Cationic substitution demonstrates significant potential for regulating structural dimensionality and physicochemical performance owing to the cation-size effect. Leveraging this characteristic, this study synthesized a new family of K 4 AeP 2 S 8 (Ae = alkaline earth elements: Mg, Ca, Sr, and Ba) thiophosphates, involving the substitution of Ae 2+ cations. The synthesized compounds crystallized in distinct space groups, monoclinic P 2/ c (Ae = Mg) versus orthorhombic Ibam (Ae = Ca, Sr, and Ba), exhibiting intriguing dimensionality transformations from zero-dimensional (0D) [Mg 2 P 4 S 16 ] 8- clusters in K 4 MgP 2 S 8 to 1D ∞ [AeP 2 S 8 ] 4- chains in other K 4 AeP 2 S 8 thiophosphates owing to the varying ionic radii of Ae 2+ cations, Ae-S bond lengths, and coordination numbers of AeS n (Mg: n = 6 versus other: n = 8). Experimental investigations revealed that K 4 AeP 2 S 8 thiophosphates featured wide optical bandgaps (3.37-3.64 eV), and their optical absorptions were predominantly influenced by the S 3p and P 3s orbitals, with negligible contributions from the K and Ae cations. Notably, within the K 4 AeP 2 S 8 series, birefringence (Δ n ) increased from K 4 MgP 2 S 8 (Δ n = 0.034) to other K 4 AeP 2 S 8 (Δ n = 0.050-0.079) compounds, suggesting that infinite 1D chains more significantly influence Δ n origins than 0D clusters, thus offering a feasible approach for enhancing optical anisotropy and exploring potential new birefringent materials.