I’ve got some glow in the dark toys that are at least 20 years old and they still glow. What kind of chemicals do they use to make Glow in the Dark items? How does it work? How can the effect last so long?
While compounds containing phosphorous were the origin of the name, they work in a different way than just “store energy and release it later”. Yet Another Terminological Mixup.
Probably Strontium aluminate, I am not sure how to describe how phosphorescence works here without the math.
Basically exposure to light kicks an electron to a higher energy state and it takes a while for it to re-admit a photon and fall to the original energy state. Not exactly correct analogy but maybe it will help?
Hopefully someone who knows how to will provide a better explanation.
Strontium aluminate’s only been used in glow in the dark toys for a few years. Before then they used copper-activated zinc sulfide/copper-doped zinc sulfide.
To be clear, there are two different sorts of glow-in-the-dark things. Some things absorb energy from ambient light, and then glow for perhaps an hour after you turn the lights off, by releasing that stored energy. The precise details of how the energy is captured, stored, and released might vary, but the net result is that they don’t glow for very long.
But it sounds like the OP is referring to things that just keep on glowing, continually, no matter whether or how much external light they’re exposed to, and which have been doing so for decades. This is also possible, but it’s powered by nuclear decay. Nowadays, anything that does this uses tritium, which has a half-life of about 20 years, so if that’s what the OP has, they should still be visible, but noticeably faded. But they used to do it with radium, which has a much longer half-life, and would not be noticeably any dimmer now than it was when brand new.
If you’re worried about safety, radium is an alpha source. That means that it’s completely safe, as long as it’s outside of you: Even ordinary skin is good enough for shielding against alpha particles. But on the other hand, you absolutely do not want to ingest (eat, inhale, get embedded in a wound, etc.) an alpha source, because they’re the most damaging sort of radiation to have inside of you.
As an aside, today I saw some bags of glow-in-the-dark Kit Kats at a surplus store (leftovers from Halloween, but new to me.) Some googling showed that it was just the wrappers that were gitd, and they hadn’t found some food-grade way of doing it.
I think you are mis-interpreting the OP.
“They still glow” means that if you take them into a dark room, they glow. Not that they glow forever when kept in the dark.
Radium hasn’t been used in decades, and tritium was way too expensive for toys.
He said that they were “at least 20 years old”. That encompasses the possibility that they’re much older, possibly old enough to be radium. And surprise at “the effect lasting so long” sounds odd to me, if he just means that they still glow for a little while after you turn off the lights, like they did when they were new.
Well, I can’t find any examples of GITD toys made with radium, so there’s that data point…
If by “A few years” you mean ~24 years.
The blue version came out in the early 2000’s but note that the brightness increase was the huge change from that 1995 patent and related 1996 paper.
And from 1968 with links to patents from 1961 Philips Res. Repts 23, 201-206,1968
Note, while I don’t know if it was used in toys at the time of this 1968 papers calls out:
The method was known,
Doping with Dy[sup]3+[/sup] is what was novel in the mid 1990’s and which added to the brightness and time and then 5 years latter blue and red with other forms.
http://jes.ecsdl.org/content/143/8/2670.abstract
SrAl2O4:Eu2+and the sulphide based phosphors were both in use before they started doping with Dy[sup]3 +[/sup] in the mid 1990’s. As sulphide based phosphors absorb moisture from the air to produce sulphates which no longer glow or at least are very dim they probably aren’t the ones in use.
I do see where some searches claim that it has only been used for a few years, but it seems that verbiage has been cut and paste around the internet for about 20 years. Here is another patent in increased brightness from China in 1991 talking about toy applications.
I should note that LumiBrite, LumiNova, and Super-LumiNova that was almost universal on watches in by the late 90’s is directly related to that Neomoto patent I provided above. While Strontium aluminate had existed before, doping with Dy[sup]3+[/sup] is what allowed for several hours of glow.
Replacing Tritium lumed dials was the first application in 1993 it looks like but then usage exploded over the next couple of years.
I was at a plane graveyard a long time ago. Inside of an old passenger liner I noticed the “exit” sign was on. I popped It off and it still glowed. I have it in storage somewhere but last time I saw it it was still glowing.
Any radium may still be crazy radioactive, but would the phosphor still be good after 20+ years? One can always test the toys using a Geiger counter.
I don’t have a cite but even 20 or more years ago I recall seeing trivia about how glow in the dark watches were made with radium in the early 1900’s and how the practice had been banned for decades. Although there was a silly retro comic that supposedly took place in the 50’s where the hero got his powers from being exposed to his radioactive glow in the dark toys.:rolleyes:
Well, since you are back, can you clarify? Do the toys you found require “charging” by exposure to light, or do they glow all by themselves?
What is the half-life of all these enhanced-brightness phosphors ?
(I’ve got CFD’s with almost no remanence, long tubes that glow faintly for seconds, my watch that’s good for half an hour, and my brothers watch that is good for one night.)
What’s a “CFD?”
They’re dark until after they’re exposed to some light source. I’d definitely be worried if they glowed all the time, especially after 20 years.:eek:
[Flies off into the sunset]
So the link I gave in the 2nd post is the right one. I’m sure you have no problem with the following quote: 
"In the special case of phosphorescence, the electron which absorbed the photon (energy) undergoes an unusual intersystem crossing into an energy state of higher spin multiplicity (see term symbol), usually a triplet state. As a result, the excited electron can become trapped in the triplet state with only “forbidden” transitions available to return to the lower energy singlet state. These transitions, although “forbidden”, will still occur in quantum mechanics but are kinetically unfavored and thus progress at significantly slower time scales. "
A photon “charges” an atom in a phosphorescence molecule by putting an electron in a higher energy state. The electron wants to lose the energy by emitting a photon back out. Most materials do this right away. But for certain materials the “easy” route is sort of blocked. However, these are atoms and quantum stuff happens. At random times the electron can make the crossing to the lower energy state, giving off a photon in the process. The energy of the emitted photon and the material the atom is embedded in affects the color of the photon given off.
For usable materials, the higher energy state has more than just a higher electron orbit. Hence the “spin” state of the electron is mentioned.
These materials can last a long time depending on the material it’s embedded in, temperature it’s stored in, how well it’s made, etc.