Oct 16, 2017: A new research at Kyushu University’s Center for Organic Photonics and Electronics Research have found glow-in-the-dark paints that are more flexible and transparency, as well as cheaper and easier to manufacture.
In this groundbreaking study, light emission that lasted for more than one hour was achieved from organic materials. Due to their unique properties, these materials find new applications such as in bio-imaging.
Glow-in-the-dark materials slowly release energy absorbed from ambient light, based on a process called persistent luminescence. Glow-in-the-dark materials that are usually seen in watches and emergency signs, are gare based on inorganic compounds and include rare metals such as europium and dysprosium. However, these carbon-based organic materials are expensive, and require high temperatures to manufacture. When ground into powder for paints, these materials scatter light despite being transparent.
These organic materials are similar to those used in plastics and pigments. They are excellent emitters and are already used in OLEDs. But it was difficult to achieve long-lived emission—the longest emission from organics under indoor lighting at room temperature was only a few minutes.
In this new study, the Kyushu University researchers have overcome this limitation by using mixtures of two appropriate molecules. They melted the molecules together that give out electrons and those that accept electrons. These are called donor and acceptor molecules, and their emission last for over an hour, without the need for intense light sources or low temperatures.
When an acceptor molecule absorbs light, it gives the molecule extra energy, which can be used to remove an electron from a donor molecule. The extra electron on the acceptor molecule can then hop to other acceptor molecules and move away from the positively charged donor molecule, which results in separation of the charges. The separated charges slowly come back together, and release their energy as light over almost an hour, giving out the glow-in-the-dark effect.
Although challenges still remain, but this glow-in-the-dark materials tend to find new applications. Since these organic materials can be easily synthesized and processed, large-scale use will become cheaper. The researchers are now try to find new molecule structures to increase the emission duration and efficiency as well as to change the color.
Source: Kyushu University