This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Fluorescent materials usually emit a single consistent color. They are typically made from dyes or metallic components.
In contrast, researchers reporting in ACS Central Science have created carbon dots that can fluoresce in a range of colors under UV light, depending on the concentration and the liquid they're in. The team incorporated the new carbon dots into plastic decorations and used them to create a data encryption system. LEDs, solar cells and some data protection or anticounterfeiting technologies rely on materials that absorb invisible UV light and then emit visible, colored light.
But their glow is usually a single distinct color—think of the bright blue of white clothing or teeth under a blacklight. Siyu Lu, Lin Ai and colleagues wanted to make more versatile fluorescent materials that shift between different colors in response to their surroundings. They were especially interested in these materials for environmental sensing and dynamic information encryption.
The researchers turned to carbon dots—tiny particles that can fluoresce brightly and whose surfaces are adjustable. By tuning those surfaces, they found that the same dot could fluoresce in different colors in varying conditions. First, the researchers heated two carbon-based compounds in an organic solvent under pressure, forming particles with carbon-rich cores and chemically responsive surfaces.
They made two versions, CD1 and CD2, using different ratios of the starting materials. In tests, CD1 fluoresced red in acidic water and green in alkaline water. Shifting the pH caused the color change to reverse repeatedly without changing the dots' brightness.
Similarly, when suspending CD1 and CD2 in different liquids—for example, water, toluene, methanol and ethanol—or varying the dots' concentration, the researchers observed that the dots changed their fluorescence, emitting colors from blue to red. Next, the researchers mixed carbon dot solutions with polymers to make blue, green, yellow and red materials. They incorporated carbon dot-polymer powders into crafts, including molded Chinese characters and decorative bottles, and folded flexible films into different shapes.
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