Phosphorescent material inspired by glowing wood

Scientists from Northeast Forestry University and the University of Bath have harnessed the natural ability of wood to faintly glow to develop a new sustainable phosphorescent material that could potentially be used in a wide number of applications, from medical imaging and optical sensing to ‘glow in the dark’ dyes and paints.

Room-temperature phosphorescence (RTP) is when a material absorbs energy with a short wavelength (such as UV light) and then emits it as visible light. This contrasts with fluorescent materials, which immediately emit the light again and stop glowing when the light is switched off.

The researchers found that basswood naturally and weakly phosphoresces, releasing light for a few milliseconds due to lignin, a major component of wood, being trapped within a 3D matrix of cellulose. This inspired them to mimic the glowing properties by crosslinking lignin within a 3D polymer network, which caused it to glow visibly for around one second.

They found by tweaking the cavity sizes within the network, and varying drying times of the polymer, they could alter the duration of the phosphorescence. The results have been published in the journal Cell Reports: Physical Science.

“All lignin glows weakly, but most of the light energy is lost by vibration or movement of the lignin molecules, meaning it isn’t clearly visible to the naked eye,” said Professor Tony James, from the University of Bath’s Centre for Sustainable Circular Technologies.

“We’ve found that immobilising the lignin in an acrylic polymer means more energy is emitted as light — in other words, the less it rattles about, the more it glows.

“Most current phosphorescent materials are either toxic or difficult to prepare, so we wanted to develop a new material that overcame these limitations.”

To demonstrate the new material, the team used it to dye threads that could be used in luminescent textiles. This has potential use for the easy identification and the anti-counterfeiting protection of luxury textiles or bags.

“We think this work will not only provide a new option for sustainable afterglow materials but is also a new route for the value-added utilisation of lignin, which is the main naturally occurring aromatic polymer, and the pulping industry produces 60 million tons per year,” said lead corresponding author Professor Zhijun Chen, from Northeast Forestry University.

Prof James concluded, “Although there is room for improvement, our new material shows great potential for making a more stable, sustainable, biodegradable non-toxic phosphorescent material that could be used in a range of applications.”

Image caption: The leaves on the left were embroidered using fluorescent thread which glows under UV light. The leaves on the right glow briefly after the UV lamp has been switched off.

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