Oxygen vacancies in KTiOPO4: Optical absorption from hybrid DFT

Density functional theory is used to calculate the optical absorption of oxygen vacancies in potassium titanyl phosphate (KTiOPO4, KTP) crystals. A modified hybrid functional is used for the description of the midgap defect states and the optical excitation energies. Oxygen vacancies in the +2 charge state lead to rather minor modification of the bulk KTP optical response, while the +1 and neutral charge states give rise to characteristic midgap optical absorption covering the whole near-infrared and visible spectrum. Its intensity is strongly polarization dependent and strongest for light polarized parallel to the z axis. The modification of the KTP optical absorption by oxygen vacancies predicted here corroborates the picture that the gray-track formation in KTP, i.e., its photochromic damage, is related to a successive charging of oxygen vacancies.

Automated summary

In this study, density functional theory was applied to calculate the optical absorption of oxygen vacancies in potassium titanyl phosphate (KTP) crystals. The results showed that the presence of oxygen vacancies significantly influenced the optical absorption properties of the crystals, particularly in the +1 and neutral charge states, where midgap optical absorption was observed within the near-infrared and visible spectrum.