Study on structure and fluorescence of Tb-doped CaAl LDHs prepared in ethanol/water system

Abstract

An important material applied in biological fluorescent detector and medical treatment is highly desired in view of the biocompatibility and fluorescent property. Here, Tb-doped CaAl-layered double hydroxides with Ca2+/(Al3+ + Tb3+) molar ratio of 1.0, 2.0, 3.0, and 4.0 have been successfully prepared in a mixed solution of ethanol and water in a reasonable proportion. Chemical compositional analyses revealed that the experimental value of Ca2+/(Al3+ + Tb3+) molar ratio present in the samples was close to the initial value of Ca2+/(Al3+ + Tb3+) molar ratio of raw reactants. In the X-ray diffraction results, it was found that the typical layered double hydroxides structure can be kept between the Ca2+/(Al3++Tb3+) molar ratio of 1.0 and 4.0. The structural type of the Tb-doped CaAl-layered double hydroxides was monoclinic form when the Tb content was less than of 3.0 %, while rhombohedral form appeared and retained as the content of Tb3+ is kept between 3.0 and 5.28 wt%. Photoluminescence shows strong green emissions attributed to 5D4-7FJ (J = 3, 4, 5, 6) transition of Tb3+ ions incorporated in the Tb-doped CaAl-layered double hydroxides. A series of Tb-doped CaAl-LDHs with different molar ratio of Ca2+/(Al3+ + Tb3+) have been synthesized by co-precipitation in a mixed ethanol/water system. Strong green emission appeared in the Tb-doped CaAl-LDH. The Tb–CaAl-LDHs may be a promising biological fluorescent material because of the biocompatibility of Ca2+ ions as well as the fluorescent property of Tb3+ ions.