First-principles study on the KDP crystals with point defect Tip

Abstract Potassium dihydrogen phosphate (KDP) crystals are widely used in high-power laser systems. Their laser-induced damage threshold (LIDT) limits the maximum output power. Previous studies show impurities significantly affect the LIDT of KDP crystals. Based on first-principles calculations, this study systematically investigates the defect formation energies, lattice distortions, electronic density of states, and optical spectra of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> </mml:msub> </mml:math> defects with three distinct charge states (+1, 0, −1) in KDP crystals. The computational results reveal that <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>,</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> defects exhibit relatively low formation energies within the bandgap regions of both F-KDP and P-KDP crystals. The defect <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> </mml:msub> </mml:math> produces lattice distortion and alters bond lengths around the defect. Notably, the H-O bonds demonstrate significant structural distortion, exhibiting maximum bond length variations of 26.39%. Both <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>×</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> defects introduce spin-polarized defect levels within the band gap for the F-KDP and P-KDP crystals. The defect energy levels are primarily composed of Ti 3 d and O 2p orbital contributions. Furthermore, these defect energy levels facilitate multiphoton transition processes. The absorption and emission spectra constructed in this work incorporate electron–phonon coupling effects. The absorption spectrum peaks at 224 nm, which closely matches the experimentally observed value. THE existence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Ti</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">P</mml:mi> </mml:mrow> </mml:msub> </mml:math> defects will affect the LIDT of KDP crystals.