Pb2TiOF(SeO3)2Cl and Pb2NbO2(SeO3)2Cl: small changes in structure induced a very large SHG enhancement

The replacement of NbO6 octahedra in Pb2NbO2(SeO3)(2)Cl by the TiO5F octahedra in Pb2TiOF(SeO3)(2)Cl induced a very large SHG enhancement from 2.3 x to 9.6 x KDP (KH2PO4), and both materials are type-I phase matchable. Theoretical calculations based on DFT methods indicate that the inclusion of F- anions in the d(0)-TM octahedral coordination unit has a great impact on the band structure and the SHG enhancement of the material.