First principles calculations of optical properties for oxygen vacancies in binary metal oxides

Using an advanced computational methodology implemented in CP2K, a non-local PBE0-TC-LRC density functional and the recently implemented linear response formulation of the Time-dependent Density Functional Theory equations, we test the interpretation of the optical absorption and photoluminescence signatures attributed by previous experimental and theoretical studies to O-vacancies in two widely used oxides-cubic MgO and monoclinic (m)-HfO₂. The results obtained in large periodic cells including up to 1000 atoms emphasize the importance of accurate predictions of defect-induced lattice distortions. They confirm that optical transitions of O-vacancies in 0, +1, and +2 charge states in MgO all have energies close to 5 eV. We test the models of photoluminescence of O-vacancies proposed in the literature. The photoluminescence of V_O ⁺² centers in m-HfO₂ is predicted to peak at 3.7 eV and originate from radiative tunneling transition between a V_O ⁺¹ center and a self-trapped hole created by the 5.2 eV excitation.