Na6MQ4 (M=Zn, Cd; Q=S, Se): Promising New Ternary Infrared Nonlinear Optical Materials

Four sodium-based ternary IR nonlinear optical (NLO) materials, Na(6)MQ(4) (M=Zn, Cd; Q=S, Se), were prepared through a high-temperature flux method. The crystal structure of the compounds is built up of isolated [MQ(4)] tetrahedra and a 3D framework formed by the NaQ(n) (n=4, 5) units. The two selenides, Na6MSe4 (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5xAgGaS(2)) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9xAgGaS(2)). The two sulfides, Na6MS4 (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4xAgGaS(2)), but smaller SHG responses (0.3 and 0.2xAgGaS(2)). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ(4) NLO-active units with a short Na-S bond length, which provides a new insight into the design of novel IR NLO materials.

Automated summary

Four newly synthesized sodium-based ternary IR nonlinear optical materials exhibit different second-harmonic generation responses and laser damage thresholds, with selenides showing better SHG responses and sulfides having higher laser damage thresholds. The SHG effect and band gap in these compounds mainly originate from the distorted NaQ(4) NLO-active units with a short Na-S bond length, providing new insights for the design of novel IR NLO materials.