摘要: Thin films of Se87.5Te10Sn2.5 were prepared by vacuum thermal evaporation technique. Various optical constants calculated for the studied composition. The mechanism absorption follows rule direct transition. It was found that energy gap (Eg) decreases from 2.26 to 1.79 eV with increasing annealing temperature 340 450 K. This result can be interpreted Davis and Mott model. On other hand, maximum value refractive index (n) is shifted towards long wavelength temperature. In addition, high frequency dielectric constant (eL) increased 31.26 48.11 whereas ratio free carriers concentration its effective mass N/m n