• • Cd3.5PS6 exhibits an 8.5-fold increase in [CdS4] tetrahedral distortion over Cd4GeS6, yielding a 2 × AGS SHG response at 2050 nm and an LIDT of 9.4 × AGS; this directly addresses the low damage threshold of commercial AgGaS2 (LIDT ~2–3 × AGS) for high-energy mid-IR laser systems.
• • Hg0.5Cd3PS6 achieves a 2.73 × AGS SHG response at 2050 nm with an LIDT of 5 × AGS and birefringence of 0.076 at 2050 nm, enabling phase-matching in the 3–5 μm atmospheric window without the two-photon absorption that plagues ZnGeP2 at 2 μm.
• • The 2.66-fold distortion enhancement from Cd3.5PS6 to Hg0.5Cd3PS6 demonstrates that equivalent Hg2+ substitution concentrates Cd2+ vacancies at the Cd(2) site, providing a tunable structural knob for optimizing the trade-off between SHG efficiency and LIDT.
• • The defective DL strategy yields a 2.73 × AGS SHG response while maintaining an LIDT 5 times that of AGS, overcoming the historical inverse relationship between nonlinearity and damage threshold in chalcopyrite-type mid-IR materials.