Lead Tellurite Crystals BaPbTe2O6 and PbVTeO5F with Large Nonlinear-/Linear-Optical Responses due to Active Lone Pairs and Distorted Octahedra

The exploration of nonlinear-/linear-optical crystal materials with high performance is an extremely difficult research project. Herein, the two new lead tellurite crystals BaPbTe2O6 and PbVTeO5F were successfully obtained through a facile hydrothermal synthesis strategy. BaPbTe2O6 lies in the noncentrosymmetric (NCS) and chiral orthorhombic space group P2(1)2(1)2(1), featuring a unique (1)(infinity)[PbTe2O6] chain consisting of the PbO4 and TeO3 building units, while PbVTeO5F belonging to the centrosymmetric (CS) orthorhombic space group Pbca manifests a 2D layer made up of (1)(infinity)[PbO4F2] chains and novel [V2Te2O10F2] clusters. Further, a systematic analysis of lead tellurites finds that the coordination geometries of the Pb atom exert a considerable influence on the connection modes of Pb-O and Te-O building units. BaPbTe2O6 shows a great second-harmonic-generation (SHG) effect of similar to 5x the benchmark KH2PO4 (KDP) and a large optical birefringence of 0.086 at 590 +/- 3 nm. PbVTeO5F demonstrates a remarkably larger birefringence of 0.142 at 590 +/- 3 nm, benefiting from the introduction of the VO5F octahedral unit. Theoretical studies reveal that the large SHG and birefringence in BaPbTe2O6 can be attributed to TeO3 and PbO4 polyhedra with active lone pairs, while the remarkably enlarged birefringence in PbVTeO5F is attributable to the highly distorted octahedral VO5F. The functional orientations of active building units may offer a practical insight into the design of the desired optical functional materials.