View transcript
- My name is Kathleen and I'm part of the programming team here at the Exploratorium. Is it anybody's first time at the Exploratorium who didn't answer that question in the previous talk? Oh, welcome, we're always thrilled to have new visitors. And we also wanna welcome back all of our members. We're really excited to be able to be back to doing our fun, engaging, after dark programming which we do every single week. So we hope we see some of you folks who are here for your first time coming back again in the future. And now you'll be hearing from one of our staff educators. And when introducing Ron, he has so many fun facts that I love picking from some of those. But I think one of the most essential ones, 'cause it's timely, is the Exploratorium was founded 52 years ago and a month ago, Ron celebrated his 50th anniversary as an employee. So let's celebrate Ron's golden anniversary by watching him with great attention, attentiveness to his jokes, laugh, as well as responses to his questions. Here's Ron.

- Thank you, Kathleen. I always thought education is like 95% standup and 5% facts. Oh, and I didn't get my slides in here. But that's all right, we'll just go straight to the ad 'cause I'm so used to doing this online now. Oh, we didn't have a sound. Okay, no problem. Tonight what I'm gonna talk about is this part of a series that we normally do called full spectrum science, which we haven't done a lot of during the pandemic. But we've done a few online versions in the hope that all of our audience out on the internet there has had a chance to take a look at them on the Exploratorium's YouTube channel and other media distribution channels. Today I wanna talk about glowing things. And the first thing I wanna really talk about is gas excitation, 'cause that's a lot of the stuff that we've been seeing is exciting gases to glow. And, oh well, I'm sorry, I have to, I'm not seeing my notes here. I apologize for this, I have to change something. Something's not working properly. I apologize for this. Oh, I think I'm gonna have to do it without it. Let's see. Let's just go on. I'm just gonna do it off the top of my head 'cause I know this well enough. So gas excitation here, we see three different things of gas excitation. That big yellow lamp you see there is a sodium vapor lamp or excited sodium atoms are caused to give off their light. Then we also have a neon sign. And actually by the way, neon. This is the only color right here that's neon is the red thing that says route, the rest of it is all kind of mercury-based sign, fluorescent signs. And then the last thing, speaking of mercury, is this mercury germicidal lamp with its beautiful baby blue color. Let's talk about that gas excitation. We have to go atomic here. So this is a very, very, very simple model of an atom. Obviously, it doesn't really look like that, but it's a useful thing to talk about, used to talk about how light is given off by atoms. So we have here your basic simple atom with the nucleus in the center surrounded by electrons, and those electrons occur in shells. And those shells, where those shells are at are the energy levels, are determined by quantum mechanics. And we're not going to talk about quantum mechanics tonight, but suffice it to say that these energy levels are defined by quantum mechanics. And the electrons can only exist in those shells. It's like walking up a set of stairs. You have to stick to the stairs, you can't go up one and a half stairs. You can't exist between stairs. Same similarly in an atom, the electrons can only exist at these specific energy levels. And there's a difference in energy between each level with higher energy. Lower energy orbits and closer to the nucleus and higher energy orbits further out. So how does this happen? You can excite an electron, you have to give it energy and you can do that several ways. You can heat atoms up, you can shine light at atoms and cause them to jump up, or you can pass electricity through a gas. So let's do that in this case, let's pass electricity through the atom. And of course electricity is just electrons too but if you notice we've excited the electron up to a higher energy level there. Now most atoms in an excited state, it's like coyote, once he walks off the cliff, he looks down and you have to instantly fall. So this electron normally will fall down and give off its light, give off its energy as a little pulse of light called a photon. Just a little pulse of light. Now atoms have lots of energy levels, I'm showing you four of them right here. There's a lot more of them out there. And so the energy difference, there's lots of different jumps that are possible here that you can get lots of different energy jumps and therefore different colors of light. Higher energy jumps are more violent and lower energy jumps are more red. Look towards that end of the spectrum. So for instance, you might have a big jump which give off an ultraviolet photon. Or you might have a small jump that gives off a red photon. Or anywhere in between, you can have various jumps. So, an atom can give off very specific colors depending on the energy jump. I think I have one more here, let's have a green. Yeah, there it is. And these colors that every atom can give off are very, very specific. We're gonna look at some real colors being given off by gases now, by excited atoms and those glasses I've given you have a piece of plastic in that you look through, that's called diffraction grating. When we look at a gas lamp like this, we need to be able to take that light from that lamp and sort it out by color. And that's what those glasses are gonna do for you, they're light sorters. The diffraction gratings are light sorting. And you've probably seen these before, they kinda make lights look like this. Actually, if you looked with a microscope at the plastic in your glasses, you don't have to put them on yet, the plastic looks like this, it has a bunch of little grooves in the plastic. And those grooves, the light bends through those grooves, diffracts, it's called, and red light bends more than violet light. And so this stuff, this diffraction grating will sort out the light. You've seen this before actually. This is what it will look like. You'll see the lamp will be in the middle and you'll see a spectrum on either side of the lamp itself. And you've seen this before, as I mentioned. Well, maybe you have. We used to have these things called CDs. Remember those? Well, they have a lot of very microscopic stripes on them. And those microscopic stripes, that is where the data comes, is on the CD, breaks the light up into colors too. That's where the colors come from when you're looking at the reflection off of a CD or a DVD, or even a Blu-ray. That's what we're gonna use. We're gonna use diffraction to look at light. So let's take a look at some gases. I have a tube here and this tube has an electrode over on this side. It has an electrode over on this side and that electrode goes through the glass. And I don't know if you can see, but inside the tube, the electrode goes into the tube. Now this tube contains the simplest gas we know of. What gas is that? Hydrogen, very good. Someone knows their periodic table. So there's hydrogen inside of here and I'm gonna put a high voltage between the two ends here of the tube and it will excite the hydrogen into glowing. So let's take a look at what that looks like. And without our glasses, I want you to see what it looks like without your glasses first. So let's turn the lights down and so you can see this glowing. That's the color of glowing hydrogen gas. Beautiful crimson color, I just love this, this is my favorite of all of the gases glowing. Now, if you put on your glasses and look through them at the lamp on this side over here or on this side over here, you will see the spectrum of hydrogen. Let's turn the lights down all the, oh, I see, the projector is still lit up a little bit. So what do you see? You see--

- Red.

- Red.

- Turquoise?

- Kind of a turquoise, a cyan color. And you see a really deep violet, right? So those three colors are the three colors that are given off by hydrogen in the visible part of the spectrum. There are other colors that you can't see. Hydrogen is giving off infrared colors and, well, can you say infrared colors? Yes, why not? And it's giving off ultraviolet colors or wavelengths, but you can't see any of those. But this pattern is given off by hydrogen and only hydrogen gives off this pattern. Wanna see another one? Okay. Let's see if I can do this in the dark. Oh, oh, there we go, a little bit of light. Okay, so this gas in this tube is the second most simple gas. Okay, periodic table people.

- Helium.

- Helium, yay! The only two gases made during the Big Bang. Now helium's gonna look a little different too without your glasses, let's look at it without glasses. That's different, isn't it? And with glasses, it has a red, it has a cyan, it has a bright yellow and it has also a violet line as well. But this is different. You wouldn't confuse hydrogen and helium if you were looking at it through your diffraction grading 'cause they're very distinct. Wanna see another one?

- Yeah.

- Okay. This one has another noble gas. It's the one that's actually under helium. Let's see if anyone knows that. I've already mentioned it by the way, neon. And you probably have seen outside, you've seen them actually bending tubes with neon gas. Now neon gas, again, looks very different than hydrogen or helium. Look at that beautiful red color. Let's look at it through our diffraction gratings. Oh, that one has a lot of lines. Mostly in the red and orange and yellow. It's very little in the green and blue, which I know are violet, which you might guess, because look at the color of the lamp. There's not a lot of blue light or green light in that. It's mostly reds, and yellows, and oranges. Very distinctive. Okay, one more?

- Yes.

- Okay. I know you just wanna see one more because this one's important too. And you've seen this one already as well. This one is way down near the bottom of the periodic table, this is mercury. So inside of here, there's a little bit of mercury and the high voltage is making it glow, this beautiful bluish color, baby blue. And you look at this, you should see a bright yellow line, a bright green line, maybe a couple of them and a bright violet line. What you're not seeing here is mercury puts out tons of colors in the ultra violet. Most of the energy put out by this lamp is actually going in the ultraviolet. Now we're gonna see why that's important a little bit later. Questions, comments? Let's turn that off. And we're gonna leave that in there 'cause I'm gonna use that later too. Okay, so let's do a quick review. Here are the four gases that we just saw. These are actually pictures I took through diffraction grating so we can compare the colors. And you can see that the hydrogen makes this red, the cyan, and the violet. And helium makes almost the same colors, but with a few extra, and especially this yellow, by the way, we'll talk about that in a moment. And neon is mainly in the reds and yellows. A couple of little weak green lines there. And mercury, yellow, green, and violet. They're distinct from each other. You can use your diffraction gratings. If you can make an element glow, you can do chemistry without even having the element there, you just have to look at the light coming from the glowing element. This is gonna be important. For instance, we can't go out 1,500 light years from the earth and collect a bottle of gas from the Orion Nebula. But we can look at its light by looking at its light. We will be able to tell that the Orion Nebula is glowing from hydrogen gas and a little bit of helium too. By looking at the Doppler shift of those colors, than having them move one way and the other because of the motion of the object itself, of a star, here's a star giving off light. And when it's moving towards this side of the screen, the waves are compressed. When it's moving away from this side of the screen, the waves are stretched out, are redder. This is bluer and redder. You can tell the motion of stars and the rotation of stars by looking at their light, by looking at the glowing light of these stars. That's how you might detect the presence of a dark exoplanet, for instance. It's pushing and pulling on the star. By looking at the life of this star, we could tell that this star was actually a supernova that exploded in 1054 AD. The Chinese saw it, wrote it down, documented it. This is called the Crab Nebula. And in the middle of that, there's a little pulsar, the very first pulsar discovered. You can also tell something about the magnetism by looking at the light, how much magnetism and what direction it's pointing. Here's the Whirlpool Galaxy. And this is a visualization showing the magnetic field in the Whirlpool Galaxy just by looking at the light coming from it. It's like sprinkling iron filings across a whole galaxy. You can see which way the magnetic field is pointing just by looking at the light. So by looking at all this glow coming from space, you can get a lot of information. Here's the Horsehead Nebula. I wonder why it's called the Horsehead Nebula. This is a dark nebula. And by looking at infrared light coming from these dark nebulas. This is in front of this glowing gas right here. You can tell a lot about the substance there as well, that this is a colder substance. So this is a picture, a loop of the sun. And what you're seeing here is glowing hydrogen gas. Remember those three colors given off by hydrogen? Red, cyan, violet? This is looking at just the red color. That red color is called hydrogen alpha. The cyan is hydrogen beta and the, we all know the Greek alphabet now, don't we? And the violet is hydrogen gamma. But this is just the red color. And just looking in that color, you can see these prominences on the edge of the sun without having to look at it during a total solar eclipse. By the way, that's the size of the earth compared to the size of the sun, so we don't wanna be close to the sun for many reasons actually. But this is again just an example of gas excitation. This should be the color of the hydrogen tube you saw but we're only looking at the red color, remember? Here, you're seeing during, this is a photo I took during a total solar eclipse. And look at the prominences you can see here, that is the same color, that crimson color of the hydrogen gas you saw glowing here. That's when I first saw, my first total solar eclipse, I was like, "Wow, that color," and I went, "Oh, that color." Now I know what that is, that's hydrogen gas. There must be hydrogen gas in the sun. By the way, the sun is mostly hydrogen but there's also helium there. Here's a very detailed slide of the spectrum of the sun, from red all the way through violet. It's so detailed they had to put it in strips and pile them on top of each other. And each one of these dark lines is an element in the outer atmosphere of the sun that's cooler and absorbing the same color light from the hot part of the sun that's giving off just white light. So this is called an absorption spectrum. You are seeing an emission spectrum from the lamps here, but it's the same idea. Elements absorb the same colors that they emit. And you can see here, there's magnesium, and chromium, and iron, and barium, and titanium. I'm just reading some of the chemical symbols here. I've only labeled a few of the lines too. Most of those lines are because of iron but it's a beautiful spectrum of the sun. If you take your glasses and put them over your camera lens, you can take pictures of the spectra of things. And if you do that during a total solar eclipse, just as the last bit of the atmosphere is disappearing there, you see this, and these are all because of chemical elements glowing in the outer atmosphere of the sun. We've seen some of these before, actually we've seen most of them before. Hydrogen, the red hydrogen, alpha helium, this yellow color is helium. Some greenish magnesium, hydrogen again here and hydrogen again here. And by the way, helium was discovered on the sun before it was discovered on the earth. We didn't even know about helium until it was discovered on the sun. It's not part of our atmosphere. Helium atoms move too fast and they're moving faster than escape velocity from the earth. So they bumble their way up to the top of the atmosphere and disappear into the solar system. Ever wanna launch a spacecraft? Just pop a helium balloon. Billions and trillions of spacecraft that you're launching. I'm against helium balloons, by the way, because helium is not part of our atmosphere. It is a non-renewable resource, it has to be mined. It comes from underground. By mining, I don't mean that these, you know, you get these big burly guys with hats, with the lamps on them, they go down the elevator during the day and at the end of the day they come up with high squeaky voices. No, it comes from gas and oil extraction. So it's a by-product of a gas extraction, so it's a non-renewable resource. And I would rather not use it in balloons and have it available for MRI machines and things like that. But we should be using hydrogen in balloons, let's face it. Not only does it, it has better lift, but the explosive properties make it a much more interesting prospect. Helium was actually named after Helios, the sun god because it was discovered on the sun. If you put salts in a flame, the flame will glow with the color of the spectrum of that particular element. So here we have sodium. And here, I believe this is probably copper. This is probably strontium, and this is lithium. And I think this may be calcium. Different elements, again, give off different colors. And you can do it in a flame. If there's any chemists here, you know about, this is called the flame test. You just look at the spectrum of the flame. This was an art piece. I can take my mask off. This is an art piece that was made by one of our artists, Earl Sterling, where he had gas, propane gas coming up through a sand. And he sprinkled different chemical salts in the sand and it made the colors just beautiful. So there's just a nice sculpture I thought I'd show there, throw in there too. Gas excitation happens in lightning storms. This is a lightning storm happening at Kitt Peak Observatory, near Tucson, Arizona. And the lightning strike, just like my gas tubes over here, is going to excite the gas. And if you put your diffraction grating over your camera lens, you will get a picture of the spectrum of whatever is being excited in the atmosphere. Let's magnify in on a portion right down here. And if you look there, you're gonna find nitrogen, nitrogen, nitrogen, but you're also gonna find hydrogen. There's the red line from hydrogen. There's the violet line from hydrogen. Hydrogen? That's not part of our atmosphere, but it is. Where is their hydrogen in our atmosphere? Water vapor. And the lightning is just gonna rip that apart into hydrogen and oxygen, H2O. Here's going a little higher up in the atmosphere, the Aurora Borealis or the Aurora Australis if you happen to be living in the Southern hemisphere, is excited by particles from the sun, the solar wind. The sun exhales charged particles, mainly protons. And when they come and hit the earth, the earth's magnetic field deflect some to the north and the south polar regions. And when they crash into the upper atmosphere, they disturb those atoms and so you get the aurora. We can view them from above now, it's really cool. Here's a time-lapse movie from the International Space Station. And so it's just this time-lapse, you can also see the motion of aurora. Aurora, not stable, they move around, they're kind of look like curtains that are flapping in the breeze, beautiful. And you see the red up here and the green below, it's just incredible. Makes me wanna go on the space station except for the whole wait list and throwing up part. And if you take the spectrum of the aurora, you'll find that our atmosphere contains nitrogen, which is responsible for that reddish color, pinkish color and oxygen, which is the greenish color. Again, a very useful tool. So I wanna now talk about a different way. When I was talking about the gas in these tubes, this gas is almost at a vacuum. The atoms are far apart. It's like having two bells that are far apart. And when you ring them, they can ring in nice, clear tones. But if I bring the bells closer together, if I compress the gas in the tube and I make it maybe into a solid even so that the atoms are right next to each other, the bells do not ring very purely anymore. As a matter of fact, in a solid, the bells are more like this. And what you get is all of those energy levels interfering with each other. You don't get nice clean colors, you get this. Which is, what do we call that kind of noise? White noise, yeah. In this filament right here, these are called incandescent lamps which we're not allowed to have anymore. There's a solid tungsten filament running up the tube here. And if I put electricity through it, it will cause the tungsten filament to glow brightly. But is it gonna give off a tungsten spectrum? No, because the atoms are all close together and the energy levels are interfering with each other. It gives off white light. Check that out through your diffraction gratings. Incandescence. That's sort of what you're seeing here. If we look here, the sun, the inner layers of the sun, the photosphere is compressed gas, it's gas that's close to each other. So the surface of the sun, the visible surface of the sun gives off white light. Let's not ignore the sunspot there. It gives off white light. That white light goes through the outer atmosphere of the sun where it gets those dark lines absorbed. That part, by the way, that outer atmosphere is called the chromosphere, for color. Solid filament in a light bulb, this is a carbon arc lamp, gives off a bright white light because the carbon is going into the arc right here and the carbon is getting heated up to incandescence just like this filament is. And that bright, hot carbon is responsible for the carbon arc lamp. as it is also for a candle flame. At the bottom of the candle flame, the carbon isn't very hot yet but in the middle of the candle flame, the carbon is getting very hot. And if you hold a spoon above a candle flame it'll collect the carbon black. You can see that, you try that at home. Now I'm gonna do that experiment. Well, let's just move right on then. Let's talk now about real glowy stuff, fluorescence. You may have seen in a museum display like at the California Academy of Sciences. I don't know if they have the glowing minerals anymore but they used to have this beautiful display of glowing minerals. They have a really beautiful mineral collection of the Cal Academy. I encourage you to go and check it out. Fluorescence is a whole new phenomenon. Where else would you have seen it? If you go down and look in the gallery three, scorpions. If you've ever been out in the desert at night and you take your ultraviolet flashlight with you, you can prospect for scorpions because they glow this beautiful green color. And you can go down in gallery three and check that out. If you're a survivor of the '60s, you probably remember all those amazing blacklight posters that you could purchase in the Haight-Ashbury. Well, I think we need to talk about fluorescence. So we need to, of course, get atomic again. In fluorescence, it's not just an excitation and deexcitation, it's an excitation by a high energy photon, ultraviolet. When that happens, when we have an incoming ultraviolet photon, it can excite the atom so that the electron jumps up several levels. When it deexcites, it can go back not by giving off ultraviolet and jumping down two levels but it can jump down just one level and that might give you infrared photon. And when it jumps down the second level, it gives off maybe a green photon. And that means that we've changed ultraviolet light into greenlight. We've changed invisible light into visible light, that's fluorescence. You may be familiar with that on your television. Your television has a screen that has fluorescent phosphors on it. Anyone remember when televisions looked like this? I even added the rabbit ears here for you. This tube, this cathode ray tube, if we slice it in half, looks like this. An electron beam starts off here at the electron gun. It's deflected by these coils and can scan across the face of the tube. And on the face of the tube there are phosphors that will glow when they're excited by being hit by the electron. And these phosphors are arranged in, there's usually red, green, and blue phosphors, and they're arranged in different ways depending on what brand of television you bought. But this was I think Sony's arrangement and this was basically everybody else's. But notice red, green, and blue. And by making the electron beam, more intense or less intense, you could make the red, green, and blue spots brighter or dimmer and create any colors you wanted with red, green, and blue. Here's some phosphors that are lit. This is ultraviolet light, but on the inside of your tube, there's no real green here, I guess that's sort of green. You'd have a green phosphor, a blue phosphor and a red phosphor. Let's actually look at some fluorescent stuff 'cause I have a mess of fluorescent stuff here. Let me start off with the fluorescent lamp first. Everybody's familiar with fluorescent lamps, right? You have, this is a small one but a lot of us have these in our homes, in our garages, in our kitchens. This tube here is really the same as the tube that's in here. Inside this tube is mercury. And when you excite it, it glows in mercury colors, what? You said, no, that's white. Well, it's not really white. I have a tube here. Here's a fluorescent tube that is half coated with the powder on the inside of the tube and half uncoated. You can't buy, well, I guess you can buy this but you'll have a hard time finding this tube. This powder on the inside are phosphors. They glow when the ultraviolet light from the mercury hits them, it turns into various colors depending on the powder and converts the ultraviolet light into visible light. Let me turn this on so you can see it. Familiar? Get it, okay? But look how bright that is, how much ultraviolet light there must be inside this tube to make something that bright. Let's turn down the lights and use your diffraction gratings again. And take a look at this. Let's take the lights all the way down. Okay, so off to the side here, you should see the mercury spectrum. The yellow, the green, the violet. On the top, you're seeing the yellow, the green, the violet and you're seeing the phosphors as well. Fluorescent lights are called fluorescent lights because these phosphors are fluorescent. That's the phenomenon that's going on here, fluorescent lights. Now this is just one form of fluorescent light. They all have mercury in them so there's a little drawback. They have kind of toxic stuff in them. Of course now you can go out and get the things that look like fluorescent tubes but they really have LEDs in them. Those are not fluorescent tubes though, technically speaking. You've seen fluorescent tubes that look like this, these compact fluorescent tubes, these were supposed to be replacements for incandescent bulbs. They are much more efficient. These use about one-fifth the energy of these for the same amount of lights. But I don't have one without the coating but this has a different phosphor maybe than this one has. This is a warmer white. So if we look at that with our diffraction gratings, you'll notice there's more red in this spectrum than there was in the cool white fluorescent. So you can adjust it by adjusting the phosphors. You can adjust the color of the fluorescent light. I'm not a big fan of these compact fluorescence, I must admit, they take time to warm up. I hate that when I go into the bathroom and it takes like three minutes to get all the light. So I've replaced all of mine with LEDs. And there's no mercury problem with LEDs either. Okay. By the way, okay, here's the compact fluorescent that just makes ultraviolet light because it has a filter. So this is filtering out all the, you won't be able to see much with your glasses here, unfortunately, but I'm glowing a bit. As a matter of fact, maybe we can get everyone glowing here, let's turn. I have a ultraviolet light that's up in the rafters up here. And maybe we can get Rick to turn that one on. We were having some problems a little earlier with that but let's see if maybe that can happen. But let me look at, while that's warming up, let's get some, or maybe it won't even work, but we'll get that eventually. Let's look at some other fluorescent stuff. I love these microfiber cloths that you can buy at Costco. I'm gonna use this ultraviolet light on it. Sorry, Rick, we gotta turn the lights up and down an awful lot here. Lights down. These microfiber gloves, oh, there we go, now we're getting some light from up there, are really fluorescent. It's really turning the ultraviolet light from this flashlight into yellow light here. You notice my T-shirt is glowing and it'll glow brighter as that thing and so will you, by the way, you'll be glowing as well. My T-shirt is glowing bright white, bright blue. Why is my T-shirt glowing blue? Well, this stuff, this laundry detergent, I just happened to have some All laundry detergent. Laundry detergent is chock-full of fluorescent dye. And when you wash your tidy white tees, you are dying them at the same time with this fluorescent dye. So when you go outside with your white T-shirt on, your T-shirt is not just reflecting the light from the sun, but it's taking the sun's ultraviolet light, we know that the sun makes ultraviolet because we get sunburned, right? There we go. Not only is it taking and reflecting the white light from the sun, but it's taking the ultraviolet light from the sun and making this bright, now some of you are glowing now too I can see, is making this brighter white. As a matter of fact, I'm not just white, let's go to the marketing phase here, I'm not just white, I'm whiter than white. And that's why they use that slogan in that marketing. Okay, so what else is, oh, I have some beautiful fluorescent pastels here. These are pastels that have some lot of different color of fluorescent pigments in them, of phosphors. I have, oh, okay. Have you ever gone to a club and they stamp your hand? This stuff here is the invisible ink. It's clear. And I'm gonna put a drop of it on the back of my hand here. There we go. Ooh, it's alcohol, it's cool. Let's turn that ultraviolet light off. Everybody's been seen glowing here. You've checked out your own T-shirts hopefully. There we go. I have it on my hand here. If I use a white, I have a white flashlight right here. If I use the white flashlight, you don't see anything on my hand, okay? But if I use an ultraviolet flashlight, there it is. You can see this. Oh my, the rest of my hand is glowing 'cause I was playing with some fluorescent dyes earlier. But yeah, so that's how the club invisible ink stamps work. They're just fluorescent. Speaking of those fluorescent dyes that I was doing a little bit earlier. Let's turn on the lights again. And I have here a couple of beakers of water. And this stuff right here, which kind of looks, I don't know if you can see, it looks kind of orange, this powder, this is called fluorescein dye. And this is one of the most powerful fluorescent dyes that there is. I'm just gonna open this up and I'm going to just dip a Q-tip in here just to get a little bit of the powder on the Q-tip and then I'm gonna mix it into this water here. So look at the powder, it looks like dark brown. But watch what happens. Let's turn off the lights again and I'll do this with the lights out with the ultraviolet flashlight. Notice the powder itself is not really fluorescent. It's just that little bit of powder made this intensely fluorescent. Isn't that nice? Wanna try another one. I just happened to have another beaker, so yes, you wanna try another one, okay? I think I'm gonna need the lights back up 'cause I can't see what I'm doing. Okay, this one here is a different fluorescent dye and this is a biological stain called Rhodamine biological state. By the way, this one is gonna, well, it's gonna make it like magenta. But if you look at the powder, if you come up after and look at the powder, the powder is green. For some reason they seem to be like the compliments of what they actually look like when you have them in solution. Okay, here we go. Let's try this one here. Get a little bit of Rhodamine on that Q-tip and get my light out. Okay, here we go, here's the Rhodamine.

- Ooh.

- Ooh. The proper is ooh and ah, by the way, yeah. It's the same protocol as fireworks. Ooh and ah. Yeah, it's very cool. So that's a biological stain which is why my hand is now all stained up with it because I was playing with a little bit earlier. Okay, so that's a nice fluorescent. Things that you know about that are fluorescent. Oh, if you dissolve a turmeric in alcohol, it doesn't dissolve in water very well. I don't have any alcohol up here, but if you dissolve turmeric and alcohol, it looks like fluorescein. Let me just put the top back on the Rhodamine so I don't make a mistake. There we go. And this piece of plastic has a fluorescent dye in it. And this is actually used to detect radioactive particles. When gamma rays pass through this plastic, they make a little flash of, it makes a little flash of light, it's called a scintillator. So this is actually used in physics experiments. And I think I've got all the, oh, one more, tonic water. Tonic water, we'd probably don't even need to turn the lights out for this. Tonic water is pretty highly fluorescent. It's pretty, it has a very nice blue color to it. So go out and get yourself a UV flashlight, you can get those in a lot of places. You can make a lot of things glow. Okay. Remember these things? We're gonna talk about something that's kind of related to fluorescence. But as a kid, maybe even as an adult, in your bedroom, you may have stuck these glow-in-the-dark stars on the ceiling. And when it was time for lights out, well, lights went out sort of but some things didn't go out. This is a different phenomenon, not florescence, this is called phosphorescence. And of course the energy would dissipate eventually. The stars would get a little bit dimmer over time but phosphorescence was the ability to hold on to the energy given to it by the light from your room and then give it off slowly, phosphorescence. Because phosphoresce was the thing, the element that actually had this quality. So that's how it got its name, phosphorescence. So how does that work? We can go see it here, by the way. I know people who have their first visit here, the shadow box is a room with walls that are painted with this phosphorescent material and a camera strobe is set off and that causes the the material to glow. But if you happen to be standing in front of it at the time, well here, I just did a video today. Here's one of our explainers. Your shadow gets stuck to the wall because it wasn't exposed, it didn't start glowing. And sort of Peter Panish, isn't it? You get separated from your shadow. This phosphorescent glow, let's talk about how that happens but we gotta get atomic again. In phosphorescence, you can excite the atom again with maybe an ultraviolet photon and it jumps up a few levels. But it gets stuck there. Quantum mechanics allows it to get stuck. It's not allowed. This atom, the coyote is hanging there over the Grand Canyon but he's not allowed to fall down. Quantum mechanics says, no, it takes something to disturb this atom. It's sort of like if you had a hill. This will be a normal atom, if you dropped a ball on top of that hill, it would roll down immediately. It can't stay up excited, high energy state. If you had a hill that looked like this, however, and you dropped the ball on top of that, there's no way for that ball to roll down the hill. It has to be disturbed somehow and then it will roll down the hill. Same thing in phosphorescence. That disturbance can be another atom bumping into it, heat or light shining on or something. But eventually that atom will get bumped into and it might then give off some energy, maybe a red photon. But it can jump down again so that it would give off then maybe a green. So phosphorescence hangs onto its energy, it's kind of greedy and hangs onto its energy unless it's disturbed into giving up that energy. I'll show you some phosphorescent stuff. That stuff that we have on the wall of the shadow box. Let's turn the lights down 'cause I'm gonna need the lights all the way down before I can do this. There we go. That phosphorescent material was made with this powder. This powder glows after, I know this looks like something from a science fiction movie that you shouldn't get near, but this is just the phosphorescent chemical that holds onto the energy. And they put this pigment into various things like those stars or into this, it's here, it's in a piece of vinyl right here. So if I shine my light on this thing, it's glowing. And if I take my hand away, my shadow is still there but this is phosphorescent. By the way, you know that you, I don't know if my hand is warm enough to do this, but you can increase the rate at which the atoms bump into each other by heating it up. Let me see if I can do that. If I go here and I breathe on it. Do I get a bright spot in the middle? Yeah, so that is because that I'm causing them to be hotter and they're jiggling around faster and bumping into each other more often. Here's another material. This material has a different phosphor so this glows in slightly different color, it's kind of a cyan glow. Actually, cool thing you can do is you can take a laser and you can shine, this is kind of an ultraviolet laser. And you can draw on the vinyl then. It's kind of fun thing to do, isn't it? Or here I can do, whoo! My favorite substance is this stuff right here, I know it's kind of hard for you to see it right now but this is phosphorescent formica. You know the stuff they put on top of kitchen tables? This is phosphorescent formica. So you could actually do your kitchen now in phosphorescent formica. Your cabinets in your kitchen, your kitchen table, your kitchen counters, and you go in at night, it's gonna glow. So getting your midnight snack will be much easier. And this phosphor does come in lots of different colors. This is just a bunch of those phosphors and you can see that it's glow, oh, and let me use the ultraviolet light. Where did my ultraviolet, there it is. Lose everything in the dark here. These are different phosphors and they glow in different colors so you can... Just like the fluorescent things, you can also get phosphoresce in things that are different colors. The most efficient one is this green color. The rest of them are quite as efficient but they do come in different colors. Oh, one cool phosphorescent thing I wanted to show you, Skippy. Did you know that peanut butter is phosphorescent? I'll bet you didn't. Yeah, I saw it on YouTube. Let me get my laser. Okay, so let's turn the lights down again. Okay, here we go. Right, I'm gonna draw on the Skippy. It's not very phosphorous and it's not very efficient but it is, your peanut butter can glow in the dark. And no, I didn't mix any of that powder into this. This is a giant jar of Costco Skippy. One last thing I wanna mention is these, let's turn on my projector, there we go. These right here, what you're looking at here are quantum dots. This thing right here, I can show this. You don't even have to turn the lights out for this. You can see these without the lights out. Quantum dots. Inside of these little vials are little tiny particles. The chemicals in each one of these vials is exactly the same. The only thing that changes is the size of the particle. By changing the size of the particle, you can change the color that it fluoresces at. And here you can see that if ultraviolet or blue light comes in, that particle fluoresces in different colors depending on the size of the particle. And you can see here, the size of the particles change from two nanometers, billions of a meter in diameter to six nanometers, six billions of a meter in diameter. Six billion, yeah, six billionths of a meter. That's pretty small. You can imagine that to get these things, to manufacture these things, you have to manufacture the little tiny particles inside of here at all the same size to get them to all glow the same color. This is a challenge in manufacturing, but which they have of course conquered by now. And these are being used in television sets as a light source behind your LCD television, has a light source in the back. It has an LCD in the middle and the LCD can only turn the light source on and off. It's white or it's not white. And then in front of that in front of those dots, they put colored filters, red, green, and blue colored filters. So they can turn on and off, red, green, and blue things. But if you could make the source of light behind match the red, green, and blue colors of the filters which you can do by using quantum dots, you can make your TV much more efficient and you get much more color range and saturation of colors. So these quantum dot TVs, which are being made by lots of different manufacturers, the specific one is Samsung. And I'm not advertising Samsung televisions, but they do make a quantum dot television. What an amazing thing to do? And that's unfortunately all I have time for tonight, 'cause I'm already over time. So thank you for coming. If you wanna come up and check any of this stuff out, come on up and enjoy the rest of your night here at the Exploratorium. Thank you.