Syntheses, structures, solid-state photoluminescence and optical band gaps of two novel heterometallic lanthanide/mercury compounds

Abstract

Two novel heterometallic lanthanide/mercury compounds [Ln (HIA)3(H2O)2]n (Hg3Cl9)n·4nH2O (Ln ​= ​Sm3+ (1), Dy3+ (2); HIA ​= ​isonicotinic acid molecules) have been prepared under hydrothermal conditions and the crystal structures were characterized using single-crystal X-ray diffraction technique. They are isostructures and are characterized by a one-dimensional (1-D) chain-like structure with two kinds of 1-D chains coexisting in the structure. Solid-state photoluminescence measurements revealed that both compounds display upconversion emission bands in the green and yellow region. The bands originate from the characteristic emissions of the 4f electron intrashell transitions of the 4G5/2 ​→ ​6H5/2 (Sm(III) ions in 1) and 4F9/2 ​→ ​6H13/2 (Dy(III) ions in 2). An energy transfer mechanism is explained with an energy level diagram of Sm(III) ions, Dy(III) ions and isonicotinic acid molecules. Compounds 1 and 2 have CIE (Commission Internationale de I’Éclairage) chromaticity coordinates of (0.3609, 0.4812) and (0.4453, 0.5512). The CCT (Correlated Color Temperature) are 4926 ​K and 3726 ​K for compounds 1 and 2, respectively. Solid-state UV/visible diffuse reflectance spectra revealed that compounds 1 and 2 have wide optical band gaps of 2.98 ​eV and 3.19 ​eV, respectively.