Inorganic metal halides play important roles in wide range of areas including fluorescence, X-ray detection, and nonlinear-optics. Herein, two new mixed alkali metal tantalum fluorides, CsKTaF7 and CsNaTaF7 , have been obtained based on the strategy of cations regulation in A2 MF7 (A represents monovalent cations and M is d0 transition-metal cation) system by a conventional hydrothermal route. CsKTaF7 crystallizes in the centric Pnma space group, while CsNaTaF7 crystallizes in the polar Cmc21 space group and exhibits moderate and phase-matchable NLO activity. Both halides possess large optical band gaps above 5.0 eV. The crystal structure evolution, optical properties, and detailed theory calculations of these two halides were elucidated in this work.
Keywords: alkali metal cations; crystal structures; d0 transition-metal fluorides; noncentrosymmetric structure; second-order nonlinear optical.
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