Ultrasound-assisted synthesis of luminescent micro-and nanocrystalline eu-based mofs as luminescent probes for heavy metal ions

The luminescent coarse-, micro-and nanocrystalline europium(III) terephthalate tetrahy-drate (Eu2bdc3‧4H2O) metal-organic frameworks were synthesized by the ultrasound-assisted wet-chemical method. Electron micrographs show that the europium(III) terephthalate microparticles are 7 μm long leaf-like plates. According to the dynamic light scattering technique, the average size of the Eu2bdc3‧4H2O nanoparticles is equal to about 8 ± 2 nm. Thereby, the reported Eu2bdc3‧4H2O nanoparticles are the smallest nanosized rare-earth-based MOF crystals, to the best of our knowledge. The synthesized materials demonstrate red emission due to the⁵D0–⁷FJ transitions of Eu³⁺ upon 250 nm excitation into¹ππ* state of the terephthalate ion. Size reduction results in broad-ened emission bands, an increase in the non-radiative rate constants and a decrease in both the quantum efficiency of the⁵D0 level and Eu³⁺ and the luminescence quantum yields. Cu²⁺, Cr³⁺, and Fe³⁺ ions efficiently and selectively quench the luminescence of nanocrystalline europium(III) ter-ephthalate, which makes it a prospective material for luminescent probes to monitor these ions in waste and drinking water.