The effect of alpha particles on the concentration of optical active oxygen in silicon samples doped with platinum was studied in this work and the radiation defects that appear after irradiation with alpha particles were determined. Silicon samples were doped with platinum, followed by irradiation with alpha particles with an energy of 2 MeV, the dose was 5•1014 cm-2. Some Peaks were detected indicating the presence of various types of chemical bonds. It was determined that the introduction of platinum atoms leads to a decrease in the concentration of optically active oxygen in silicon (almost 2 times), but after irradiation with alpha particles the oxygen concentration increases. Using spectroscopic ellipsometry, the layer thicknesses were determined, which changed after doping and irradiation.