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)4Bi2I10, and their achiral counterpart, (Rac-MBA)4Bi2I10 (MBA: methylbenzylammonium) under excitation wavelength ranging 1360–1590 nm. Chiral (R-/S-MBA)4Bi2I10 exhibits strong SHG along with stronger third harmonic generation (THG). The chiral crystals showed high sensitivity to the handedness of circularly polarized pump light (gSHG − CD ≈ 9% at 1510 nm). The THG response shows resonance enhancement matching the excitonic absorption. Achiral (Rac-MBA)4Bi2I10 exhibits the maximum THG response (χ(3) = 1.05 × 10⁻¹⁸ m2 V−2). Z-scan measurements with non-resonant femtosecond pulse excitation at 800 nm yield high nonlinear absorption coefficients (β) and nonlinear refractive index (n2) for all three samples, with (Rac-MBA)4Bi2I10 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.