Scientists from the University of Bath and North East Forestry University, China, have developed a durable phosphorescent material with potential applications ranging from medical imaging to glow in the dark dyes and paints. The material is inspired by the natural phosphorescence of wood.
Fluorescent materials occur in nature, including in some jellyfish, corals and tree frogs. Visible fluorescence occurs when these materials absorb energy at a short wavelength, such as UV frequencies, and radiate the energy as visible light. Unlike room temperature phosphorescence (RTP), the fluorescence stops immediately and stops when the light source is turned off.
The new study examined the natural RTP of lignin, a group of polymers that give wood its rigid structure. It found that basswood (also known as American linden) naturally and weakly phosphorescent, releasing light for a few milliseconds, because lignin is locked in a 3D matrix of cellulose.
This inspired the research team to mimic the phosphorescent properties by cross-linking lignin in a 3D polymer network; they were able to make it glow visibly for about a second.
By tweaking the cavity sizes within the polymer network and varying the polymer’s drying times, they were able to fine-tune the duration of the anneal.
“All lignin glows weakly, but most of the light energy is lost through motional vibrations of the lignin molecules, meaning it is not clearly visible to the naked eye,” said Professor Tony James of the University of Bath’s Center for Sustainable Circular Technologies. . “We have found that immobilization of the lignin in an acrylic polymer means that more energy is emitted as light; in other words, the less it rattles, the more it glows.
“Most current phosphorescent materials are toxic or difficult to prepare, so we wanted to develop a new material that overcomes these limitations. While there is room for improvement, our new material shows great potential for making a more stable, sustainable, biodegradable non-toxic phosphorescent material that can be used in a range of applications.”
In a demonstration of their new material, the scientists coated cotton threads with a dye the material used and used them for luminous embroidery. They suggest this could help identify and protect against counterfeiting of luxury textiles and handbags. Other applications may include medical imaging, optical detection and glowing paints.
Professor Zhijun Chen from the Wood Construction Center of Northeast Forestry University commented: “It is indeed an unexpected and interesting discovery. We believe that this work will not only provide a new option for sustainable afterglow materials, but also a new route for using value added lignin, the main naturally occurring aromatic polymer [used in the pulp industry].