Based on the investigation of phases present and luminescence of the system Sr-8[Si4xO4+8x]Cl-8: Eu2+, the correct formula for this material was determined as Sr-8[Si4O12]Cl-8:Eu2+ rather than Sr4Si3O8Cl4:Eu2+, which had been assumed previously. The structure of this material was refined by the Rietveld method using powder X-ray diffraction data, which has a tetragonal unit cell with space group I4/m, Z = 2, a = 1.11814(1)nm, c = 0.95186(1) nm. In this structure, Sr has one site; therefore, when Eu2+ is doped in, the luminescence gives only one broad emission peak.