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 K 11 Sc 5 (B 5 O 10 ) 4 F 6 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 Fdd 2 space group of the orthorhombic crystal system and features an extremely complicated structure constructed by the fundamental building blocks [B 5 O 10 ] units, Sc-based, and K-based polyhedra. To our knowledge, K 11 Sc 5 (B 5 O 10 ) 4 F 6 is the only rare-earth borate that contains two kinds of [B 5 O 10 ] groups and crystallizes in the Fdd 2 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 K 11 Sc 5 (B 5 O 10 ) 4 F 6 in ultraviolet/deep-ultraviolet regions.