Cs2 Bi2 O(Ge2 O7 ) (CBGO): A Larger SHG Effect Induced by Synergistic Polarizations of BiO5 Polyhedra and GeO4 Tetrahedra.

A cesium bismuth germanate, Cs2 Bi2 O(Ge2 O7 ) (CBGO), was synthesized by a traditional high-temperature solid-state reaction. Its structure features a 3D network composed of a 1D chains composed of Bi2 O8 dimers that are further bridged by Ge2 O7 dimers, forming tunnels of seven member rings (MRs) that are filled by the Cs+ cations. CBGO exhibits extraordinary larger second harmonic generation (SHG) response of about 13.7 times that of KDP (KH2 PO4 ) under 1064 nm laser radiation and 1.1 times that of KTP (KTiOPO4 ) under 2.05 μm laser radiation, which is the highest among all of the metal germanates reported so far. CBGO possesses a moderate birefringence (0.073 at 1064 nm) and is phase matchable. Furthermore, CBGO melts congruently and exhibits high thermal stability.