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

Graphical Laser damage limitation : Promising ternary infrared nonlinear optical (NLO) materials, Na 6 MQ 4 (M=Zn, Cd; Q=S, Se), with unique [NaQ 4 ] NLO-active groups, are successfully prepared. Theoretical calculations and statistical analyses indicate that the second-harmonic generation effect and band gap in the compounds originate mainly from the distorted NaQ 4 NLO-active units with a short Na−S bond length. 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, Na 6 MSe 4 (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5×AgGaS 2 ) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS 2 ). The two sulfides, Na 6 MS 4 (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS 2 ), but smaller SHG responses (0.3 and 0.2×AgGaS 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.