Ultrawide Bandgap and Record-High Birefringence in a Covalent Beryllium-Organic Framework

Area of Science:

• Materials Science
• Crystallography
• Optics

Background:

• Designing optical crystals faces a trade-off between wide bandgap and large birefringence.
• Anisotropic structural motifs often lead to narrow energy gaps, limiting performance.

Purpose of the Study:

• To overcome the bandgap-birefringence trade-off in optical crystals.
• To develop a quantitative screening strategy for functional groups in short-wave ultraviolet (UV)-transparent crystals.

Main Methods:

• Integrated 1,3,5-benzenetricarboxylate octupolar motifs with tetrahedral Be2+ cations.
• Synthesized a covalent beryllium-organic framework crystal (I).
• Analyzed electronic structure and optical properties.

Main Results:

• Crystal I exhibits an ultrawide bandgap (5.00 eV) and a short-wave UV cutoff (248 nm).
• Achieved a record-high birefringence (0.60) in the short-wave UV region.
• Demonstrated exceptional optical quality factor (Q = 3.00).

Conclusions:

• The novel crystal structure breaks the intrinsic performance bottleneck for birefringent materials.
• Establishes a viable platform for ultrawide bandgap birefringent crystals.
• Enables next-generation photonic applications requiring high performance in the UV spectrum.