The present chapter represents the determination of various optical constants (absorption coefficient, extinction coefficient, and optical band gap) in quaternary Se80In5Te15−xSbx chalcogenide thin films. Melt quenching technique was used to synthesize quaternary Se80In5Te15−xSbx alloys. The EDS spectrum and elemental mapping was performed for existence of wanted constituents in synthesized samples. Non-isothermal DSC measurements were done to confirm that the synthesized samples exhibited both amorphous and glassy states. The high-resolution X-ray diffraction (HRXRD) was also studied to confirm the amorphous nature of Se80In5Te15−xSbx chalcogenide glasses. The Photoluminescence studies of Se80In5Te15−xSbx thin films were investigated within the spectral range of 600–800 nm. The estimated optical band gap was observed to decrease, whereas extinction coefficient (k) and coefficient of absorption (α) enhance by increasing Sb contents in our studied samples.