Locating impurity and defect levels in the host band gap by first-principles calculations: Pure and Ce3+-doped YAlO3

The structural and electronic properties of the YAlO₃ crystal (neat, Ce³⁺-doped and with antisite defects) were calculated from the first-principles. Comparison of the calculated electronic band structures of the ideal YAlO₃ host with the YAlO₃:Ce³⁺ and YAlO₃ (antisite) cases allowed to determine the Ce³⁺ ground 4f state to be at 3.5 eV above the valence band top, in very good agreement with the Dorenbos model prediction. The complete energy level scheme of the YAlO₃:Ce³⁺ crystal was obtained, with the cerium crystal field split 4f and 5d levels superimposed onto the host's band structure. It was shown that the yttrium antisite ions produce localized defect levels 0.87 eV below the conduction band, which enables the antisite defects to serve as the trap centers for the electron excitation energy in this host.