First-principles investigation of reduced KDP crystal damage threshold: defect clusters in Mg-related configurations

Abstract

In this study, we utilized first-principles methods to delve into defect clusters within potassium dihydrogen phosphate (KDP) crystals, focusing on (Mg_K + V_K) and (Mg_K + V_H) configurations. We examined their stability, defect formation energy, lattice distortion, electronic structures, and optical properties in both paraelectric (PE-KDP) and ferroelectric (FE-KDP) phases. In the PE phase, compensation of was accomplished via the nearest neighbor . Conversely, in the FE phase, compensation of was achieved utilizing the next nearest neighbor . Notably, the Mg–O ionic bond displayed significant changes in bond length, with a maximum alteration of 60%, as neighboring oxygen atoms moved closer to the magnesium atom. Furthermore, both structures displayed a downward shift of the conduction band minimum (CBM), primarily due to contributions from Mg 3s and O 2p orbitals, resulting in a reduction in the band gap. By analyzing the photoluminescence process alongside electron–phonon coupling phenomena, absorption and emission spectra were obtained. In the absorption spectra, peaks for PE-KDP and FE-KDP were observed at 335 nm and 386 nm, respectively, consistent with experimental observations of absorption at 355 nm. Upon exposure to a 355 nm laser, local crystal absorption led to a progressive increase in temperature, consequently lowering the damage threshold.