NaHSO 4 ·H 2 O: A Promising Deep-Ultraviolet Nonlinear-Optical Bisulfate with Large Birefringence and a Second-Harmonic-Generation Effect.

Searching on the functional building units with ultrawide band gaps, large hyperpolarizabilities, and strong anisotropies is the key to finding new deep-ultraviolet (DUV) nonlinear-optical (NLO) materials. In this study, the polar covalent tetrahedral unit [SO 3 (OH)] - is studied by theoretical calculation and its excellent DUV optical properties are revealed. Moreover, we thoroughly investigate the known bisulfates, finding a promising DUV NLO crystal, NaHSO 4 ·H 2 O. It exhibits a large second-harmonic-generation (SHG) response of 1.5 times that of KH 2 PO 4 and a short cutoff edge (shorter than 190 nm). Meanwhile, it has the largest birefringence of 0.042 at 546 nm among the DUV NLO sulfates. Our study suggests that bisulfates should be fresh and ideal DUV NLO candidates.