Photoluminescence (PL) properties at room temperature of disordered Ba _0.50 Sr _0.50( Ti _0.80 Sn _0.20) O ₃ (BST:Sn) thin films were obtained by the polymeric precursor method. X-ray diffraction data and corresponding PL properties have been measured using the 488 nm line of an argon ion laser. The PL spectra of the film annealed at 350 ° C for 21 h are stronger than those of the film annealed at 350 ° C for 28 h , indicating a disorganized structure. The energy band gaps of the crystalline and amorphous BST:Sn thin films were 3.35 and 2.25 eV , respectively. The doped BST thin films also tend to a cubic structure, resulting from Ti O ₆ deformations.