why do things glow in the dark
Are you afraid of the dark? It's OK to be a bit scared of things that go bump in the night. But what about things that glow at night? You've probably seen or played with glow-in-the-dark toys before. From yo-yos and balls to stickers and stars, glow-in-the-dark toys can turn any dark room into a magical world of adventure! Have you ever WONDERed how these things glow in the dark? Guess what? It's not magic! It's just plain and simple science. Glowing in the dark Б also known as Б simply requires chemicals that store energy when exposed to light. These special substances are called. This type of glowing is sometimes called. visible light after being. This means you have to expose the items to light for a while before they will glow in the dark. then slowly release their stored energy over time. As they release the energy, they emit small amounts of light, which we see as an object glowing. Sometimes glow-in-the-dark objects will only glow very weakly for a short time. Often, you have to place them in a very dark place to see their faint green glow. Newer glow-in-the-dark items may glow more brightly for several hours. Over the years, chemists have created thousands of chemical compounds that act as. For glow-in-the-dark toys, manufacturers look for
that can be by normal light and that glow as long as possible. To make glow-in-the-dark toys, manufacturers mix their chosen phosphor into plastic and then mold it to the desired shape.
Two of the most common found in are and. There are a couple of other types of. , for example, makes object glow in the dark because of a chemical reaction. When two particular chemicals react, they produce energy that is subsequently released, creating a glow. This is what happens in. uses that are constantly charged by adding a radioactive element, such as radium, to them. You may have seen this type of on the hands of a watch, for example. One final example from nature is. Some creatures, such as fireflies and, contain chemicals within them that cause them to glow. Some of these creatures glow for protection, or to attract mates. Toddlers and young childrenВ are often fascinated by anything that glows. The moment they see something shiny or bright, chances are good that it will end up in their mouths in the next moment. In fact, not just kids, but a lot of adults also canвt resist looking at an object that glows in the dark on its own, without the help of any power or electricity. There was a time when wristwatches with luminescent dials were a major fashion fad amongst young people. The question is,В how did the dial radiate light? Some people mistakenly assume that the cells that power the watch also make the dial glow continuously at night. In this article, we are going to take a closer look atв How do glow-in-the-dark objects work?
Short answer: Things that glow in the dark contain a substance called phosphor, which is capable of radiating light after it has become energized. Such substances first soak up energy for long periods when exposed to light and subsequently radiate visible light in the dark. Before we get into the details of this phenomenon, it helps if we understand a few of the basics first. What is luminescence? Luminescence is the emission of light by materials that are relatively cool. This is different from the light emitted from incandescent materials, such as burning charcoal, wood, paper etc. , as the light in those cases results from heat. Since the emission of light is done by relatively cooler materials, luminescence is also called cold-body radiation. Contrary to what many people believe, the luminescence of an object doesnвt just mean that it вglows in the darkв; rather, any object that gives off light it produces itself is said to be luminous. Materials that glow in the dark (all by themselves) are just some of the many materials that demonstrate luminescence, and are therefore sometimes called luminescent materials. Luminescence comes inВ a few types, including phosphorescence, fluorescence, bioluminescence, chemiluminescence, photoluminescence and various others. For the scope of this article, we re only interested in the first two.
All materials that glow in the dark contain substances called phosphors. In the simplest terms, a phosphor is something that exhibits luminescence. There are hundreds upon hundreds of compounds that can act as a phosphor, including those that are used in glow-in-the-dark toys and radar screens (e. g. ,В zinc sulfide, strontium aluminate etc. ), as well as В the ones they use in computer screens, white LEDs and sensors. The large number of phosphors could be categorized based on three main parameters: the type of radiation they require to get energized, the color of their output light and how long they glow after being energized. In the case of вglow-in-the-darkв toys, you need phosphors that get energized by natural (visible) light and glow for a long time after being energized (high persistence time). The two compounds that fit these criteria perfectly, much to the delight of toy manufacturers, are strontium aluminate and zinc sulfide. There are a number of other compounds that do this as well (e. g. , calcium sulfide with strontium sulfide activated by bismuth). How does phosphorescence work? Phosphorescence is a special type of photoluminescence (quite similar to fluorescence), where phosphorescent materials produce light after being energized. When the atoms inside these materials gain energy (through visible light or other sources), they become вexcitedв.
When these atoms return to their normal energy levels, they emit tiny packets of light called photons, which make the object (that contains these atoms) shine. Luminous wristwatches work on the same principle. They charge up with energy during the day and start glowing once it s dark (when the photons are emitted as вexcitedв, atoms lose energy). How do вradiumв wristwatches glow in the dark? In the past, there were wristwatches, popularly called вradium wristwatchesв, thatВ glowed but did not need any charging. Such watches rely on radioluminescence, wherein a phosphor is mixed with a radioactive element. The radioactive emissions from the material (in this case, radium) energize the phosphor continuously, making it glow all the time without requiring any charging. Radium wristwatches have largely been discontinued now, and have since been replaced byВ variants that either contain a man-made radioactive chemical element called promethium, or a radioactive isotope of hydrogen called tritium. So, the next time a kid asks you why their toy glows when the roomвs lights are switched off, you might want to tell them about the real story behind it all. Or, you can skip theВ details and let them believe that the toy is illuminated by a fairy named Science. Luminescence Phosphor Radioluminescence Phosphorescence Luminescence Phenomena
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