K₆ACaSc₂(B₅O₁₀)₃ (A = Li, Na, Li_0.7Na_0.3): Nonlinear-Optical Materials with Short UV Cutoff Edges

Three new acentric Sc-based borates, K₆ACaSc₂(B₅O₁₀)₃ (A = Li, Na, Li_0.7Na_0.3; space group R32), have been obtained and characterized. They are isostructural, and all exhibit three-dimensional [Sc₂(B₅O₁₀)₃]^9- anionic architecture composed of B₅O₁₀ clusters and ScO₆ octahedra with the alkali- and alkaline-earth-metal cations occupying the cavities and keeping the charge balance. These compounds possess moderate second-harmonic-generation (SHG) responses (∼0.2×β-BaB₂O₄ at 532 nm and ∼0.4×KH₂PO₄ at 1064 nm) with phase-matching abilities and importantly display short cutoff edges below 200 nm. Furthermore, the relationship between the crystal structure and the SHG property has also been discussed based on the theoretical calculations.