Lead Tellurite Crystals BaPbTe 2 O 6 and PbVTeO 5 F 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 BaPbTe 2 O 6 and PbVTeO 5 F were successfully obtained through a facile hydrothermal synthesis strategy. BaPbTe 2 O 6 lies in the noncentrosymmetric (NCS) and chiral orthorhombic space group P 2 1 2 1 2 1 , featuring a unique ∞ 1 [PbTe 2 O 6 ] chain consisting of the PbO 4 and TeO 3 building units, while PbVTeO 5 F belonging to the centrosymmetric (CS) orthorhombic space group Pbca manifests a 2D layer made up of ∞ 1 [PbO 4 F 2 ] chains and novel [V 2 Te 2 O 10 F 2 ] 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. BaPbTe 2 O 6 shows a great second-harmonic-generation (SHG) effect of ∼5× the benchmark KH 2 PO 4 (KDP) and a large optical birefringence of 0.086 at 590 ± 3 nm. PbVTeO 5 F demonstrates a remarkably larger birefringence of 0.142 at 590 ± 3 nm, benefiting from the introduction of the VO 5 F octahedral unit. Theoretical studies reveal that the large SHG and birefringence in BaPbTe 2 O 6 can be attributed to TeO 3 and PbO 4 polyhedra with active lone pairs, while the remarkably enlarged birefringence in PbVTeO 5 F is attributable to the highly distorted octahedral VO 5 F. The functional orientations of active building units may offer a practical insight into the design of the desired optical functional materials.