The interaction between cations and anionic groups inducing SHG enhancement in a series of apatite-like crystals: A first-principles study

•SHG response on a series of apatite-like borates was studied by a SHG-density method.•SHG responses are mainly attributed to BO3 groups and their alignment framework.•The contributions of A site are more important in CaBOF and CdBOF than in KSrBO.•Covalent interaction between BO and Cd is responsible for SHG of CdBOF.

It is an interesting topic to reveal the origin of the SHG intensity enhancement after substitution from alkali and alkali-earth metal atoms to cadmium in a series of apatite-like borates KSr4(BO3)3, Ca5(BO3)3F, Cd5(BO3)3F. Combined with the first-principles method, SHG-density method and real-space atom-cutting method, the electronic structure, the optical properties and the contribution of respective ion and ion groups have been investigated. Second harmonic generation (SHG) responses are mainly attributed to BO3 groups with π conjugated configuration and their alignment framework. The contributions of A site are more important in CaBOF and CdBOF compounds than in KSrBO. It is also demonstrated that the strong covalent interactions between the boron–oxygen groups and the cadmium atoms contribute the enhancement of SHG responses after substitution from alkali and alkali-earth metal atoms.

graphical abstractCombined with the first-principles method, SHG-density method and real-space atom-cutting method, the enhancement of SHG response are attributed to the interaction between cadmium and BO3 groups.Figure optionsDownload full-size imageDownload as PowerPoint slide