Carbon dots shift colors under UV light for encryption and sensing

Fluorescent materials usually emit a single consistent color, and they are typically made from dyes or metallic components. Researchers reporting in ACS Central Science have now created carbon dots that can fluoresce in a range of colors under UV light, depending on their concentration and the liquid they are in. The team incorporated the new carbon dots into plastic decorations and used them to create a data encryption system, an advance that points toward smart optical materials able to sense their surroundings and convey information.

The work began with a familiar limitation. LEDs, solar cells, and some data protection or anti-counterfeiting 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, with particular interest in applications 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. According to the study, the dots’ surfaces make them respond differently and emit various colors based on their concentration, acidity, and the presence of different liquids, giving a single material a palette of behaviors rather than one fixed emission.

To build the particles, 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. That variation in the synthesis recipe produced two related materials whose behavior could then be compared across a series of tests.

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, a reversible switching behavior that suggests the response is tied to the chemical state of the particle surfaces rather than to degradation of the material. The reversibility matters for any sensing or encryption application, where a material must return to a defined state after each readout.

The solvent experiments extended the range further. 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. In other words, the same carbon dots could be tuned across much of the visible spectrum simply by changing the environment around them, whether that meant the liquid medium or how densely the particles were packed into a solution.

The team then moved the dots out of solution and into solid materials. They 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. The demonstration shows that the responsive particles can survive incorporation into plastic-like formats, which is a practical requirement for decorative, wearable, or packaging uses.

Encryption was the second major demonstration. The researchers used the dots’ color changes to create a multidimensional encryption system, encoding information through unique light, liquid, and acidity conditions. Because a message is only revealed under the correct combination of UV illumination, liquid environment, and acidity, the system layers several independent keys into one material. Together, these findings demonstrate potential uses of the new carbon dots in data security and anti-counterfeiting technologies, where multi-condition readouts are harder to duplicate than single-color fluorescent inks.

“This offers a new approach to designing smart optical materials that can sense their surroundings and convey information,” says Lu, a corresponding author of the study. The quote frames the work as a design platform: rather than choosing between a red material or a green one, a designer can deploy one carbon dot whose emission reports on the pH, solvent, or concentration of its surroundings, and whose color states can carry encoded information.

Commercialization is already on the agenda. The researchers are “actively exploring opportunities to commercialize the CDs, particularly for information encryption,” says Lu. Next, they will evaluate long-term stability, large-scale manufacturing, and production cost — the standard hurdles that separate a laboratory demonstration from a product that can sit in a banknote, a label, or a sensor for years. The authors acknowledge funding from The National Natural Science Foundation of China, The Natural Science Foundation of Henan Province, and the Joint Fund of Science and Technology R&D Plan of Henan Province. The study, published in ACS Central Science under the title “High-Efficiency Multistimuli Responsive Carbon Dots with Near-100% Photoluminescence Quantum Yield for Anticounterfeiting Technologies,” appeared on 2 November 2026.

Subject of Research: Multistimuli-responsive carbon dots with tunable fluorescence for sensing and data encryption

Article Title: Carbon dots that fluoresce their way through the rainbow

Article References: Carbon dots that fluoresce their way through the rainbow. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: carbon dots, fluorescence, UV light, data encryption, anti-counterfeiting, environmental sensing, pH-responsive materials, polymers, photoluminescence, ACS Central Science, smart optical materials, quantum yield