The band gap engineering studies have grabbed enormous attention from scientists due to offering modification for the band gap of interested materials. This study exhibits that Os with different atomic percentages (1 and 5 mol %) can replace the Fe sites. Furthermore, it has been realized that the band gap of YbFO can be lowered slightly via Os doping from 2.10 eV to 2 eV for 1 mol % Os doped compounds and it goes slightly up to 2.12 eV for 5 mol % Os substituted sample. The optical features such as optical dielectric constant, conductivity, index (n), extinction coefficient (k), reflectance % and transmittance % of Os doped YbFO thin films were scrutinized by diffuse reflectance spectroscopy (DRS). It is noticed that the reflectance % rises as the Os dopant ratio goes up. For instance, the reflectance % of YbFO is similar to 20 at the wavelength of 650 nm, whereas, it becomes similar to 47 at the same wavelength value. Furthermore, it has been shown that the refractive index n advances from 3 for YbFO up to 6 for 5 mol % Os doped sample at 1.9 eV photon energy. It has been exhibited that the extinction coefficient k of 5 mol % doped compound has the lowest values among the studied samples. For example, k is around 0.1 for the undoped compound, yet, it drops to about 0.025 for 5 mol % Os substituted specimen at 1.9 eV. It has been also demonstrated that the real part of the optical dielectric constant increases as Os dopant level goes up. For instance, it is around 8 for YbFO and it becomes close 35 when the photon energy is 1.9 eV. It should be mentioned that as the photon energy is further ramped up, the real part of the dielectric constant for the investigated samples decreases and it becomes around 3 at 3.8 eV. When the real part of the conductivity is taken account, it is seen that 5 mol % Os doped YbFO sample has the lowest conductivity value compared to other samples. It is 1x10(4) S/m for 5 mol % sample and it becomes similar to 1.6x10(4) S/m for the undoped sample. Moreover, Photoluminescence (PL) spectroscopy studies have revealed that 5 mol % substituted compound has the highest oxygen vacancies compared to other samples. Raman spectroscopy investigation has unveiled that the samples have similar space group.