Electronic structures and optical spectra of KDP crystals with Sp doping defects: a first-principles study

In order to further clarify the effect of sulfur doping on the laser damage threshold of potassium dihydrogen phosphate (KDP), the properties of sulfur substituting for phosphorus doping defects (S_P) in KDP crystals with paraelectric (PE) and ferroelectric (PE) phases are studied in this article. More accurate defect transition levels were obtained by band edge correction, and the band edge corrected values were 1.28 eV and 1.88 eV for the PE and FE phases, respectively. The defect formation energies with four different defect charges (0, +1, +2, and-1) were obtained using the finite size correction scheme. The stable defect charge states were (+2 charge state) (+1 charge state) and (-1 charge state) in turn when the Fermi level moved from the valence band maximum (VBM) to the conduction band minimum (CBM). Moreover, by considering the electron-phonon coupling, the optical absorption and emission spectra were obtained. The absorption peak for the state of the PE phase at 4.63 eV was close to the experimental value. We predicted that the absorption peak at 4.50 eV belongs to the state with the FE phase. The emission peaks at 0.10 eV and 1.36 eV were related to the PE and FE phases, accordingly. The absorption may affect the application of S-KDP crystals and reduce the laser damage threshold.