# Phosphorescence **URL:** \ **Category:** Factual Questions\ **Created:** [December 20, 2000, 3:48am UTC](https://boards.straightdope.com/t/phosphorescence/46466 "2000-12-20T03:48:37Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 20, 2000, 3:48am UTC](https://boards.straightdope.com/t/phosphorescence/46466/1 "2000-12-20T03:48:37Z")
After lights-out tonight, my daughter was admiring the “glow in the dark” stars on her bedroom walls and asked me how they worked. I told her that certain chemicals in the stars had been absorbing some of the light in her bedroom and were now giving it back out. She was happy with this explanation, but I sure wasn’t. Am I right in viewing phosphorescence as _analogous_ to emission by an excited electron as it falls back to a lower energy state within an atom? If so, what in phosphorescence corresponds to the excited state? Where and how is the incoming light energy stored until it is re-emitted as ‘day-glo’? Thanks. ---
**Author:** ![Myrr21](https://avatars.discourse-cdn.com/v4/letter/m/e495f1/32.png) [@Myrr21](https://boards.straightdope.com/u/Myrr21)\ **Post date:** [December 20, 2000, 4:30am UTC](https://boards.straightdope.com/t/phosphorescence/46466/2 "2000-12-20T04:30:21Z")
Well, here we go. To understand it requires some background info on fluorensence–which basically occurse when light is absorbed (the molecules shift to an excited electronic state), and then re-emitted. Basically, think of a blacklight. Of course, when the light goes away, the glow stops almost instantly too. Here’s where phosphorescence comes from. If there’s an excited state–lower than the one you excited the molecules to originally–which “crosses” (I can be more specific if you want) the original one, the molecules will drop to that state before dropping down to the ground state. This, however, is a semi-allowed transition, so it doesn’t just happen instantly to all the molecules–hence, the continued glow once the light source is removed. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 20, 2000, 4:42am UTC](https://boards.straightdope.com/t/phosphorescence/46466/3 "2000-12-20T04:42:05Z")
**Myrr21** : You lost me there. Right after you said, “here we go”. Are you saying there is an intermediate (semi)-stable state of the excited molecule? Sort of in a dip in its energy curve? ---
**Author:** ![Bob\_Scene](https://avatars.discourse-cdn.com/v4/letter/b/e19adc/32.png) [@Bob\_Scene](https://boards.straightdope.com/u/Bob_Scene)\ **Post date:** [December 20, 2000, 4:44am UTC](https://boards.straightdope.com/t/phosphorescence/46466/4 "2000-12-20T04:44:14Z")
In case you’re interested, the chemical that makes most glow-in-the-dark toys work is zinc sulfide. ---
**Author:** ![Myrr21](https://avatars.discourse-cdn.com/v4/letter/m/e495f1/32.png) [@Myrr21](https://boards.straightdope.com/u/Myrr21)\ **Post date:** [December 20, 2000, 4:57am UTC](https://boards.straightdope.com/t/phosphorescence/46466/5 "2000-12-20T04:57:41Z")
Sorta. The idea is that there’s an intermediate state that you don’t get to in the intial excitation–it skip over that for reason you probably don’t care about. However, it is available from the excited state, so instead of going straight down to the ground state (fluorescence), it sorta makes a “detour” into the intermediate, then drops back down to ground (phosphorescence–which takse some time). ---
**Author:** ![Dr.Lao](https://avatars.discourse-cdn.com/v4/letter/d/2bfe46/32.png) [@Dr.Lao](https://boards.straightdope.com/u/Dr.Lao)\ **Post date:** [December 20, 2000, 5:45am UTC](https://boards.straightdope.com/t/phosphorescence/46466/6 "2000-12-20T05:45:55Z")
I love the way my physical chemistry book descibes the emmission step in phosphorescence. It calls the step “approximately” forbidden. So when a physical chemist says something is forbidden, you got to ask him how forbidden it is. 😃 Anyway, **Myrr21** has been correct in his description, but if you want more details here are some websites. [http://www.shu.ac.uk/schools/sci/chem/tutorials/molspec/lumin1.htm](http://www.shu.ac.uk/schools/sci/chem/tutorials/molspec/lumin1.htm) [http://www.shsu.edu/~chemistry/chemiluminescence/JABLONSKI.html](http://www.shsu.edu/~chemistry/chemiluminescence/JABLONSKI.html) ---
**Author:** ![Andy](https://avatars.discourse-cdn.com/v4/letter/a/aeb1de/32.png) [@Andy](https://boards.straightdope.com/u/Andy)\ **Post date:** [December 20, 2000, 11:50am UTC](https://boards.straightdope.com/t/phosphorescence/46466/7 "2000-12-20T11:50:22Z")
If anyone is _really really_ interested in this topic, you could quit this board and get on over to [The Society of Fluorescence Message Board](http://www.insidetheweb.com/messageboard/mbs.cgi/mb18331). Have a wild time.