Carbon black butterfly brought to light

NUS researchers have shown that carbon black, a common pigment, demonstrates a range of beautiful colours when heated with a focussed laser, and has the potential to be used in fluorescence displays.

Recovered carbon black powder is a common pigment produced from burnt rubber tyres. Just like focusing the sun to burn paper, focusing a laser beam can further burn the recovered carbon black. Yet instead of turning the material into ash, researchers from NUS Physics and the Centre for Advanced 2D Materials have shown that it can be transformed into a dazzling multi-coloured fluorescence and visual display.

Carbon black powder often contains different types of metal impurities, a flaw that many deem undesirable. But these metals oxidise when struck in air by a focused laser beam, and then carbon atoms get mixed into the oxidised metal. This process allows electrons in the material to have more energy to hop to different electronic states and emit different colours during the hopping process

At the same time, the heated material changes in its physical form, too. With a scanning focussed laser beam, fascinating and colourful micro-patterns are readily created on the sample. By changing the environment in which the patterning process takes place, fluorescence colour from the carbon black powder can be adjusted. 

An example is illustrated in the above image. NUS researchers used the same technique to create a beautiful butterfly pattern. This is the first time such a phenomenon has been observed using recovered carbon black. This breakthrough was reported on 19 November 2018 in the journal Nano Research.

What’s more, in the presence of an applied potential, the researchers were able to turn off or dim the fluorescence detected from the sample. This, coupled with the ability to transfer the material onto flexible, transparent films, means the ‘new’ material has even greater potential. It could be used as a flexible and transparent multi-colour fluorescence display, with the choice of turning off the fluorescence display at the user’s discretion. 

This work in its own unique way is an upcycling project at the micro- or nanoscale. However, this process is not limited by its scale. Due to the flexibility of the process, large-scale macro-fluorescence displays could also be achieved in future. The findings of the researchers thus provide a simple means to turn an affordable and abundant material – recovered carbon black – into something useful and beautiful.