Turning to trees for sustainable photoluminescence

Photoluminescent materials can absorb and re-emit light - for instance, a glow-in-the-dark sticker - and these materials are essential for many modern technologies. Here, we developed photoluminescent materials solely based on a waste product – lignin from the pulp-and-paper industry and the amino acid histidine, without requiring heavy metals or halogens such as bromine, which are commonly needed.

Many of today’s display emitters use heavy metals or halogenated frameworks—for example, cadmium-based quantum dots, platinum/iridium complexes, or lanthanide systems—and they’re often made with hazardous reagents and high-temperature steps. That combination raises three concerns: (1) Consumer risk is generally low in normal use because materials are encapsulated, but damage or improper disposal can create exposure pathways; (2) worker risk comes from handling toxic metal salts, corrosive/irritant chemicals, and volatile solvents during manufacturing; and (3) environmental impacts stem from metal mining/refining, energy-intensive processing, and e-waste at end-of-life.

To make paper, you remove the cellulose, but the remains are rich in lignin, which is often burnt for energy. However, lignin is the most abundant natural material that contains aromatic groups, which are an important input to the chemical industry. Currently, it’s usually obtained from petroleum. So unlocking the potential of lignin is an important step away from a petroleum-based society.

Here, lignin plays an important role in the material’s photoluminescent properties, specifically due to its aromatic character (besides some other features), so demonstrating that a “natural” material combined with another natural material – an amino acid that is present in protein - is a cool demonstration of what natural materials are capable of.

What’s exciting about this is the following: The developed materials are not yet optimized. So when we say the afterglow is only about 300 milliseconds, the hope is that by varying composition and input, by manipulating both “ingredients” so to speak, both photoluminescent properties (fluorescence and phosphorescence) can be improved. Also, there are different kinds of lignin, so exploring the range of different lignins may also aid in the optimization of the system. In a way, this study can hopefully lay the groundwork and start the momentum to develop other renewably sourced and non-toxic photoluminescent materials.