A team at MIT has developed a technique for getting plants to behave like glow-in-the-dark toys—they can absorb light, store it, and then radiate it back out.
This team has been working on glowing plants for a while now; in 2019 they debuted plants that were treated with an enzyme based on the same chemical that make fireflies glow (previously). This new trick works via nanoparticles made of strontium aluminate, which can absorb light.
The scientists coated the particles in a layer of silica to protect the plants from damage, and injected them into the spongy outer layer of the plants called the mesophyll.
When the scientists shone a light on the leaves, the plants absorbed it and radiated it back out brightly "for several minutes". As MIT's press office notes in its release:
This film can absorb photons either from sunlight or an LED. The researchers showed that after 10 seconds of blue LED exposure, their plants could emit light for about an hour. The light was brightest for the first five minutes and then gradually diminished. The plants can be continually recharged for at least two weeks, as the team demonstrated during an experimental exhibition at the Smithsonian Institute of Design in 2019. [snip]
The MIT researchers found that the "light capacitor" approach can work in many different plant species, including basil, watercress, and tobacco, the researchers found. They also showed that they could illuminate the leaves of a plant called the Thailand elephant ear, which can be more than a foot wide — a size that could make the plants useful as an outdoor lighting source.
Thus far it looks like the nanoparticles do not harm the plant or interrupt its normal photosynthesis, but this is early days, so obviously lots more study will be needed. But assuming it doesn't cause the plants long-term harm — or, y'know, cause them to go all "nature will find a way" and spawn generations of homicidal ambulatory bioluminescent triffids (probably unlikely; this technique isn't a form of genetic engineering) — it's an intriguing way to create a potentially very-low-carbon, and gorgeous, source of ambient light.
Their unpaywalled (and nicely written) paper describing the research is here.