Chemical Cosubstitution-Oriented Design of Rare-Earth Borates as Potential Ultraviolet Nonlinear Optical Materials

A chemical cosubstitution strategy was implemented to design potential ultraviolet (UV) and deep-UV nonlinear optical (NLO) materials. Taking the classic β-BaB 2 O 4 as a maternal structure, by simultaneously replacing the Ba 2+ and [B 3 O 6 ] 3– units with monovalant (K + ), divalent (alkaline earth metal), trivalent (rare-earth metal, Bi 3+ ) ions, and the [B 5 O 10 ] 5– clusters through two different practical routes, 12 new mixed-metal noncentrosymmetric borates K 7 M II RE 2 (B 5 O 10 ) 3 (M II = Ca, Sr, Ba, K/RE 0.5; RE = Y, Lu, Gd) as well as K 7 M II Bi 2 (B 5 O 10 ) 3 (M II = Pb, Sr) were successfully designed and synthesized as high-quality single crystals. The selected K 7 CaY 2 (B 5 O 10 ) 3, K 7 SrY 2 (B 5 O 10 ) 3, and K 7 BaY 2 (B 5 O 10 ) 3 compounds were subjected to experimental and theoretical characterizations. They all exhibit suitable second-harmonic generation (SHG) responses, as large as that of commercial KH 2 PO 4 (KDP), and also exhibit short UV cutoff edges. These results confirm the feasibility of this chemical cosubstitution strategy to design NLO materials and that the three selected crystals may have potential application as UV NLO materials.