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.