Discovery of excellent ultraviolet nonlinear optical materials in chlorates and bromates with highly stereochemically active lone pairs

The discovery of short-wave ultraviolet (SWUV, lambda(PM) < 266 nm, PM = phase-matching) and deep ultraviolet (DUV, lambda(PM) < 200 nm) nonlinear optical (NLO) crystals is urgently required and full of challenges. Unlike the conventional strategy of using pi-conjugated groups (such as BO3) as core motifs for constructing UV NLO crystals, herein the long-neglected stereochemically active lone pair (SCALP) groups ClO3 and BrO3 are innovatively proposed to be good UV NLO functional motifs based on the group property prediction, and the NLO performance of chlorates and bromates has been investigated systematically for the first time by first-principles methods. Benefiting from the high polarizability of ClO3 and BrO3 and their favorable alignments, the halate crystals AClO(3) and ABrO(3) (A = NH4, K, Rb and Cs) exhibit high SHG coefficients comparable to that of classical beta-BaB2O4 (4.2-4.8 x KDP for AClO(3) and 6.1-7.1 x KDP for ABrO(3)). Meanwhile, their wide band gaps and large optical anisotropy lead to very short lambda(PM) deep into DUV and SWUV (185-195 nm for AClO(3) and 210-220 nm for ABrO(3)). Remarkably, ABrO(3) shows a rare full-wavelength phase-matching capability. Hence AClO(3) and ABrO(3) could be promising DUV and SWUV NLO candidates, respectively, and the UV NLO potential of ClO3 and BrO3 is further demonstrated by profound mechanism analysis. This work opens up a new avenue for the development of SWUV and even DUV NLO materials.