Synthesising a series of promising ultraviolet nonlinear optical materials with the aid of the flexibility of isolated [B5O10] groups

Abstract

Eight new compounds, namely K₇MgSc₂(B₅O₁₀)₃, K₇Sr_0.34Sc_2.44(B₅O₁₀)₃, K₆Li_0.94BaY_2.02(B₅O₁₀)₃, K₆NaBaY₂(B₅O₁₀)₃, Rb_5.3Na_3.7Y₂(B₅O₁₀)₃, Rb₆Na_1.5Y_2.5(B₅O₁₀)₃, K₆Na_1.82Y_2.18(B₅O₁₀)₃, and K₇Mg_0.88Zn_0.12Y₂(B₅O₁₀)₃, were successfully synthesized with the aid of the flexibility of isolated anion groups. All the compounds crystallize in the non-centrosymmetric (NCS) space group R32. Their structures feature a zero-dimensional configuration composed of isolated [B₅O₁₀] groups, which are connected by an [MO₆]-based octahedron, forming a three-dimensional framework with tunnels filled by the other cations. The compounds show an appropriate second harmonic generation (SHG) response, comparable to that of commercial KH₂PO₄ (KDP), and a short ultraviolet (UV) cut-off edge (<190 nm), achieving optimal balance between the two critical parameters for nonlinear optical (NLO) applications in the UV region. Additionally, for a deeper investigation of the structural flexibility, a comparison was carried out in A₇MRE₂(B₅O₁₀)₃ (A = alkali metal, M = divalent element, and RE = rare earth metal) structures. The fascinating results indicate that the single point link between the M cation-centered octahedron and isolated [B₅O₁₀] groups increases the structural flexibility and adjustability to accommodate varied cations, providing the foundations for the design of novel compositions.