Solid–Liquid Equilibria of the Ternary System CsBr–REBr3–H2O (RE = La, Ce) at 298.15 K, Thermal Properties of Cs2REBr5·10H2O, and Fluorescent Properties of Cs2CeBr5·10H2O

Abstract

Solubilities were studied for the ternary systems of CsBr–LaBr3–H2O and CsBr–CeBr3–H2O at 298.15 K using the isothermal solubility method; the corresponding phase diagrams were constructed. The solid phases were determined by the Schreinemakers wet residues technique. Three solid phases of CsBr, Cs2LaBr5·10H2O, and LaBr3·7H2O in the system CsBr–LaBr3–H2O, and those of CsBr, Cs2CeBr5·10H2O, and CeBr3·7H2O in the system CsBr–CeBr3–H2O were obtained, respectively. The compounds Cs2LaBr5·10H2O and Cs2CeBr5·10H2O are incongruently soluble in water. The new solid phase compounds Cs2LaBr5·10H2O and Cs2CeBr5·10H2O were characterized by chemical analysis, X-ray diffraction and thermogravimetric/differential thermogravimetric techniques. The standard molar enthalpies of solution of Cs2LaBr5·10H2O and Cs2CeBr5·10H2O in water were measured to be (49.61 ± 0.37) kJ·mol–1 and (50.83 ± 0.46) kJ·mol–1 by microcalorimetry under the condition of infinite dilution, and their standard molar enthalpies of formation were determined as being −(4739.3 ± 1.3) kJ·mol–1 and −(4729.6 ± 1.5) kJ·mol–1. The fluorescence excitation and emission spectra of Cs2CeBr5·10H2O were measured. The results show that upconversion spectra of Cs2CeBr5·10H2O exhibit at 524 nm and 697 nm excited at 785 nm, and the intensity of the emission spectra at 524 nm is stronger than that at 697 nm. This research can provide fundamental data for the rare earth industry and future study. The phase diagrams of the ternary systems could provide the fundamental basis and serve as a guide for the preparation of Cs2LaBr5·10H2O and Cs2CeBr5·10H2O.