As efficient as light emitting diodes (LEDs) have made lighting, there is plenty of potential for further improvement. Even highly efficient LED lights waste a lot of the electricity they consume as heat. The quest to produce still more light using less energy has been caught between two classes of molecules, each with different drawbacks.
The easiest phosphorescent molecules to make rely on metals that would be expensive, and often toxic, if used widely. Organic versions work best at impractically low temperatures, and have to be protected from oxygen.
So Professor Ben Zhong Tang's announcement of the creation of a class of room-temperature phosphorescent (RTP) organic molecules could be a game-changer. His team of chemists has produced a set of organic molecules that glow at room temperature and consume very little energy to do so. They even come in a range of attractive colors, although pretty lights represent a small fraction of their potential.
Tang and his graduate students at the Hong Kong University of Science and Technology started by considering what organic molecules might light up at room temperature, modeled the structures required for best performance based on the energy levels of electron orbitals, and then set out to make them.
They were able to produce five aromatic molecules that emit light after they have been excited. The longest of these lasts for 230 milliseconds, less than a quarter of a second, after excitation ceases. Short as this sounds, it is a huge increase on many past efforts.
With modification, the molecules can be made to glow along much of the visible spectrum, from blue to the wavelengths where orange and red meet. The molecules in question convert up to 36 percent of the energy applied to them into light, making them three times as efficient as a fluorescent organic Light Emitting Diodes (LEDs).
Reporting their results in Chem, Tang and his colleagues admit that neither the lifetime nor the efficiency set a record, but since there is a trade-off between these two, the combination is significant, particularly for a first effort.
Having demonstrated that their molecules can perform as modeled, Tang expressed an intention to extend the glow time, and improve the efficiency to the point where 100 percent of the energy input is released as light.
The relative efficiency of LEDs compared to incandescent bulbs or even fluorescent bulbs, has played a big part in North America and Europe's falling greenhouse emissions. The impact has been even greater in Africa and southern Asia, however. In combination with tiny solar panels, this technology has brought light to millions who were previously dependent on candles and kerosene lamps – a frequently life-changing development.
Improvements in efficiency could take this revolution further. Tang and his colleagues also see potential in more high-tech areas, referring to the possibility of using their molecules for everything from bioimaging to anti-counterfeiting measures.