Strong Second- and Third-Harmonic Generation in 1D Chiral Hybrid Bismuth Halides

Area of Science:

• Materials Science
• Optics
• Solid-State Physics

Background:

• Breaking crystal symmetry enables nonlinear optical effects like second-harmonic generation (SHG). Chiral hybrid organic-inorganic metal halides are promising but lag behind traditional crystals due to limited research on resonant enhancement and third-harmonic generation (THG).
• Current nonlinear optical materials often lack the specific structural and electronic properties needed for efficient resonant enhancement of SHG and THG.

Purpose of the Study:

• To design and investigate chiral hybrid bismuth halides with 1D crystal structures for enhanced nonlinear optical properties.
• To explore the potential of these materials for efficient SHG and THG through resonant enhancement mechanisms.
• To compare the nonlinear performance of these novel materials with established nonlinear crystals.

Main Methods:

• Design and synthesis of chiral hybrid bismuth halides with inherent asymmetry and 1D crystal structures.
• Characterization of their optical and electronic properties, focusing on exciton behavior and band energy levels.
• Measurement and comparison of effective second-harmonic generation (SHG) and third-harmonic generation (THG) susceptibilities at 1550 nm.

Main Results:

• The synthesized chiral bismuth halides exhibit superior effective SHG susceptibility (χ(2) ∼ 130.5 pm V⁻¹) compared to commercial LiNbO₃ (χ(2) ∼ 83.4 pm V⁻¹).
• These materials demonstrate strong free excitons, broad self-trapped excitons (STE), and discrete energy levels, facilitating resonant enhancement.
• Remarkably, their THG intensities are higher than SHG intensities, with effective THG susceptibility (χ(3) ∼ 9.0 × 10⁶ pm² V⁻²) significantly outperforming reference materials like WS₂.

Conclusions:

• 1D chiral hybrid bismuth halides are highly promising for nonlinear optical applications due to their unique structural and electronic properties.
• The observed resonant enhancement of SHG and THG in these materials opens new avenues for developing high-performance nonlinear optical devices.
• These findings establish a new class of materials for efficient frequency conversion, surpassing current benchmarks.