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Chemistry In Pictures

Chemistry in Pictures: All hail halides

by Alexandra Taylor
March 27, 2019

A photo of four fluorescing flasks with pipettes in them.
Credit: Lea Nienhaus

These flasks all contain CsPbBr3 nanocrystals excited with an ultraviolet lamp. The size of the crystals dictates what color they glow when excited. The second flask from the left contains small particles, while the third from the left contains large particles, making it a bright green. The flasks on the ends both contain the same material as the bright green flask, but they’ve been mixed with lithium chloride (left) and lithium iodide (right) to turn the contents blue and orange, respectively. Florida State University chemistry professor Lea Nienhaus and her group tuned the emission colors of the perovskite nanocrystals through a process called halide exchange. “Halide ions are highly mobile in perovskites, so we can replace them by simply adding an excess of a new halide into the flask, and the color will rapidly change,” Nienhaus explains. She set pipettes containing the CsPbBr3 starting material into the flasks after adding the halides. The ions slowly diffused up the pipette capillary, creating the deep blue to light blue and orange to green transitions shown. Nienhaus’s group aims to better understand the fundamental properties of perovskites for applications in solar energy harvesting, lighting, and energy conversion.

Submitted by Lea Nienhaus

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