A solid-solution of cerium-substituted alkaline earth scandium silicate phosphors, (Ba1−xSrx)9Sc2Si6O24:Ce3+,Li+ (x = 0, 0.25, 0.50, 0.75, 1), have been prepared by solid-state reaction. The structures, characterized using synchrotron X-ray powder diffraction, show the solid-solution closely follows Vegard's law. The substitution of Sr for Ba results in a decrease of the alkaline earth–oxygen bond distances by more than 0.1 Å at all three crystallographic sites, leading to changes in optical properties. The room temperature photoluminescent measurements show the structure has three excitation peaks corresponding to Ce3+ occupying the three independent alkaline earth sites. The emission of (Ba1−xSrx)9Sc2Si6O24:Ce3+,Li+ is red-shifted from the near-UV (λmax = 384 nm) for x = 0 to blue (λmax = 402 nm) for x = 1. The red-shifted photoluminescent quantum yield also increases when Sr is substituted for Ba in these compounds.