Hybrid Bismuth Halide with Rich Polymorphism and Second Harmonic Generation Response

Area of Science:

• Materials Science
• Solid-State Chemistry
• Optics

Background:

• Hybrid organic-inorganic materials offer combined properties but face challenges in nonlinear optics (NLO) due to limited understanding of noncentrosymmetric structure formation and characterization.
• Exploring new materials is crucial for advancing NLO applications.

Purpose of the Study:

• To investigate the formation, structural polymorphism, and optical properties of (Et3NH)3Bi2Br9.
• To understand how the alignment of [Bi2Br9]3- units affects material symmetry and NLO behavior.
• To evaluate the potential of this material for NLO applications and as ionic liquids.

Main Methods:

• Crystallization and structural analysis to identify different polymorphs (centrosymmetric and noncentrosymmetric).
• Second harmonic generation (SHG) measurements to quantify NLO properties.
• Thermal analysis to study phase transitions and melting points.

Main Results:

• The (Et3NH)3Bi2Br9 composition was found to crystallize in both noncentrosymmetric and centrosymmetric forms.
• The alignment of [Bi2Br9]3- units was identified as the key factor determining phase symmetry and NLO properties.
• The triclinic polymorph demonstrated significant second harmonic generation (SHG) response (1.29 × KDP and 0.08 × AGS).
• Polymorphic phase transitions and low melting points were observed, indicating melt-processability.

Conclusions:

• Structural control over [Bi2Br9]3- unit alignment is critical for achieving noncentrosymmetric structures and desirable NLO properties.
• (Et3NH)3Bi2Br9 exhibits promising NLO characteristics and potential as a melt-processable material and ionic liquid candidate.
• Further research into hybrid materials can unlock new possibilities in nonlinear optics.