Lanthanoids I 2800 A Simple Aqueous Metathesis Reaction Yields New LanthanideMonothiophosphates. -Two new rare earth monothiophosphate materials, LaPO 3 S·xH 2 O and NdPO3S·yH2O are precipitated from aq. solutions of LnCl3 (Ln: La, Nd) and Na3PO3S and characterized by powder XRD, SEM, DTA, TGA, diffuse reflectance UV/VIS/ NIR, and photoluminescence spectroscopy. Both compounds are similar to the orthophosphate mineral rhabdophane. The rhabdophane-type compounds show reversible dehydration and rehydration under mild conditions. The monothiophosphate hydrates displayed broad photoluminescence in the visible range under excitation by a 325 nm laser. -(TAKAS, N. J.; SLOMKA, L. E.; YANG, X.; GILES, N.; AITKEN*, J. A.;