Metal oxide semiconductors with distinctive optical and electrical properties are required by the modern electronics industry. In this research, it was found that doping with transition and rare-earth metals is suitable for tuning the optical band gap and dielectric parameters of tin (IV) oxide (SnO2) nanoparticles (NPs) to meet the requirement for highly conductive semiconductors through one-step hydrothermal synthesis. Doping with samarium (Sm) results in tin (IV) oxide NPs having a narrower band gap (2.54 eV) than pure tin (IV) oxide NPs (3.36 eV) and increased conductivity at higher frequencies and temperatures, which are crucial for potential applications such as light-emitting diodes, biological labels and optoelectronic devices. The particle size of the doped and co-doped samples was found to be smaller than that of pure tin (IV) oxide, which effectively enhanced the quantum confinement effect in these metal oxides. Co-doping samarium-copper (Cu) ions into the tin (IV) oxide lattice was done for the first time to increase the dielectric strength, with the absorption shift toward the visible blue region suggesting the use of this particular sample for photocatalytic application.