Lone electron-pair enhancement of SHG responses in eulytite-type compounds: A(II)(3)M(III)(PO(4))(3) (A = Pb, M = Bi; A = Ba, M = Bi, La).

A new eulytite-like orthophosphate Pb(3)Bi(PO(4))(3), was synthesized by the high temperature solution growth (HTSG) method and characterized by X-ray single crystal diffraction, powder diffraction and electron microscopy. It crystallizes in the acentric cubic space group (I4[combining macron]3d). The pure-phase powders of Pb(3)Bi(PO(4))(3), Ba(3)La(PO(4))(3) and Ba(3)Bi(PO(4))(3) were also prepared by the high temperature solid reaction method. Second harmonic generation (SHG) measurements revealed that the optical response signals of Pb(3)Bi(PO(4))(3) and Ba(3)Bi(PO(4))(3) are about 3.0 and 0.5 times that of KH(2)PO(4) (KDP), respectively, and both are phase-matchable. The SHG signal of Ba(3)La(PO(4))(3) is very weak. Our studies indicate that the enhancement of the nonlinear optical response is mainly due to the contribution from the irregular PbO(6) and BiO(6) octahedra due to the 6s(2) lone electron-pair stereochemical activity in eulytite-like orthophosphates. Additionally, the calculated band structure and density of states also provide evidence that the charge transfers within irregular octahedral of Pb/BiO(6) make a significant contribution to the nonlinear optical response.