Two non-centrosymmetric mixed alkali metal and alkaline earth metal scandium borate nonlinear optical materials with short ultraviolet cutoff edges

Abstract

Rare earth borates, a subset of the essential nonlinear optical (NLO) materials, have sparked a significant amount of attention in recent years. In self-fluxing systems, two non-centrosymmetric scandium borates with classical B₅O₁₀ groups, namely Rb₇SrSc₂B₁₅O₃₀ (I) and Rb₇CaSc₂B₁₅O₃₀ (II), were successfully discovered. Both I and II exhibit a short ultraviolet (UV) cutoff edge (<200 nm) and appropriate second-harmonic generation efficiency (∼0.76 × KH₂PO₄, ∼0.88 × KH₂PO₄ at 1064 nm, respectively). According to theoretical calculations, it is speculated that the band gap and NLO characteristics of these two compounds are mostly derived from the B₅O₁₀ group and the ScO₆ octahedron. Due to the short cutoff edges of I and II, they may be considered as potential NLO materials in the UV and even deep UV spectral ranges. Furthermore, the advent of I and II adds to the diversity of rare earth borates.