Defective [Bi2O2]2+ Layers Exhibiting Ultrabroad Near-Infrared Luminescence

Aurivillius phases have been routinely known as excellent ferroelectrics and have rarely been deemed as materials that luminesce in the near-infrared (NIR) region. Herein, it is shown that the Aurivillius phases can demonstrate broadband NIR luminescence that covers telecommunication and biological optical windows. Experimental characterization of the model system Bi2.14Sr0.75Ta2O9-x, combined with theoretical calculations, help to establish that the NIR luminescence originates from defective [Bi2O2](2+) layers. Importantly, the generality of this finding is validated based on observations of a rich bank of NIR luminescence characteristics in other Aurivillius phases. This work highlights that incorporating defects into infinitely repeating [Bi2O2](2+) layers can be used as a powerful tool to space-selectively impart unusual luminescence emitters to Aurivillius-phase ferroelectrics, which not only offers an optical probe for the examination of defect states in ferroelectrics, but also provides possibilities for coupling of the ferroelectric property with NIR luminescence.