Nonlinear Optical Properties of 0D Chiral Hybrid Bismuth Iodides.
basic_science · Level V
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- Record sourced from PubMed, PMID 40178326.
- Also identified by DOI 10.1002/adma.202501022.
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Abstract
Chiral hybrid metal halides show great promise for nonlinear optical (NLO) applications like circularly polarized second harmonic generation (SHG). The inherent toxicity of lead is a concern for the widespread adoption of frequently explored lead-based chiral hybrid halides. Here, we report the second and third-order NLO properties of lead-free 0D chiral compounds, (R-/S-MBA)<sub>4</sub>Bi<sub>2</sub>I<sub>10</sub>, and their achiral counterpart, (Rac-MBA)<sub>4</sub>Bi<sub>2</sub>I<sub>10</sub> (MBA: methylbenzylammonium) under excitation wavelength ranging 1360-1590 nm. Chiral (R-/S-MBA)<sub>4</sub>Bi<sub>2</sub>I<sub>10</sub> exhibits strong SHG along with stronger third harmonic generation (THG). The chiral crystals showed high sensitivity to the handedness of circularly polarized pump light (g<sub>SHG - CD</sub> ≈ 9% at 1510 nm). The THG response shows resonance enhancement matching the excitonic absorption. Achiral (Rac-MBA)<sub>4</sub>Bi<sub>2</sub>I<sub>10</sub> exhibits the maximum THG response (χ<sup>(3)</sup> = 1.05 × 10⁻¹⁸ m<sup>2</sup> V<sup>-</sup> <sup>2</sup>)<sub>.</sub> Z-scan measurements with non-resonant femtosecond pulse excitation at 800 nm yield high nonlinear absorption coefficients (β) and nonlinear refractive index (n<sub>2</sub>) for all three samples, with (Rac-MBA)<sub>4</sub>Bi<sub>2</sub>I<sub>10</sub> exhibiting the highest values. These hybrid chiral metal halides, with efficient second and third-order nonlinearity, and high optical stability, are potential candidates for NLO applications such as Kerr-based optical switching, circularly polarized up-conversion, and communication.