Using the first-principle calculations of density functional theory within the (FP-LAPW) method, we have investigated the structural, electronic and optical properties of Bi₂Te_3-xSe_x alloys with compositions x = 0, 1, 2 and 3 of Se. The generalized gradient approximation functional of Wu and Cohen (GGA-PBE) is used to calculate ground state structural parameters of Bi₂Te_3-xSe_x , which are in good agreement with theoretical and experimental data. The electronic band structures and optical constants have been improved with Tran-Blaha modified Becker-Johnson (TB-mBJ) parameterization scheme. Also, we have analyzed in detail the performance of dielectric function, refractive index, reflectivity and optical conductivity of these alloys. Our results show that Bi₂Te_3-xSe_x alloys are promising candidates for optoelectronic applications especially in the Infrared and visible fields. Bi₂Te_3-xSe_x materials have a direct band gap and can be tuned from 0.1706 eV to 0.7819 eV by varying In composition so emission was tunable from 1.58 to 7.26 micrometers (infrared field), in addition for their direct band gap and in view of their attractive optical properties such conductivity, absorption and reflectivity these materials is considered as promising materials for optoelectronic applications.