Deep-ultraviolet nonlinear optical crystals: Ba3P3O10X (X = Cl, Br)

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Deep-ultraviolet nonlinear optical (NLO) crystals are crucial for generating coherent light below 200 nm via second-harmonic generation (SHG).
• Developing novel deep-UV NLO materials with short UV cutoff edges and efficient NLO properties remains a significant challenge.

Purpose of the Study:

• To discover and characterize new deep-ultraviolet NLO phosphate crystals.
• To investigate the structure-property relationships governing their NLO performance.

Main Methods:

• Synthesis and crystallographic analysis of novel phosphate compounds.
• Powder and single-crystal SHG measurements.
• Density Functional Theory (DFT) calculations for electronic structure and NLO property analysis.

Main Results:

• Discovery of unprecedented deep-UV NLO phosphates, Ba3P3O10Cl (BPOC) and Ba3P3O10Br (BPOB), representing new structure types.
• These materials exhibit moderate powder SHG intensities with type I phase-matching behavior.
• A short UV cutoff edge of approximately 180 nm was measured for single crystals, among the shortest for phosphates.
• DFT calculations revealed that the SHG response originates from the synergistic effects of asymmetric [P3O10](5-) anions, Ba(2+) cations, and halide anions (Cl-/Br-).

Conclusions:

• BPOC and BPOB are promising deep-UV NLO materials with excellent UV transparency and efficient SHG properties.
• The crystal packing significantly influences the geometry and polarization of the [P3O10](5-) building unit, impacting NLO performance.
• The combined contributions of anionic and cationic components are key to achieving efficient NLO responses in these novel phosphates.