Display omitted •We calculate XPS and absorption spectra for crystalline HfO2 in frame of hybrid DFT.•We got the experimental XPS for bombarding with Ar-ions hafnia and HfOx.•Oxygen vacancies in HfO2 produce the defect states at 3.0eV above the valence band.•Ar+ ion bombardment of HfO2 produces the oxygen vacancies and polyvacancies.•Absorption peak at 3.0–4.5eV for HfO2 is attributed to the oxygen vacancy. The electronic structure of oxygen vacancies and polyvacancies in HfO2 was studied theoretically from the first-principles calculations and experimentally, by X-ray photoelectron spectroscopy. The electronic structure calculations of crystalline HfO2 were performed within the hybrid density functional theory. The experimental photoelectron spectra indicate that both nonstoichiometric chemistry and Ar-ion bombardment of hafnia films lead to the generation of the defect states at 3.0eV above the valence band. According to the calculations, these defect states are attributed to the oxygen vacancies.