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 Ca 2 Na 3 (CO 3 ) 3 F was successfully synthesized through molecular engineering design, and large single crystals were grown by spontaneous crystallization with molten fluxes. The substitution of NLO-active [BO 3 ] groups for [CO 3 ] 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 Ca 2 Na 3 (CO 3 ) 3 F have been greatly improved. Remarkably, Ca 2 Na 3 (CO 3 ) 3 F exhibited a wide transparent region with a deep-UV absorption edge at 190 nm. These results demonstrated Ca 2 Na 3 (CO 3 ) 3 F is a promising NLO material in the UV or deep-UV region.