(Solid + liquid) equilibria for the ternary system (CsBr + LnBr3 + H2O) (Ln = Pr, Nd, Sm) at T = 298.2 K and atmospheric pressure, thermal and fluorescent properties of Cs2LnBr5·10H2O

Abstract

The (solid+liquid) phase equilibria of the ternary systems (CsBr+LnBr3+H2O) (Ln=Pr, Nd, Sm) at T=298.2K were studied by the isothermal solubility method. The solid phases formed in the systems were determined by the Schreinemakers wet residues technique, and the corresponding phase diagrams were constructed based on the measured data. Each of the phase diagrams, with two invariant points, three univariant curves, and three crystallization regions corresponding to CsBr, Cs2LnBr5·10H2O and LnBr3·nH2O (n=6, 7), respectively, belongs to the same category. The new solid phase compounds Cs2LnBr5·10H2O are incongruently soluble in water, and they were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs2PrBr5·10H2O, Cs2NdBr5·10H2O and Cs2SmBr5·10H2O in water were measured to be (52.49±0.48)kJ·mol−1, (49.64±0.49)kJ·mol−1 and (50.17±0.48)kJ·mol−1 by microcalorimetry under the condition of infinite dilution, respectively, and their standard molar enthalpies of formation were determined as being −(4739.7±1.4)kJ·mol−1, −(4728.4±1.4)kJ·mol−1 and −(4724.4±1.4)kJ·mol−1, respectively. The fluorescence excitation and emission spectra of Cs2PrBr5·10H2O, Cs2NdBr5·10H2O and Cs2SmBr5·10H2O were measured. The results show that the upconversion spectra of the three new solid phase compounds all exhibit a peak at 524nm when excited at 785nm.