Solid-state photoluminescence, energy transfer mechanism and optical band gap of two 4f-5d complexes with 1-D chain-like structure

Abstract

Under hydrothermal conditions, two novel lanthanide (III)-mercury (II) compounds [Ln (IA)3(H3O)2]2n·2n (HgCl4)·n (Hg2Cl5)·nH3O·3nH2O (Ln ​= ​Eu, 1; Tm, 2; HIA ​= ​isonicotinic acid) were synthesized. The single-crystal X-ray diffraction revealed that they are isostructural and they feature a one-dimensional (1-D) chain-like structure and a three-dimensional (3-D) supramolecular network. Solid-state photoluminescence experiments revealed that they show red or blue emission bands, which can be assigned to the characteristic emissions of the 4f electron intrashell transitions of 5D0 → 7FJ (J ​= ​1, 2, 3, and 4; Eu3+, 1) or 1G4 → 3H6 (Tm3+, 2), respectively. The energy transfer mechanisms were revealed by the energy level diagrams of the Eu3+ or Tm3+ ions and isonicotinic acid ligand. Both compounds exhibit remarkable CIE chromaticity coordinates of (0.6454, 0.3543) and (0.1092, 0.1497) for 1 and 2, respectively. Solid-state UV–Vis–NIR diffuse reflectance spectra uncovered that they possess wide optical band gaps of 3.16 ​eV and 3.18 ​eV for 1 and 2, respectively.