Centric Sc(HPO3)(H2PO3)(H2O) and Acentric Sc(H2PO3)3: Two Ultraviolet Scandium Phosphite Optical Crystals

Exploring ultraviolet (UV) nonlinear-optical (NLO) materials is significant for the conversion of a high-frequency laser. Two scandium phosphites, Sc(HPO₃)(H₂PO₃)(H₂O) and Sc(H₂PO₃)₃, were successfully synthesized. Centric Sc(HPO₃)(H₂PO₃)(H₂O) exhibits a short UV cutoff edge (<200 nm) and a unique double-layer structure of [Sc₂(HPO₃)₂(H₂PO₃)₂(H₂O)₂]_∞. The acentric Sc(H₂PO₃)₃ exhibits a three-dimensional [Sc(H₂PO₃)₃]_∞ structure with a large band gap of 4.05 eV, and it demonstrates a moderately phase-matchable second-harmonic-generation response [0.60 × KDP (KH₂PO₄)] at 1064 nm. The crystal structures, optical properties, and theoretical calculations of the two compounds are discussed. This work will promote the exploration of new NLO phosphite materials.