Mild-hydrothermal synthesis of RE(OH)SO₄ layered compounds (RE = La-Tb), crystal structure, thermolysis, and photoluminescence

A series of RE(OH)SO4 layered compounds (RE = La-Tb lanthanides) were successfully synthesized via hydrothermal reaction under near-neutral solution pH and the mild temperature of 180 degrees C for 24 h, and the temperature/pH/time courses of phase/morphology evolution were clarified with RE = Tb for example. The compounds were characterized in detail for crystallite morphology, crystal structure, thermal behavior and vibrational property, and the intrinsic influence of lanthanide contraction was unveiled. Tb(OH)SO4 was analyzed to be isostructural with its La-Gd analogues (CN = 9 for Tb), instead of the reportedly Dy-Yb ones (CN = 8), and have parameters of a = 4.3806 angstrom, b = 12.1729 angstrom, c = 6.7674 angstrom and beta = 106.3967 degrees for its monoclinic unit cell (P21/n space group). The Eu and Tb compounds exhibited red (lambda ex = 395 nm, lambda em = 616 nm) and green (lambda ex = 369 nm, lambda em = 545 nm) emissions, and have fluorescence lifetimes of 0.84 and 1.07 ms and chromaticity coordinates of around (0.632, 0.365) and (0.295, 0.481), respectively.