Rare-Earth Scandium Borate Fluoride with a Deep-Ultraviolet Cutoff Edge

Through reasonable selections of raw materials and experimental methods, a new rare-earth borate fluoride K₁₁Sc₅(B₅O₁₀)₄F₆ is synthesized successfully by the high-temperature solution method in a closed system, which is the first noncentrosymmetric scandium borate fluoride. It crystallizes in the Fdd2 space group of the orthorhombic crystal system and features an extremely complicated structure constructed by the fundamental building blocks [B₅O₁₀] units, Sc-based, and K-based polyhedra. To our knowledge, K₁₁Sc₅(B₅O₁₀)₄F₆ is the only rare-earth borate that contains two kinds of [B₅O₁₀] groups and crystallizes in the Fdd2 space group, enriching the structural chemistry of rare-earth borates and rare-earth borate fluorides. Additionally, it is discussed in detail how F can significantly improve performance by modifying the modules in a comparison of structures. Discussion on rational synthetic conditions is instructive for obtaining rare-earth borate fluorides. Furthermore, a short cutoff edge (<190 nm) is experimentally confirmed, indicating the potential application of K₁₁Sc₅(B₅O₁₀)₄F₆ in ultraviolet/deep-ultraviolet regions.