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Al 2 O 3 and Al 2−x Cr x O 3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL * a * b * color data). The obtained results allow to identify the γ -Al 2 O 3 to α-Al 2 O 3 phase transition. The single-phase α-Al 2 O 3 powder was obtained after heat treatment at 1050 • C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al 2−x Cr x O 3 are related to the γ to α-Al 2 O 3 phase transition and the temperature S. Cava ( ) •

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Photoluminescence (PL) properties at room temperature of disordered Ba0.50Sr0.50(Ti0.80Sn0.20)O3 (BST:Sn) thin films were obtained by the polymeric precursor method. X-ray diffraction data and corresponding PL properties have been measured using the 488nm line of an argon ion laser. The PL spectra of the film annealed at 350°C for 21h are stronger than those of the film annealed at 350°C for 28h, indicating a disorganized structure. The energy band gaps of the crystalline and amorphous BST:Sn thin films were 3.35 and 2.25eV, respectively. The doped BST thin films also tend to a cubic structure, resulting from TiO6 deformations.