Three Borates Belonging to the A(I)7Ae(II)Re(III)2B15O30 Family as Promising Nonlinear Optical Crystals

Three borate crystals, namely, Rb7CaY2B15O30, NaRb6CaY2B15O30, and LiRb6CaY2B15O30, belonging to the A­(I)7Ae­(II)­Re­(III)2B15O30 family, were synthesized by the high-temperature solution method under open systems. The space groups of Rb7CaY2B15O30 and NaRb6CaY2B15O30 are both R32, while the space group of LiRb6CaY2B15O30 is C2221. The anion frames are all zero-dimensional clusters composed of isolated [B5O10] units. Mixed metallic elements with three distinct valence states fill the gaps between anion groups to balance charge and form overall three-dimensional structures. The ultraviolet cutoff edges are lower than 195, 185, and 200 nm for Rb7CaY2B15O30, NaRb6CaY2B15O30, and LiRb6CaY2B15O30, respectively. The second-harmonic generation response of Rb7CaY2B15O30 and NaRb6CaY2B15O30 is 1.4 and 1.2 × KDP, which makes them promising candidates for nonlinear optical crystals. A detailed discussion of the correlation between the structure and optical properties is presented through first-principles calculations.