HgSO4: An excellent mid-infrared sulfate nonlinear optical crystal with wide band gap and strong second harmonic generation response

A mercury-based sulfate nonlinear optical (NLO) material, HgSO4, was successfully grown using a hydrothermal method. It crystallizes in the polar space group Pmn21 and forms a three-dimensional spatial network structure consisting of [HgO8] polyhedras and [SO4] polyhedras. The powder second harmonic generation (SHG) measurement showed that HgSO4 is a phase-matching material and has a very strong SHG efficiency of 11 times that of KDP. Such a remarkable SHG response is due to the well-ordered arrangement of the distorted [HgO8] and [SO4] polyhedras. In parallel, large bandgap (4.13 eV) and laser damage threshold (26.5 × AgGaS2) are exhibited. Further characterizations showed that this compound possesses a large birefringence and a wide transmission window from the near-UV to mid-IR, suggesting that HgSO4 may be an excellent mid-IR NLO crystal.