Vacancy‐Induced Extraordinary Second Harmonic Generation Response for Diamond‐Like Cu3PS4

Improving polarizability is an important strategy for designing high‐performance mid‐infrared (mid‐IR) nonlinear optical (NLO) materials. The substitution of equivalent or aliovalent atoms can manipulate the polarizability by adjusting the symmetry of the polyhedron. Herein, the Li+ and Cd2+ are introduced into the Cu3PS4 as the equivalent and aliovalent dopants for the Cu site. As a result, Li+ can significantly improve the bandgap (Eg) of LixCu3−xPS4 from 2.38 to 2.88 eV, leading to a higher laser‐induced damage threshold (LIDT) of 4.9 times than AgGaS2 (AGS) with a comparable second harmonic generation (SHG) response of AGS (26−45 µm). Interestingly, Cd2+ can improve the SHG response and enlarge the Eg simultaneously. As a result, Cd0.4Cu2.2PS4 has a large SHG response of 10 × AGS at 2050 nm (26−45 µm) and a LIDT of 2.6 × AGS. Theoretical calculations reveal that lattice vacancies induced by Cd2+ significantly boost polarizability compared to LixCu3−xPS4 with no vacancy, leading to a strong NLO response. The lattice vacancies manipulation is realized by introducing the aliovalent Cd atom in Cu3PS4 for the first time. Compared to the LixCu3−xPS4, the CdxCu3−2xPS4 displays stronger second harmonic generation (SHG) response gradient enhancement with lattice vacancies content. Eventually, the Cd0.4Cu2.2PS4 possesses a high SHG response of 10 × AGS at 2050 nm and laser‐induced damage threshold (LIDT) of 2.6 × AGS.