Trithionic guanidine: A novel semi-organic short-wave ultraviolet nonlinear optical sulfate with dimeric heteroleptic tetrahedra

Sulfates are always promising short-wave ultraviolet (UV) nonlinear optical (NLO) candidates, if their birefringence could be greatly improved. Here, in terms of the insufficient birefringence , the unity of heteroleptic tetrahedral groups and triangular ones was proposed and implemented. Thus, a new semi-organic crystal, [C(NH 2 ) 3 ]S 3 O 6 (G 2 S 3 O 6 ), was obtained, which is composed of [S 3 O 6 ] 2− and [C(NH 2 ) 3 ] + groups. It exhibits excellent optical properties with a short absorption cutoff edge of 218 nm, a strong NLO response of 1.4 × KH 2 PO 4 , and more especially, a large birefringence of 0.097@546 nm. This birefringence leap makes the G 2 S 3 O 6 crystal achieve a phase-matching behavior under a 532 nm laser. Thus, the synergy of [S 3 O 6 ] 2− and [C(NH 2 ) 3 ] + groups results in excellent optical performances. This finding opens a new horizon for exploring novel UV NLO crystals.