Although LEDs have inspired a new generation of electronics, luminescent materials consume a fair amount of energy and have relative short lifespans. Certain inorganic metals show promise to overcome these problems, but they are rare, expensive to process, and possibly toxic.
Researchers in China recently presented an alternative on the Chem journal by revealing a group of metal free phosphorescent molecules that persistently and efficiently glow with different colors at room temperature. The team estimates that these molecules could be three times more efficient than fluorescent organic LEDs.
Although phosphorescence from organic compounds has previously been observed, this is at extremely low temperatures and in the absence of oxygen. Practical applications within these parameters are severely limited in scope. Room temperature phosphorescence (RTP) is a challenge given that physical vibrations and oxygen interfere with the facility of organic phosphorescent molecules to radiate light.
Ben Zhong Tang, a chemist at the Hong Kong University of Science & Technology, and the South China University of Technology and senior author of the paper, explains that although organic RTP systems are challenging to develop, the fact that they can be tailored and their wider availability are desirable. The paper reports on pure organic RTP molecules with long lifetimes and high efficiencies. These should help promote basic study and practical applications of RTP processes.
Pure organic room temperature phosphorescence molecules shown in both excited and unexcited states. (Video credit: Weijun Zhao/HKUST)
The challenge was overcome by Weijun Zhao, Tang and Zikai He, graduate students at the Hong Kong University of Science & Technology, by modeling how organic RTP systems behave.
Using this information, they designed and manufactured five aromatic molecules containing carbonyl. These molecules stay excited and emit light for up to 230 milliseconds, and can be tuned to glow from blue to orange-red. Other groups investigating the problem had focused more on blocking the phosphors’ non-radiative decays.
Tang hopes they can continually tweak these engineered phosphors to meet the requirements for light sensitive switches and sensors. Using their model or structural design principle, they will try to develop RTP systems with an efficiency of up to 100% and a lifetime of up to seconds. They also plan to work on the development of RTP molecules and polymers with the potential of being used in high tech applications such as afterglow organic LEDs, optical recording, anti-counterfeiting and bio imaging.
Research has been published in the journal Chem.