTA@PDMS film was also monitored, and its luminescent color reversibly changed from white at room temperature to orange at 353 K.