The optical properties of Eu-activated (Ba,Sr)(13-x)Al22-2xSi10+2xO66 materials have been determined after the structural reinvestigation of the hypothetical Ba13Al22Si10O66 material on the basis of the Gebert's model. The white fluorescence and phosphorescence of the (Ba,Sr)(13-x)Al22-2xSi10+2xO66:Eu series result from the existence of two broad emission bands associated with H-8-4f(6)5d(1) -> S-8-4f(7) transitions peaking at 534 and 438 nm, the intensities of which may be tuned at room temperature via the con trol of the europium concentration and the substitution of Sr for Ba. This suggests the possibility to adjust the emission of the material to white LED requisites.