A Deep-UV Nonlinear Optical Borosulfate with Incommensurate Modulations.

Despite borate-sulfates composed of isolated borate and sulfate groups have been discovered for more than one century, borosulfates of B-O-S bonding have not been synthesized until 2012 and their properties remain rarely explored. Here, we report a new borosulfate, namely LiRb4 [B(SO4 )4 ], which shows potential as a bran-new class of deep-UV nonlinear optical (NLO) material. Remarkably, according to the in situ single-crystal X-ray diffraction, LiRb4 [B(SO4 )4 ] undergoes successive first-order phase transitions with incommensurate structural modulations under room temperature and low temperature with (3 + 1)D superspace groups of X2(α0γ)0 and P21 (α0γ)0, respectively. The first-principle calculations and structural analyses reveal that NLO properties, phase transitions, and incommensurate modulations are closely related to the [B(SO4 )4 ]5- super-tetrahedral units with B-O-S bonding. We anticipate that the unprecedented coexistence of deep-UV transparency, NLO responses, and incommensurate structural modulations in one borosulfate will bring new possibilities to understand the underlying concepts of physics and chemistry in aperiodic materials.