Atomically thin materials have attracted attention because of their unique physical properties. Several two-dimensional (2D) materials have been synthesized and screened experimentally and theoretically. Among these, alkaline earth metal-based 2D materials exhibit unique physical properties and have numerous applications in electronics, optoelectronics, dentistry, and scintillators. In this study, the single layer of strontium iodide, a 2D alkaline earth metal halide, was investigated for its structural, electronic, and optoelectronic properties using density functional theory, and a comparative analysis was performed with other similar materials. These investigations also covered frequency- and polarizationdependent dielectric and optical functions. Substitutional doping with lanthanide series elements (Nd, Sm, and Ho) was performed. The obtained results indicate the significant role of these dopants in tuning electronic and optical quantities. The increased static refractive index of the doped materials indicates enhanced reflection owing to the backscattering of the incident light from the impurity atoms. The optical conductivity is significantly improved in the visible region. Our findings suggest that these monolayer materials have potential applications in visible light, ultraviolet-C, and vacuum ultraviolet absorbers, anti-reflection coatings, and highly reflective systems. Hence, these materials are excellent candidates for nanoelectronic and optoelectronic devices.