Influence of Cr3+ cluster defects on crystal structure and optical properties of KDP crystals studied by DFT and UV-Vis

Abstract

Cr³⁺ ions are impurity cations that lower the laser-induced damage threshold of crystals. Herein, the stability of Cr³⁺ cluster defects and their effects on crystal structure, electronic structure and optical properties were examined by DFT and UV-Vis spectroscopy. Two stabilizing Cr_K²⁺ + 2V_H⁻ cluster configurations were constructed using first-principles calculations for the point defect where Cr³⁺ ions are substituted for K⁺ ions. Cluster defects lead to large deformations in the O–H bonds of KDP crystals and introduce multiple defect states in the crystal band gap. Due to the absorption between impurity energy levels and the entire energy band, Cr³⁺ ions cause optical absorption in the crystal at 285 nm, 451 nm and 650 nm. Cr³⁺ ions cause additional energy to be absorbed during laser irradiation of the KDP crystals, which in turn adversely affects the laser-induced damage threshold of the crystal. Our data indicate that the laser-induced damage threshold of the KDP crystals can be increased by decreasing the concentration of the cluster defects in the KDP crystals.