Zn(C 2 H 4 NO 2 ) 2 (SO 2 CH 3 NH 2 ) 2 and Zn(C 2 H 4 NO 2 ) 2 [SO 2 (NH 2 ) 2 ]: Regulation of Unique ZnO(C 2 H 4 NO 2 ) 2 Units by Polar Tetrahedrons for Balanced UV Nonlinear Optical Performance

, and a large birefringence of 0.126@546 nm. Remarkably, its phase-matching range covers the entire transparent wavelength range, namely, the shortest phase-matching wavelength is 209 nm. This work provides a potential short-wave UV NLO crystal and offers new insights for the design of such crystals.