The synthesis and structural characterization of the first examples of microporous europium(III) and terbium(III) silicates (Na4K2X2Si16O38. 10H(2)O, X = Eu, Tb) are reported. The structure of these solids was solved by powder X-ray diffraction ab initio (direct) methods and further characterized by chemical analysis (EDS). thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Na-23 and Si-29 magic-angle spinning (MAS) NMR, and luminescence spectroscopy. Both materials display interesting photoluminescence properties and present potential for applications in optoelectronics. This work illustrates the possibility of combining in a given silicate microporosity and optical activity.