RbMgCO₃F: A New Beryllium-Free Deep-Ultraviolet Nonlinear Optical Material

A new deep-ultraviolet nonlinear optical material, RbMgCO₃F, has been synthesized and characterized. The achiral nonpolar acentric material is second harmonic generation (SHG) active at both 1064 and 532 nm, with efficiencies of 160 × α-SiO₂ and 0.6 × β-BaB₂O₄, respectively, and exhibits a short UV cutoff, below 190 nm. RbMgCO₃F possesses a three-dimensional structure of corner-shared Mg(CO₃)₂F₂ polyhedra. Unlike other acentric carbonate fluorides, in this example, the inclusion of Mg²⁺ creates pentagonal channels where the Rb⁺ resides. Our electronic structure calculations reveal that the denticity of the carbonate linkage, monodentate or bidendate, to the divalent cation is a useful parameter for tuning the transparency window and achieving the sizable SHG response.