Have you ever been to a  bowling alley or roller rink and noticed that your teeth  glow under the blacklight?

Or worse, maybe your friend’s  teeth glow and yours don’t, which sends you running to  buy some whitening toothpaste? That cool glowing phenomenon  is called fluorescence, and it was discovered and named  after a mineral called fluorite.

Not fluoride! Fluorite! But fluorescence has far more sophisticated uses than turning your shoelaces  and white T-shirt neon purple.

Let me introduce you to the crystal that opened our eyes to a whole new field of science. [♪ INTRO] Before we get to fluorite, I want  to shed some light on fluorescence. It’s defined as the emission of light after an object has absorbed light  of a different frequency. All light contains energy, and when  fluorescent molecules get hit by that energy, their electrons absorb  it and start to get really excited.

Excited electrons move up an  energy level, which literally means that they jump farther away  from the nucleus of their atom. Being close to the nucleus tends  to keep an electron kind of grounded, so being farther away  puts them in a higher energy state. Excited electrons have a bit  more energy than they used to.

But everything in nature wants  to be at rest whenever possible, so the electrons dump their  excess energy almost immediately and sink back into their comfort zone. I never thought I would  relate so much to an electron. Energy can’t be created or destroyed, though.

It has to go somewhere. So when  electrons release all that energy and go back to bed, that energy  gets released in the form of light. Here’s the thing about fluorescence, though.

As the electrons relax, they use some of the energy they gained to do it. And that means that when they drop back down, they do so with less energy  than the light that hit them. What that means is that the wavelength of light that gets emitted by the  fluorescent particles is longer than the wavelength of light that  excited them in the first place.

Wavelength affects a lot  of the properties of light. In visible light, we usually  think of wavelength as color. Blues and violets have shorter  wavelengths, with higher energy.

Reds have longer wavelengths, and less energy. We can’t see wavelengths that  are too red or too violet– wavelengths that we call  infrared or ultraviolet light. Blacklights emit ultraviolet  light, which has a lot of energy and wavelengths too short for our eyes to see.

But when the UV rays of a  blacklight hit a white T-shirt, they excite the T-shirt’s electrons. And when they drop back down at a lower energy, they make that pretty purple glow that we can see. Now, you notice that when  you turn off a blacklight, the glowing stops.

This  makes fluorescence different from another shiny phenomenon, phosphorescence. Phosphorescence is responsible for glow-in-the-dark paints and plastics, like what’s used in those green glowing stars you might have had in your childhood bedroom. Or all of my son’s shirts.

He has so many shirts that glow  so bright he can’t even sleep. He has to like cover them up,  or they make the room glow! Both fluorescence and phosphorescence  work with the same principle of excited light, but instead of  getting excited up to a higher energy level and immediately dropping  down, phosphorescent electrons generally stay excited for a bit  longer and burn their energy over time.

There are some exceptions, but that’s a good way to tell them apart in most cases. We’ve known about fluorescence for a long time, actually way longer than UV  lights have been a thing. The Aztecs were the first to notice  it, observing that a medicine they used to make to treat urinary  disorders had an opalescent glow.

Then, in the 1800s, European researchers started fiddling with fluorescent materials and came up with various hypotheses about what was happening. In 1852, the physicist George Gabriel Stokes wrote extensively about the  phenomenon, and was the first to name it “fluorescence”, after his  main study material, fluorite. But fluorite definitely isn’t the only fluorescent material out there, and we’ve come up with tons of ways to take advantage of  this brilliant phenomenon.

The biggest use is probably the most obvious, we use fluorescence to make fluorescent lights. Yeah! That’s why they call them that!

And of course, we also use it for blacklights and other party trick applications. But we don’t just use fluorescence  for fun, or to see in the dark. Fluorescence is a major cornerstone  of a ton of research applications.

For example, we can use fluorescence spectroscopy to learn more about the physical properties of chemicals based on how they emit light. And we can use fluorescent dyes to track and label biological molecules  in fluorescence microscopy, allowing us to see into cells and tissue. Scientists have gotten so good at the whole fluorescent dye thing that we can even make dyes that react to specific wavelengths of light, so that we can take a look at multiple molecules in the same cell in one imaging section.

This is also how we do some diagnostic tests. There are tests where they break up the genes– this isn’t in the script– There are tests where they break up the molecules of the genetic code and then  they label individual areas of the DNA, and if that DNA is present, then the– The thing will stick to it, and  then they shine a light at it, and if it glows that specific  light when they shine it with a specific wavelength,  you know that that area of genetic code is there. So you can test not just for  the presence of a disease, but for the presence of  specific strains of a disease.

Which is very cool Some fluorescent dyes are gentle enough that they can be introduced to cells  while the cells are still alive, letting us take live images or  videos of biological processes. At least one fluorescent  compound, indocyanine green, has even been FDA-approved and can be given to patients for medical imaging purposes. There are even some cancer surgeries that use fluorescence to determine  if they got the whole tumor out.

And there are clinical trials  looking for ways to use topical fluorescent compounds to  find tumors in the first place. You probably see fluorescent paints and dyes on all sorts of things every  day, and those cool things are here lighting up our world thanks to fluorite. But fluorite isn’t just an inspiration.

Many of these technologies actually  use it in their tools or equipment. For example, fluorite is used  in lenses for fluorescence microscopy because it’s  transparent to ultraviolet light. And some cameras and telescopes use fluorite lenses for the same reason.

So the same mineral that helped  us understand a core phenomenon of light lets us use that property  to see the world in a new way! That is a crystal I give a glowing review. And if you’re a SciShow Rocks Box subscriber, get your blacklight ready, because  this month’s mineral is fluorite.

Subscribers will get a hunk  of the crystal that taught us how to give laser tag arenas  everywhere that eerie, neon glow. Not a subscriber? Visit  SciShow.

Rocks to learn more, and thank you for watching! [♪ OUTRO]