Prospects for Fluoride Carbonate Nonlinear Optical Crystals in the UV and Deep-UV Regions

Combined with first-principles simulations and materials design considerations, the prospects of fluoride carbonate nonlinear optical (NLO) crystals in the ultraviolet (UV) and deep-UV regions are investigated. The A l (CO 3 ) k F m -type ( A represents the alkaline and/or alkaline-earth metal elements) carbonates are focused since they have exhibited the potential for the UV harmonic generation. The recently discovered MN CO 3 F ( M = K, Rb, Cs; N = Ca, Sr, Ba) series are selected as the representative examples to study the linear and nonlinear properties. It is revealed that MN CO 3 F possess very large birefringence and a strong NLO effect; thus, they are suitable to be good NLO and birefringent crystals in the UV region. Nevertheless, these carbonates cannot be applied in the deep-UV region because of their relatively small energy band gaps. To overcome this problem, we propose that the appropriate choice of the cations A would effectively enlarge the band gaps, which will greatly extend the applications of fluoride carbonates into the deep-UV region.