Electronic structures and optical properties of defective KDP with V-doped: A first-principles study

The effect of V single-doping on the defect formation energies, electronic structures, and optical properties of potassium dihydrogen phosphate (KH2PO4, KDP) crystals in tetragonal and orthorhombic phases has been investigated using first-principles calculations based on density functional theory (DFT). Meanwhile, we apply the HSE06 hybrid functional to correct the "band-edge" problem as well as the FNV correction method for the finite-size system to revise the defect formation energy. Our research reveals that V doping could lead to a marked expansion of the lattice at the defect sites, making the crystal susceptible to damage. The band gap of the V-KDP crystals is smaller than that of the perfect KDP crystals because the V-3d orbitals hybridize with the O-2p orbitals to create defective energy levels at the conduction band minimum (CBM). Furthermore, we used configuration coordinate diagrams (CCD) and optical spectra to analyze the optical properties of V defects and found absorption peaks at 6.01 eV (206 nm) in tetragonal KDP and 5.68 eV (218 nm) in orthorhombic KDP. The calculation results indicate that the quality of the KDP crystals can be enhanced by reducing the concentration of V-impurities, which can serve as a theoretical guide for the practical application of KDP.