When I was a child, my mother glued dozens of glow-in-the-dark stars on my bedroom ceiling. Each night I gazed in awe at my wonderful personal galaxy. The mystique behind the beautiful glow made it that much more appealing. But even knowing the physics of fluorescence, the phenomena still has a powerful pull. Materials that glow are simply emitting light energy previously absorbed from their surroundings.
Fluorescence and phosphorescence are two similar yet distinct terms that describe how light is emitted from a material, a phenomenon known as photoluminescence. When light is absorbed by a photo-luminescent material, like phosphor, the electrons are excited and jump to higher energy states. Fluorescence occurs when those excited electrons immediately relax to their ground state, returning that light energy to the environment.
Phosphorescence occurs when the electrons' absorbed energy not only causes the electrons to become excited, but also changes the electron spin state. This doubly altered electron is now a slave to the complex rules of quantum mechanics and must retain the light energy until it has achieved a stable state in which to relax. This allows the material to retain the light for significantly longer periods of time before relaxing. Materials that glow are usually both fluorescent and phosphorescent simultaneously, accounting for the nearly synonymous use of the terms (Boundless 2016). The power of light which solar energy can generate is truly breathtaking.
Harnessing fluorescence and phosphorescence for our streets
My intrigue in everything photo-luminescent is about to be satisfied beyond my wildest imaginings, due to a recent invention by Dr. Jose Carlos Rubio at the University of San Nicolas Hidalgo in Mexico. Dr. Carlos Rubio has successfully created glow-in-the-dark cement after nine years of research and development. This recently patented technology retains the functionality of cement but removes the opaque crystalline by-product microstructure, allowing phosphorescent materials to be seen (Elderidge 2016). The cement “charges” to full capacity in only ten minutes of exposure to natural light and will glow for up to 12 hours each night. The material’s fluorescence is also quite durable to the test of time. The brightness will reduce by only 1-2% annually and maintain over 60% capacity for greater than 20 years (Balogh 2016).
The applications of glow-in-the-dark cement are seemingly endless. It is evident that the technology will be useful in both public and private spaces. This cement could revolutionize nightlife in urban environments by reducing streetlights on sidewalks and adding illumination to crosswalks. While this cement will not completely eliminate nighttime fixtures, it will significantly cut down the amount of electricity burned every night. Major urban destinations like New York City, Shanghai, London, and Los Angeles could significantly reduce their carbon footprint by utilizing this new material. Cities close to the Earth’s poles could also benefit from sustainable light during winter months that suffer painfully short days.
Additionally, consider the beautiful and artistic applications of this technology in private space. This cement is currently advertised for driveways, walkways, pool decks, indoor and outdoor stairways, as well as for concrete sinks and appliances. Custom installations result in beautiful artistic designs creating a wonderland of photo-luminescence. The future is brighter than you might have thought. I, for one, cannot wait to stroll down phosphorescent streets in a glowing future.