K2S4O6: improving birefringence and nonlinear optical properties with the [O3S–S–S–SO3]2− group

Compared with sulfate SO 4 2− group, tetrathionate [O 3 S–S–S–SO 3 ] 2− group could improve birefringence and second-harmonic generation effects as K 2 S 4 O 6 demonstrates.