Synthesis and optoelectronic properties of three Eu(III)-dipicolinate complexes based on α-picolinic acid, 2-aminopyridine and 2-hydroxypyridine as secondary ligands

Abstract

We synthesized some Eu(III) complexes {[Eu(dpa)(α-pc)(CH3OH)]·2CH3OH} (1), {[Eu(dpa)(2-ap)(CH3OH)]·2CH3OH}(2) and {[Eu(dpa)(2-hp)(CH3OH)]·2CH3OH}(3) [dpa = dipicolinic acid; α-pc = α-picolinic acid; 2-ap = 2-aminopyridine; 2-hp = 2-hydroxypyridine]. The structural characterization of the complexes were studied by elemental analysis, FTIR spectroscopy, SEM and powder X-ray diffraction studies (XRD) where the elemental analysis and FTIR results indicate the coordination of ligands with the Eu(III) ion. The X-ray diffraction patterns show the crystalline nature of complex (1) and amorphous nature of complexes (2) and (3) and the SEM micrographs also depict different morphologies of the complexes. The thermal properties of the synthesized complexes were studied by TG–DTA technique which indicates good thermal stability of the synthesized complexes. The optical properties were studied using Ultraviolet visible spectroscopy (UV–Vis) and Photoluminescence studies (PL) where photoluminescence measurements indicate that all the three complexes exhibit the characteristic emission bands of Eu(III) ion corresponding to 5Do → 7FJ (J = 0–4) transitions and it has also been observed that the intensity of emission is influenced by the effect of different secondary ligands. The most intense transition and the long radiative lifetime, quantum efficiency of the 5Do excited level of Eu(III) ion observed for the complex (2) with 2-ap as secondary ligand reflects the good sensitizing ability of ligand 2-ap. The optical properties of the obtained complexes can be well utilized for preparation of rare earth luminescent materials and fluorescence probes.