Decentering the Symmetry via Docking B and F in the KBe2BO3F2-Family Structure

Deep-ultraviolet (DUV; <200 nm) nonlinear optical crystals arouse a great research interest in modern optical material science as they are key parts of solid-state lasers. Since KBe2BO3F2 (KBBF) still is the only crystal which can generate DUV coherent light practically, exploring other available structures in the DUV region by revising KBBF-family structure templates is necessary. In this paper, two KBBF-family structures are designed by adjusting the directions of BO3 groups or docking B and F atoms in known beta-Be2BO3F (BBF). The first BBF structure with a P6322 space group is designed by strictly aligning the BO3 groups of even layers and odd layers in beta-BBF. It is very interesting that docking B and F atoms forms novel B-F bonds, which destroy the inversion symmetry of the structure, making the centrosymmetric beta-BBF structure with the R3 convert to a noncentrosymmetric BBF structure having the R3c space group. This noncentrosymmetric BBF structure exhibits a DUV cutoff edge shorter than 150 nm and a second harmonic generation effect comparable to that of KH2PO4 (KDP; d36 = 0.39 pm/V), indicating its feasibility as a frequency-doubling crystal in the DUV region. Our conversion design provides an effective way for uncovering noncentrosymmetric structures in KBBF-family structures. c space group

Automated summary

In this study, two new structures within the KBBF family were designed, and one of them exhibited good second harmonic generation effect in the DUV region, suggesting its potential applications.