A nitrate nonlinear optical crystal Pb16(OH)16(NO3)16 with a large second-harmonic generation response

Area of Science:

• Inorganic Chemistry
• Materials Science
• Solid State Physics

Background:

• Noncentrosymmetric materials are crucial for nonlinear optical (NLO) applications.
• Hydrothermal synthesis offers a versatile route for crystal growth.
• Lead-based compounds are known for their diverse structural and optical properties.

Purpose of the Study:

• To synthesize and characterize a novel noncentrosymmetric nitrate compound.
• To investigate the second-harmonic generation (SHG) properties of the synthesized material.
• To elucidate the structural origins of its NLO response.

Main Methods:

• Hydrothermal synthesis for crystal preparation.
• Powder second-harmonic generation (SHG) using the Kurtz-Perry technique.
• Bond-valence site energy (BVSE) calculations to quantify dipole moments.
• Density functional theory (DFT) for electronic structure calculations.

Main Results:

• Successful synthesis of Pb16(OH)16(NO3)16, a noncentrosymmetric nitrate.
• Demonstrated type I phase-matchable SHG with a coefficient 3.5 times that of KH2PO4.
• Quantified contributions of PbOn polyhedra and nitrate triangles to the large SHG response.
• Calculated electronic band structure, density of states, and electron density difference.

Conclusions:

• Pb16(OH)16(NO3)16 is a promising material for nonlinear optical applications due to its significant SHG.
• The cooperative effect between lead-oxygen polyhedra and nitrate groups is key to its strong NLO response.
• Theoretical calculations support the experimental findings and provide insights into the electronic origins of the NLO properties.