Two new alkali bismuth silicates were prepared via high temperature flux crystal growth and their structures characterized by single crystal X-ray diffraction (SXRD). Cs3BiSi8O19 and Cs4Bi2Si8O21, crystallize in the orthorhombic space groups Pnma (a = 11.5903, b = 7.0346, c = 26.7393) and Pnn2 (a = 14.2674, b = 33.8270, c = 7.24260) respectively. Cs3BiSi8O19 was modified via ion exchange (K for Cs) and Cs4Bi2Si8O21 via Eu doping in a flux environment yielding Cs0.79K2.21BiSi8O19 and Cs4Bi1.72Eu0.28Si8O21, respectively. The two phases crystallize in the orthorhombic space group Cmcm and the monoclinic space group P21/n, respectively. Photoluminescence measurements demonstrated that the europium doped Cs4Bi1.72Eu0.28Si8O21 exhibited emission corresponding to the 5D0 → 7F2 (613 nm) red emission and 5D0 → 7F1 (590 nm) orange emission, characteristic of Eu3+ f-f transitions.