Balancing the second-harmonic generation (SHG) coefficient, band
gap, and birefringence is a vital but addressable challenge for designing
infrared nonlinear optical materials. By applying a “rigidity–flexibility
coupling” strategy, a quaternary diamond-like phosphide, Mg2In3Si2P7, with wurtzite-type
superstructure was successfully designed and synthesized. Remarkably,
it achieved the rare coexistence of giant second-harmonic generation
(2 × ZnGeP2 and 7.1 × AgGaS2), suitable
band gap (2.21 eV), moderate birefringence (0.107), and wide IR transparent
range (0.56–16.4 μm). First-principles calculations revealed
that the giant SHG response and large birefringence can be attributed
to the synergy of arrangement-aligned [InP4] and [SiP4] tetrahedra. This work not only opens a new avenue for designing
advanced infrared nonlinear optical materials but also may spur more
explorations on quaternary diamond-like pnictides.
To design pnictide nonlinear optical materials with wide band gap and large second‐harmonic generation, the heavy halogen I was introduced into pnictides through anionic aliovalent substitution with diamond‐like ZnS as templates. Thus, four excellent halopnictide‐based infrared nonlinear optical crystals, MII3PnI3 (MII=Zn, Cd; Pn=P, As), were obtained. They all exhibited defect diamond‐like structures with highly parallel‐oriented [MIIPnI3] mixed‐anionic tetrahedral groups, leading to excellent physical properties including wide band gaps (2.38–2.85 eV), large second harmonic generation responses (2.7–5.1×AgGaS2), high laser‐induced damage thresholds (5.5–10.7×AgGaS2), and good IR transparency. In particular, Cd3PI3 and Cd3AsI3 achieved phase‐matching (Δn=0.035 and 0.031) that their template β‐ZnS could not do. Anionic aliovalent substitution provides a feasible strategy to design novel promising halopnictide IR NLO materials.
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