Theoretical prediction of cluster configuration transitions and electro-optical properties of Y _P defects in KH ₂ PO ₄ <i>via</i> density functional theory

The corrected defect formation energies, crystal structures, electronic behaviors, and optical properties of Y_P isolated defects and Y_P + V_O cluster defects were studied using density functional theory. Results indicate that configuration transitions of point defects and cluster defects are encouraged under different oxygen partial pressures. Unlike Fe³⁺ or Cr³⁺, the defect formation energy of the Y_P defect center compensation by the nearest-neighbor V_O is the lowest, suggesting that under oxygen-poor conditions, the defect cluster of the Y_P defect composed of the nearest-neighbor O vacancy may be the main type of yttrium-like trivalent rare-earth metal atomic impurity in the crystal. Electronic behaviors show that the stronger coupling strength between the rare-earth metal Y and O and the bonding between H and O are the main reasons for the difference in the ease of formation of different defect cluster structures. Thus, the interatomic interactions between the [Y_P + V_O] cluster and the isolated defect were analyzed, and an attempt was made to explain certain experimental phenomena. Finally, their optical properties were determined, and the more pronounced defect levels and larger Stokes redshift indicated that cluster structures had a greater impact on the thermodynamic absorption of the crystal. New understanding has been gained regarding the effects of laser pre-treatment on KDP crystals. This suggests that an oxygen-rich atmosphere may improve the LIDT of KDP crystals containing trivalent rare-earth metal impurities, providing a theoretical basis for enhancing the optical properties of the crystal.