Solvothermal synthesis and device fabrication of a Eu 3+ -based metal-organic framework as a turn-on and blue-shift fluorescence sensor toward Cr 3+ , Al 3+ and Ga 3 .

A novel three-dimensional Eu 3+ -based metal-organic framework with the formula {[(CH 3 ) 2 NH 2 ][Eu(BTDI)]·H 2 O·DMF} n (JXUST-25) was prepared by solvothermal method based on Eu 3+ and 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H 4 BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu 3+ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr 3+ , Al 3+ and Ga 3+ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr 3+ /Al 3+ /Ga 3+ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr 3+ /Al 3+ /Ga 3+ . It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr 3+ , Al 3+ and Ga 3+ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M 3+ ions may be caused by the host-guest interaction and the absorbance caused enhancement mechanism.