Future of Organic glow in the dark Materials

Researchers from Kyushu University in Japan are improving the flexibility and transparency of the product. This cheaper and easier to manufacture glow in the dark paint has also been applied. In a breakthrough demonstration, they were able to achieve organic light that lasted more than one hour. This organic glow in the dark materials can be used for new applications such as bioimaging.

Based on a process called permanent luminescence, glow in the dark materials act by slowly releasing energy absorbed from ambient light. Dark commodities in advertisements are used for watches and emergency signs, based on inorganic materials, including rare metals such as enamel and enamel. However, these materials are expensive and require high temperatures to produce and disperse light – not transparent – when ground into a powder coating.

Carbon-based organic glow in the dark materials – similar to those used in plastics and pigments – can overcome many of these disadvantages. They can be excellent light emitters and are already widely used in organic light-emitting diodes (OLEDs). But achieving long-lived emission has proved difficult: the longest emission from organics under indoor lighting at room temperature was, until now, only a few minutes.

Japanese Researchers have now broken through this limit using simple mixtures of two molecules. In films formed by melting together molecules that donate electrons and molecules that accept electrons, the researchers demonstrated light emission from organic materials that lasted for over an hour, without the need for intense light sources or low temperatures.

“Many organic materials can use energy absorbed from light to emit light of a different color, but this emission is generally fast because the energy is stored directly on the molecule that produces the emission,” explains Ryota Kabe, lead author of a paper in Nature on this research. “By contrast, our mixtures store the energy in electrical charges separated over a longer distance. This additional step allows us to greatly slow down the release of the energy as light, thereby achieving the glow-in-the-dark effect.”

In these mixtures, absorption of light by an electron-accepting molecule, or acceptor, gives the molecule extra energy that it can use to remove an electron from an electron-donating molecule, or donor. This transfer of a negatively-charged electron from the donor to the acceptor is effectively the same as transferring a positive charge from the acceptor to the donor.

The extra electron on the acceptor can then hop to other acceptors and move away from the positively charged donor, resulting in the separation of positive and negative charges. These separated charges gradually combine again – some slowly and some more quickly – to release their energy as light over the span of almost an hour.

The mixtures and processes are similar to those found in organic solar cells and OLEDs. The separated charges build up like in a solar cell but have nowhere to escape to and so eventually recombine to emit light like an OLED. The key difference in the newly developed mixtures is that the charges can exist in a separated state for very long periods of times.

“With organics glow in the dark materials, we have a great opportunity to reduce the cost of glow-in-the-dark materials, so the first place we expect to see an impact is large-area applications, such as glowing corridors or roadways for added safety,” “After that, we can start thinking about exploiting the versatility of organic materials to develop glow-in-the-dark fabrics and windows, or even bio-compatible probes for medical imaging.”

The first challenge to overcome on the road to practical applications is the sensitivity of the process to oxygen and water. Protective barriers are already used in organic electronics and inorganic glow-in-the-dark materials, so the researchers are confident that a solution can be found. At the same time, they are also looking into new molecular structures to increase the emission duration and efficiency, as well as to change the color of the emitted light.

This story is adapted from material from Kyushu University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.