You can bring real glowing stars home
Glow-in-the-dark stars are a very popular decorative choice for children's rooms because they combine attractive design with an intriguing and calming glow after dark. The glow is the result of a complicated physical process called phosphorescence. Phosphorescence occurs when a material absorbs light in the form of photons from an external light source, and then "stores" that light energy until the light source is removed, allowing it to glow in the dark.
Calming Stars
Glow-in-the-dark stars are a popular edition to children's walls and ceilings, giving off a faint luminous glow that helps calm and soothe children as they drift off to sleep.
A Host Of Glows
The glow in glow in the dark stars is the result of phosphorescence, a kind of photoluminescence. Photoluminescence is a kind of glow generated by materials that absorb photons (discreet packets of light energy) from a light source, and then emit them back into the world. In many cases, this happens immediately, or almost immediately, though it's important to distinguish immediate photoluminescence from other forms of light generation that produce "glows". Glow sticks, for instance, work by chemiluminescence, which is a chemical reaction that emits light immediately and in all conditions.
Glow Prisons
Phosphorescence though is completely, and very noticeably, different from chemiluminescence. In phosphorescence, the material captures or absorbs its photons from an ordinary light source, and then stores them for some time before it emits them again. In essence, phosphorescent materials act as "glow prisons", which continue to release their light when the original light source is no longer available.
Forbidden Energy States
The explanation for why some materials are phosphorescent, and others are not, is very complicated--so complicated it takes quantum physics to really explain it. However, most people who make use of phosphorescent materials don't need to dig out their quantum physics textbooks, and read up about forbidden energy states, triplet phases and multiplicity energy spin. For most modern applications, it is enough to know that phosphorescent materials trap light in the form of protons, and release it slowly when the light source is removed.
Pigmentation Power
In the case of glow in the dark stars, as well as a range of other things, including safety signs in public buildings, the secret to the glow is in the pigment in which they are coated. The pigment is made up of tiny, crystalline rocks in suspension, as a kind of paint. The shape of these minuscule rocks acts to trap the photons and store them. Because the glow is in the pigment, practically anything can be made to glow--you simply cut the shape you want, and coat it in the crystalline pigment.
Charging Stars
The way the crystalline rocks store photons, incidentally, is why in most cases, glow in the dark stars come with instructions that ask you to put them under a direct light source for some hours before using them. That is enough to "charge" the stars with photons.
Then, when conditions change, and the outside light goes down or is turned off, the tiny "glow prisons" in the pigment continue to release their photons, giving off the familiar glow.
Glow-in-the-dark stars are a familiar, friendly application of quantum physics in your child's bedroom.
The Mind-Boggling Bit
For those who really want to understand the quantum physics involved in phosphorescence, it works like this: the molecules in phosphorescent materials, when subjected to a light source, absorb photons and change their state, from a "ground state" to an "excited singlet state"--having extra photons changes what they are and how they behave. Some molecules then go further, and achieve what's called a "triplet stage", in which they are "stuck" for some time, unable to immediately re-emit the photons they absorbed. These molecules decay over time, going back to their original "ground state" by emitting photons, and it's these emitted photons that cause the glow.
Tags: light source, , phosphorescent materials, quantum physics,