Extendible synthesis of NaLnW2O8?2H2O (Ln=Sm-Lu, and Y) via one-step hydrothermal reaction: Phase, morphology and luminescence

The Hydrous lanthanide (Ln) double tungstates of NaLnW2O8.2H2O in orthorhombic structure have been directly produced by hydrothermal reaction of Na2WO4 and Ln(NO3)3 at pH=8 for 24 h under 200 degrees C for the small ions of Ln = Tm-Lu, under 150 degrees C for the slightly larger lanthanides of Ln = Ho, Y and Er, and under 100 degrees C for the even larger lanthanides of Sm-Dy. Moreover, NaLnW2O8.2H2O for Ln = Eu-Dy can also be synthesized at a slightly higher reaction pH of 9 at 150 degrees C, while it was failed for the other members in the lanthanide series of La-Nd even though various efforts were attempted in hydrothermal conditions. On the basis of the crystal structure of NaLnW2O8.2H2O and lanthanide contraction, this outcome conformed well to Pauling rules. Taking Ln = Lu for example, the phase evolution and morphology were studied by the combined techniques of XRD, FE-SEM, IR and TG/DSC. The photoluminescence properties of NaEuW2O8 center dot 2H2O and NaTbW2O8 center dot 2H2O, including excitation/ emission, CIE chromaticity, quantum yields, and fluorescence decay were characterized.