Na+/Ag+ substitution induced birefringence enhancement from AgGaS2 to NaGaS2

Birefringent materials are of great important as opto-electronic functional devices in solid laser system. Investigations on the design of new birefringent materials with large birefringence is meaningful. In this study, structure-birefringence relationship between AgGaS2 (AGS) and NaGaS2 (NGS) was systematically investigated. In the structures, the high ionic Na+ cations broke the three dimensional (3D) [GaS] network to 2D layers, which results in the regular packing of GaS4 tetrahedra and further the birefringence (~0.09, nearly twice that of AGS at ~1064 nm). Meanwhile, the blue-shift of the UV cutoff edge to 307 nm and a wide band gap of 3.9 eV has been observed in NGS. The property characterizations were carried out using the as-grown NGS single crystal with a size of 4 × 4 × 0.3 mm3 by high temperature flux method. The results indicate that NGS may be a promising IR birefringent material and the cation substitution-oriented design strategy could be used to regulate the structure and optical properties of materials.