The mechanism for the nonlinear optical properties in La₉Na₃B₈O₂₇, La₂Na₃B₃O₉and La₂CaB₁₀O₁₉:ab initiostudies

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.

Pushing Nonlinear Optical Oxides into the Mid-Infrared Spectral Region Beyond 10 μm: Design, Synthesis, and Characterization of La3SnGa5O14

“…This indicates that rare-earth cations and their neighboring ions (i.e., O 2– anions) must be considered as a whole group, which can provide a large contribution to the overall SHG effect in langasites. This conclusion was also confirmed in other NLO materials containing rare-earth cations, such as Na 3 La 9 B 8 O 27 , Na 3 La 2 B 3 O 9 , and La 2 CaB 10 O 19 . Second, (ii) the GaO 6 octahedra at the [ B O 6 ] sites provides a small contribution to the overall SHG coefficient, as short Ga–O bonds are not favorable for large induced dipole moments for NLO generation.…”

LaSiP3 and LaSi2P6: Two Excellent Rare‐Earth Pnictides with Strong SHG Responses as Mid‐ and Far‐Infrared Nonlinear Optical Crystals

“…First, introducing rare‐earth metals with strong ionicity can effectively widen the band gap, thus enhancing the LDT. [ 9 ] Secondly, rare‐earth metals have high coordination number, often forming irregular polyhedral structure units, which is beneficial to improve SHG responses. [ 10 ] Thirdly, rare‐earth compounds have good thermal stability and favorable transmittance in the IR regions.…”

Chromium iodate: the structure and origin of optical second harmonic generation

“…Mulliken bond population analysis clearly suggests that there should be a strong covalent interaction between Cr and neighboring O atoms in CIO (Table S6†). In recent years, there has been increasing interest in examples of metal cationic center units contributing significant NLO effects, 23,26 with most of these cations being transition metals and rare earth ions. This study provides an example of a transition metal iodate.…”