Role of the metal cation types around VO4 groups on the nonlinear optical behavior of materials: experimental and theoretical analysis

Abstract

In order to explore new NLO crystals with superior performances, it is greatly desirable to understand the intrinsic relationship between the macroscopic optical properties and microscopic structural features in crystals. A novel mechanism for nonlinear optical (NLO) effects of vanadate crystals, Li₃VO₄, KCd₄(VO₄)₃ and Ca₃(VO₄)₂ with distorted (VO₄)³⁻ groups, has been investigated. Experiments related to the synthesis and structures were determined. In addition, infrared and UV-Vis-NIR diffuse reflectance spectroscopy, as well as electronic band structure calculations, were performed on the reported materials. A comprehensive analysis for the structure–property relationship is given by combining the experimental measurements, the electronic structure calculations and the SHG-weighted electron density to the linear and NLO properties. It was found that the contribution of the (VO₄)³⁻ anionic group to the second harmonic generation (SHG) response was the dominant anionic group, which plays a vital role to the SHG effects in Li₃VO₄, KCd₄(VO₄)₃ and Ca₃(VO₄)₂. It was also concluded that the metal cation types and coordination around VO₄ groups, the distorted and parallel oriented VO₄ tetrahedron decided the SHG coefficient values.