LAUSR

The defect formation energy of an oxygen vacancy with different charge states (0, +1, +2) has been studied. The finite-size correction scheme (FNV) for the alignment of the defect formation energy is available. The corresponding correction energies are in the range of 0.32–1.29 eV. On the basis of the corrected defect formation energy, fairly accurate optical spectrum line shapes of F and F+ centers are obtained, taking account of electron–phonon coupling. The calculated absorption and luminescence peaks are located at 2.73 eV and 2.62 eV for the F center, and 2.44 eV and 2.25 eV for the F+ center, respectively, which agree well with experimental results. Finally, the result proves that the F+ center is the key point involved in the body color change of the KNbO3 crystal.