Towards phosphorous materials that illuminate our cities?

This article was originally published on the magazine’s website A knowledgeable magazine from annual reviews and translated with their kind permission.

Around the year 1603, Vincenzo Casiarollo, an Italian shoemaker and amateur chemist, tried to melt a particularly dense stone that he found on the slopes of Mount Paderno, near Bologna. He did not get gold, silver, or any other precious metals as he had hoped. But after cooling the stone, Casciarulo made an interesting discovery: if he exposed the material to sunlight and then moved it into a dark room, the stone glowed.

This was the Bologna Stone. The first industrially prepared fixed lighting material. Many others followed, and today continuous luminaires are used for decoration, emergency lighting, sidewalk signs, and medical imaging.

One day, they could give us bright cities that stay cooler and use less electricity.

a A new generation of lighting materials It could cool cities by re-emitting light that would otherwise have turned into heat. It can also reduce energy consumption, since illuminated sidewalks, illuminated road signs or even illuminated buildings can replace part of the general lighting. Some European cities have already installed luminous cycle tracks, and some researchers have studied the use of Luminous paint for road marking.

“It’s better for the environment,” says Paul Birdal, a now retired environmental physicist from Lawrence Berkeley National Laboratory in Berkeley, California. “If the technology can be improved, we can use less energy…. It’s an interesting thing to do.”

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Bologna stone, a form of the mineral barite, fascinated the natural philosophers of the time, but was not particularly useful at all. But in the 1990s, chemists developed new types of photosensitive materials, such as strontium aluminate, that retain a strong glow for hours after being exposed to light. Most of these new materials emit a blue or green glow, but a few are yellow, red, or orange.

These photonic materials work by “trapping” the energy of a photon and then re-emitting that energy as light of a lower wavelength. Sometimes light is emitted instantly, as in the case of a fluorescent bulb. Other materials, called continuous LEDs, store energy longer and emit more slowly.

More than 250 types of luminescent materials have been identified. They are grouped above according to a) trace substances that serve as the luminescent center; b) the host compound. c) The color that the substance emits.

These materials that glow brightly for hours open up possibilities, such as “glow-in-the-dark” cities lit by sidewalks and luminous buildings. as 19% of global energy consumption for lightingin Europe, About 1.6% is for general lightingthe potential energy savings are significant, write Ana Laura Becilo, a building engineer, and colleagues at 2021 Annual Review of Materials Research.

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One problem with this approach is that most luminaires do not glow all night long. Better materials could help solve this problem, says Becilo, of the University of Perugia, who studies energy-efficient building materials. In the meantime, the existing materials could be combined with electric lighting that would run long enough to recharge the road signs before shutting down again.

Luminous paint can also provide illumination for outdoor areas. The Pisello laboratory developed such a luminous paint and, In the 2019 report, simulating what would happen if he drew a highway near a train station with her. According to scientists, by glowing all night, the coating will reduce the energy required for lighting by about 27% in the vicinity.

If it raises fears that entire cities will light up all night long and exacerbation of light pollutionMr. Besilo thinks this is unlikely. Luminaires will likely only replace the existing lighting, and not increase it. The color of the luminous materials can be chosen to avoid blue frequencies that have been shown to be particularly harmful to wildlife.

Luminescent materials can also help combat the so-called urban heat island effect. Roofs and sidewalks absorb and emit the sun’s energy in the form of heat, causing summer temperatures in the city to rise to 7.7°C higher than the surrounding countryside. These high temperatures pose potential health risks and also lead to increased energy consumption to cool buildings.

The most common solution is the use of “cold” materials that reflect light, such as white paint and light-colored asphalt. It turns out that adding luminescent materials can be more beneficial.

In the laboratory of Lawrence Berkeley, Mr. Birdal and His team tried synthetic sapphire, a substance that glows in sunlight, to make a colorful coating that stays cool. In a first experiment, they found that a sapphire-dyed surface was kept cooler in the sun than a similar-colored material that lacked this particular dye.

Pisello laboratory went further Adding many aurora materials to concretethat is, substances that store light energy and slowly recover it. Compared to non-illuminated roofs of the same color, the best of them is to reduce the ambient air temperature by 3.3 ° C on sunny days.

“you can make [une surface] Reflective as possible. But can we get past that? The idea is that maybe you can take it one step further by using continuous luminescence as another way to transfer energy outward… That’s interesting, says Patrick E. Phelan, a mechanical engineer at Arizona State University, Co-author of an article on the urban heat island effect published in the annual Journal of Environment and Resources.

There are 250 known luminescent materials, many of which have not yet been studied for practical applications. Pisello sees the potential for glowing paints and coatings that last longer and shine brighter with more colour.

“In the short term, the simplest and most effective solution is to improve what we already have,” she explains. This includes modifying the materials to scatter the light for longer, stronger, or in different colors, making sure it continues to perform in real-world environments.

In the long term, she adds, new classes of engineering materials could be more effective. For example, one might look at “quantum dots” – tiny semiconductor particles that can be made luminous and are Already used in biological imaging – or perovskite, a material used in solar cells that has also been studied for its luminescent properties.

Translated and published with kind permission well-known magazine. The original article can be found over here.