Molecular Engineering as an Approach To Design a New Beryllium-Free Fluoride Carbonate as a Deep-Ultraviolet Nonlinear Optical Material

It is a great challenge to explore deep-ultraviolet (deep-UV) nonlinear optical (NLO) materials that can achieve a subtle balance among large nonlinear coefficients, moderate birefringence, and deep-ultraviolet (UV) transparency. A new beryllium-free fluoride carbonate Ca₂Na₃(CO₃)₃F was successfully synthesized through molecular engineering design, and large single crystals were grown by spontaneous crystallization with molten fluxes. The substitution of NLO-active [BO₃] groups for [CO₃] groups resulted in an optimal balance among the SHG coefficient, birefringence, and UV transparency. Via comparison of these two iso-structural compounds, the second-harmonic generation coefficients and birefringence of Ca₂Na₃(CO₃)₃F have been greatly improved. Remarkably, Ca₂Na₃(CO₃)₃F exhibited a wide transparent region with a deep-UV absorption edge at 190 nm. These results demonstrated Ca₂Na₃(CO₃)₃F is a promising NLO material in the UV or deep-UV region