title: The mechanism for the nonlinear optical properties in La₉Na₃B₈O₂₇, La₂Na₃B₃O₉ and La₂CaB₁₀O₁₉: ab initio studies.
abstract: The nonlinear optical (NLO) properties in La9Na3B8O27, La2Na3B3O9 and La2CaB10O19 are investigated using a plane-wave pseudopotential method. Based on the first-principles electronic band structures, the birefringence and second harmonic generation (SHG) coefficients for the three crystals are determined. The calculated values match well with the experimental results. In order to elucidate the microscopic origins of the NLO performances in these crystals, a real-space atom-cutting method is adopted to calculate the contribution from the respective ions and groups. It is revealed that the La cations have covalent interactions with the neighbor O ions so as to form the La-O groups. The La-O bond covalency, combined with the distortion of La-O groups, makes the large contribution to the overall SHG coefficients in addition to the B-O groups, as also intuitively demonstrated by a SHG-density analysis.
authors.affiliation: Center for Crystal R&D, Key Lab of Functional Crystals and Laser Technology of Chinese Academy of Sciences, Technical Institute of Physics and Chemistry, CAS, Beijing 100190, People's Republic of China. University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
authors.forename: Jia
authors.initials: J
authors.lastname: Zhang
authors.forename: Lei
authors.initials: L
authors.lastname: Kang
authors.forename: Tse-Hsing
authors.initials: TH
authors.lastname: Lin
authors.forename: Xingxing
authors.initials: X
authors.lastname: Jiang
authors.forename: Pifu
authors.initials: P
authors.lastname: Gong
authors.forename: Ming-Hsien
authors.initials: MH
authors.lastname: Lee
authors.forename: Zheshuai
authors.initials: Z
authors.lastname: Lin