A judicious choice of the lanthanide cation and its content in the Na-3(y(1-a)M(a))Si3O9 (M=Tm3+, Tb3+; a=0-1) system allows the optical properties to be tuned over a very wide range. The materials have the same framework structure and encompass thulium-based blue- and infrared-emitters and terbium-based X-ray phosphors (see spectra in Figure). The emission can be controlled in some infrared regions by varying the Y3+/Tm3+ molar ratio.