Preparation, structure and properties of a novel bimetallic erbium-mercury compound with upconversion photoluminescence

A novel two-dimensional (2-D) bimetallic erbium-mercury compound {[Er(IA)(HIA)2(H2O)2]2(Hg3Br8)}n(nHgBr2)·2nNO3 (denoted as 1; HIA = isonicotinic acid; IA = isonicotinato anion) was prepared and characterized. Compound 1 crystallizes in the space group P2/c of the monoclinic system. By using solid state samples, it was observed that there are three upconversion photoluminescence emission bands at 400 nm, 475 nm and 526 nm, of which the band at 526 nm is the strongest. These bands can be attributed to the 4F9/2 → 4I15/2, 4F7/2 → 4I15/2 and 2H11/2 → 4I15/2 transitions of the Er3+ ions, respectively. An energy transfer mechanism of the photoluminescence emission bands was described with the energy state diagram of the Er3+ ion and the isonicotinic acid molecule. Compound 1 is characteristic of CIE (Commission Internationale de I'Éclairage) chromaticity coordinates of 0.1479 and 0.4321 in the green region. Compound 1 shows a wide optical band gap of 2.39 eV.