Commercially available nonlinear crystals that transmit light in the infrared region are used in optics and photonics but tend to be easily damaged by laser light. Chinese researchers report a new IR nonlinear optical material with a laser damage threshold significantly higher than that of commercially available materials (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja412405u). Jingui Qin of Wuhan University and coworkers synthesized the new material, Rb2CdBr2I2, by heating RbBr and CdI2 in water and slowly evaporating the solvent. They obtained a crystal structure, which shows that the [CdBr2I2]2− anions align themselves as distorted tetrahedrons with the iodine atoms on the same side of cadmium, resulting in a net polarization. The material transmits light over the wavelength range 0.37–14 μm, is thermally stable to 490 °C, and has a laser damage threshold of 190 MW per cm2. This threshold is six times that of AgGaS2, a commercially available IR nonlinear optical material. Rb2CdBr2I2 has a calculated band gap of 3.35 eV, which is wider than that of other IR nonlinear optical materials and which may explain the high threshold for laser damage.
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