A promising lead-free fluoride carbonate SHG material designed from a theoretical perspective

In recent years, a series of fluoride carbonate crystals, as second harmonic generation (SHG) materials, have been considerably developed; however the lead in these materials is a potential threat to the environment. In this study, the structure, mechanical and optical properties of ABCO3F (A = Rb, Cs; B = Ge, Sn) were systematically investigated to find alternatives to APbCO3F. We found that the RbSnCO3F crystal displays substantial stability and remarkable linear optical properties compared with those of the lead fluoride carbonate SHG materials. In particular, RbSnCO3F exhibits unexpected anisotropy of refractive indices, a key feature to satisfy the phase matching condition in the ultraviolet spectral region. In addition, RbSnCO3F shows a large SHG response, about 21 times that of KH2PO4 (KDP) with the coefficient of 8.21 pm V−1. Our results highlight that RbSnCO3F should be a candidate for a lead-free fluoride carbonate SHG material for achieving coherent light output in laser fields. This investigation also unravels the structure–property relationship of fluoride carbonates, contributing to explore more excellent SHG materials in future.