K6NaCaRe2(B5O10)3 (Re = Y, Lu): Two NLO Compounds Exhibiting a Short Absorption Edge in the A7–xA’xAeRe2(B5O10)3 (x = 0, 1) Family

Abstract

The discovery and synthesis of new NLO materials in the ultraviolet (UV) region are crucial to developing laser technology. The chemical substitution strategy is an effective pathway to design potential UV or DUV NLO crystals. Herein, two new compounds, K₆NaCaY₂(B₅O₁₀)₃ and K₆NaCaLu₂(B₅O₁₀)₃, have been synthesized using KB₅O₈·4H₂O as the template. Their crystal structures feature a three-dimensional (3D) [Re₂(B₅O₁₀)₃]_∞ framework consisting of [B₅O₁₀] groups and [ReO₆] octahedra, and the remainder of metal cations fill the void to control charge balance and maintain the stability of the crystal structure. Both K₆NaCaY₂(B₅O₁₀)₃ and K₆NaCaLu₂(B₅O₁₀)₃ crystallize in the acentric space group R32, so they exhibit an SHG effect, and the value is ∼0.5 × KDP (KH₂PO₄). Meanwhile, they show a phase-matching ability. Due to the participation of alkali metals, alkaline earth metal, and [B₅O₁₀] unit, the title compounds possess short absorption edges of ∼230 nm. In addition, they have high thermal stability and can be stable up to 931 °C. These results confirm the effectiveness of the chemical substitution strategy for designing NLO compounds, and then the two compounds can potentially serve as good UV NLO materials.