Effect of the defect LaP in KDP crystals: first-principles study

Abstract

This study used DFT calculations to examine defect formation energy in potassium dihydrogen phosphate (KDP) with La substituting P. We found that neutral defects and the −3 charged state of La_P are more stable in the crystal. Lattice distortion analysis showed that defects disrupt the crystal structure. The H–O bond attached to the defect centre is shortened by 18.75–18.81%, resulting in HPO₄²⁻, which shares an H atom with the defect centre, becoming a hole trap and inducing more intrinsic defects. La_P point defects introduce new defect energy levels in the forbidden band, promoting defect energy level-assisted multiphoton absorption. By analysing the configuration coordinate diagram (CCD) and absorption spectrum, La^×_P introduces an absorption peak at 415 nm in the visible region, which is in accordance with the experimental results, showing a significant decrease in transmittance of La-doped KDP. The improvement in crystal transmittance after γ-ray irradiation is attributed to the transition of defects from La^×_P to , resulting in a red-shifted absorption spectrum in the ultraviolet region with a peak at 289 nm. This process produces a large Stokes redshift, which can lead to local melting of the crystal and greatly reduce the optical properties of the crystal.