Photoluminescence and semiconductive properties of a 4f–5d compound

Abstract

A novel 4f–5d compound [Ho(H2O)2(μ-IA)3Hg3Br6]n (1, HIA = isonicotinic acid) was prepared. It is characterized by single-crystal X-ray diffraction. The title compound crystallizes in the space group P21/n of the monoclinic system. The holmium ion is coordinated by six oxygen atoms to yield a slightly distorted tetragonal antiprism configuration. Three crystallographically independent mercury ions exhibit two different coordination environments, i.e., tetrahedron geometry and square pyramidal configuration. In the title compound, there are two types of one-dimensional (1D) chains, namely Hg–Br chains and Ho–IA chains. Both chains are interconnected by the μ3-bridging isonicotinic acid ligands to form a three-dimensional (3D) frame structure. Photoluminescence from solid samples showed that the title compound could emit up-conversion red fluorescence, and its half-peak width was about 14 nm. The emission peak comes from its characteristic emission of 5F5 → 5I8 of Ho3+. The CIE color coordinates of the title compound are (0.693, 0.307). The title compound displays a broad semiconductor gap being of 2.47 eV, as discovered by the solid-state diffuse reflection. A novel 4f–5d compound has been prepared. It features a 3D framework structure. It displays a red up-conversion photoluminescence emission band. Diffuse reflection spectrum with solid-state sample shows that it possesses a wide optical band gap of 2.47 eV.