Adjustable optical nonlinearity in d cations containing chalcogenides via dp hybridization interaction.

The introduction of d10-metal cations is of importance in the design of infrared nonlinear optical materials. The role of d10-metal cations on the band gap and the second-harmonic generation (SHG) effect as well as the structure-property relationship were investigated in the Li2MGeS4 (M = Cd, Hg) and AB2S4 (A = Cd, Hg; B = Al, Ga) systems by using the first-principles calculations. The results show that the decreased band gap is related to a higher valence band maximum (VBM) caused by the larger dp repulsion from the Hg-5d orbitals and a downshift in the conduction band minimum (CBM) due to the lower energy of the Hg-6s orbitals. In addition, the relatively enhanced SHG response can be attributed to the decreased charge-transfer energy and the enhanced hybridization between the S-3p orbitals and the Hg-5d orbitals.