Photoluminescence and semiconductor properties of two novel lanthanide-mercury compounds with one-dimensional chain-like structures

Two novel lanthanide-mercury compounds [Ln(IA)3(H2O)2]n(Hg3Cl9)n·4nH2O (Ln = Eu (1) and Tb (2); IA = isonicotinic acid) have been synthesized under solvothermal conditions and structurally characterized by single-crystal X-ray diffraction. Both complexes exhibit one-dimensional (1D) chain-like structure with a novel isolated (Hg3Cl9)3– anion. Solid-state diffuse reflectance spectroscopy reveals the presence of wide optical band gaps of 2.81 eV and 3.47 eV, suggesting that they are potentially wide band gap organic semiconductor materials. Solid-state photoluminescence measurements uncover that they show red or green light emission bands, respectively. The emission bands can be assigned to the characteristic emission of the 4f electrons intrashell transitions of 5D0 → 7FJ (Eu3+, J = 2 and 4) and 5D4 → 7FJ (Tb3+, J = 6, 5, 4 and 3), respectively. Energy transfer mechanism is explained by the energy level diagram of Eu3+ ion, Tb3+ ion and isonicotinic acid ligand. The title compounds have remarkable CIE chromaticity coordinates of (0.6438, 0.3559) and (0.3172, 0.4773). This suggests that they may be potential candidates with red or green light emitting materials for white light emitting diodes (LEDs).