Rb₂Sb₂OCl₆ Birefringent Crystal

0.4–13.5 μm Wide Transparency

First alkali-metal antimony(III) oxyhalide with hemidirected coordination induced by oxygenation, achieving birefringence an order of magnitude higher than its holodirected prototype.

Li-Xin, Yang · Cheng, Xiyue · Hu, Chun · Li, Xuan · Zhou, Zhengyang · Deng, Shuiquan · Jiang-Gao, Mao · Kong, Fang

Angewandte Chemie - International Edition 2025

Specifications

Birefringence

{'zh': '0.191', 'en': '0.191'}

Transparency range

{'zh': '0.4-13.5', 'en': '0.4-13.5'} μm

Advantages

Birefringence boosted by an order of magnitude

Oxygen substitution transforms Sb coordination from holodirected SbCl6 to hemidirected SbOCl4, activating lone pair electrons and raising birefringence from 0.017 to 0.191 at 550 nm, an 11.2-fold increase.

Broad infrared transparency

The crystal transmits well from 0.4 to 13.5 μm, covering the long-wave infrared band, suitable for infrared optical applications.

Millimeter-size single crystals achievable

Crystals of 6×6×2 mm³ have been successfully grown, indicating potential for practical processing.

Applications

• IR Polarization Optics：Used for IR polarizing prisms or waveplates, leveraging high birefringence and wide transparency.
• IR Spectroscopy：Serves as polarizing element in IR spectrometers to enhance spectral resolution and signal-to-noise ratio.
• LWIR Optics：Enables polarization control in the LWIR band, e.g., polarimetric imaging and optical isolation.