Second-Harmonic Generation-Positive Na 2 Ga 2 SiS 6 with a Broad Band Gap and a High Laser Damage Threshold.

The development of high-power solid-state lasers is in urgent need of new infrared nonlinear optical (IR NLO) materials with a wide band gap and a high laser-induced damage threshold. A new infrared nonlinear optical material Na 2 Ga 2 SiS 6 has been synthesized for the first time, crystallizing in the Fdd 2 (no. 43) noncentrosymmetric space group. Its three-dimensional tunnel framework consists of two typical NLO active motifs [GaS 4 ] and [SiS 4 ], with Na + cations located inside the tunnels. Na 2 Ga 2 SiS 6 exhibits comprehensive optical properties, namely, a wide transmission range, a high laser-induced damage threshold (10 × AgGaS 2 ), a type-I phase-matching second-harmonic generation response (0.2 × AgGaS 2 ), and especially a wide band gap (3.93 eV), which is the largest in the A 2 M III 2 M IV Q 6 (A = alkali metals; M III = IIIA elements; M IV = IVA elements; Q = S and Se) family. Therefore, Na 2 Ga 2 SiS 6 does not produce two-photon absorption under a 1064 nm laser pump and could be used in high-energy laser systems, which makes Na 2 Ga 2 SiS 6 a promising candidate for high-energy IR NLO applications.