Study on the electronic structures and optical properties of Ca-doped KH2PO4 crystal

Abstract

The first-principles method has been used to investigate the impact of Ca substitution at K sites on the electrical structures and optical characteristics of KH2PO4 crystals. And we use the FNV correction approach for the finite-size system and the HSE06 hybrid functional to update the defect formation energy and fix the "band-edge" issue. The results of defect formation energy indicate that the defect CaK· is the easiest to form. Crystal properties may be more susceptible to damage. The valence band maximum (VBM) of CaK× is shifted downward and the conduction band minimum (CBM) is shifted downward. The VBM of CaK· and CaK·· is slightly shifted upward, and CBM is almost unchanged. But Ca-induced defect energy levels are responsible for bandgap reduction and conduction band bottom shift. The absorption peaks of PE-KDP and FE-KDP occur at 1.1 eV and 2.05 eV, respectively, when the electron transitions between the defect transition level and CBM. Conversely, the absorption maxima are located at 6.5 eV and 5.4 eV, correspondingly, when the electron makes a jump between the defect transition level and VBM. Stokes redshifts are 0.3 and 0.9 eV. It damages the crystal and lowers the irradiation resistance threshold by generating vibrational energy in the lattice. Avoid CaK for better KDP quality.