Persistent Second-Harmonic Generation Enhancement Across an Unprecedented Pressure Range in a Hybrid Antimony Halide

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nonlinear Optics

Background:

• Organic-inorganic hybrid solids offer tunable optical properties.
• Stereochemically active lone-pair electrons (LPEs) typically correlate with structural distortion and second-harmonic generation (SHG) response.
• Pressure usually suppresses LPEs activity, limiting SHG enhancement in most halide systems.

Purpose of the Study:

• To investigate a novel zero-dimensional hybrid halide, (TMP)2(SbBr5)(SbBr3), for its nonlinear optical properties under pressure.
• To understand the mechanism behind sustained SHG enhancement in this material.
• To explore the role of structural transitions and electronic hybridization in modulating SHG response.

Main Methods:

• Synthesis and characterization of the (TMP)2(SbBr5)(SbBr3) hybrid halide.
• High-pressure X-ray diffraction and optical spectroscopy.
• Density Functional Theory (DFT) calculations for structural and electronic analysis.

Main Results:

• The material exhibits a continuous 2.1-fold SHG enhancement over a wide pressure range (0-8.88 GPa).
• This enhancement persists through an isostructural phase transition from 0D to 1D structures around 3.5 GPa.
• New Sb-S bonds and 1D chain formation enhance Sb-Br and Sb-S orbital hybridization and electron delocalization.

Conclusions:

• The observed sustained SHG enhancement is driven by changes in connectivity and enhanced orbital hybridization, not solely by LPEs activity.
• This finding provides a new paradigm for designing materials with continuously tunable nonlinear optical properties under external stimuli.
• The study highlights the importance of structural and electronic factors in optimizing nonlinear optical responses in hybrid materials.