Abstract
The magnetic signatures of centers in potassium titanyl phosphate (KTP) are studied within density-functional theory (DFT). The hyperfine tensor elements are very sensitive to the structural surrounding; the paramagnetic hyperfine splittings are used to evaluate the defect models. For each of the four experimentally observed electron paramagnetic resonance (EPR) spectra, we identify a defect model that reproduces the paramagnetic signature. All of them are electron donors, whereby one specific Ti atom can be identified, whose formal oxidation number is lowered from in the ideal crystal to . The related charge redistribution leads to a strong polarization of the corresponding center. However, in three cases a second Ti atom, connected to the first by a mutual polarized O atom, is polarized too. Positively charged O vacancies at the lattice site O(10) are unique in leading to the formation of the only center that is stable at room temperature. This defect induces a defect state within the band gap, which may be excited during second harmonic generation (SHG) applications and thus is a plausible candidate to explain the so-called gray tracking, i.e., photochromic damage.
- Received 2 October 2020
- Revised 13 November 2020
- Accepted 17 November 2020
DOI:https://doi.org/10.1103/PhysRevMaterials.4.124402
©2020 American Physical Society