Red LED light makes GITD "un-glow"

[Silviron]

Maybe this is old news, since I haven't followed the glow threads very much(did do search, didn't find anything about this).

Anyway, I have a braid of that cheap GITD plastic lace (or whatever you call it) around the lampshade next to my bed-

Last night I was playing around with my newest mod which uses a red/orange Lambertian LS LED- I shined the light directly on the GITD braid- and in every spot I shined it for just a few seconds, the glow actually went away completely!!

OK, even I know that UV light is the best to charge GITD stuff, but I was completely amazed that bright red/orange light has a completely NEGATIVE effect on it.

I realize that the red/orange is at the opposite end of the spectrum from UV, and wouldn't have been surprised if it had had just a minimal charging effect, or even NO effect, but a subtractive effect???

 

[Wingerr]

Maybe it just looks that way because your eye adapted to the bright light, making everything appear dimmer.
Do it seem to do the same thing if you shut your eyes while lighting it up?

 

[Empath]

This is a very significant question. If I can find my cheap NeoGlo orange LED light, I'll check it out against a fully charge Alien Skin sheet. I'm trying to picture how a certain part of the light spectrum would rob the energy. If it does so, the energy has to transfer into something else. Good question, Silviron.

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by wingerr:
[QB]Maybe it just looks that way because your eye adapted to the bright light, making everything appear dimmer.....
[QB]<HR></BLOCKQUOTE>

No, that isn't it-

I put the head of the light right on the braid, and after a few moments turned it off. Where the LED light was not in contact, the braid still glowed as brightly as this cheap stuff normally does. Where the light was, I could see no glow at all.

I will accept that if my eyes were completely dark adapted I might have ben able to see some glow in the dark spots, but the LED light did have a definite and significant subtractive effect.

I then shined a turquoise LED light in contact with one of the darkened spots for a moment, and it "recharged" and glowed brighter than the rest of the braid. (as one would expect).

 

[Empath]

I tried both red and orange on Alien Skin. Neither of those created that effect. If you come up with anything else, be sure to post it. The loss of energy is puzzling.

 

[Silviron]

Since that Alien Skin is the high power stuff, and uses (I believe) a different chemistry, maybe it just doesn't have the same effect.

Try it on some of the cheap, older formula stuff. I don't have any other GITD material around here- just the lace that I bought in the craft department at Wal-Mart for about 49 cents.

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Silviron:
I realize that the red/orange is at the opposite end of the spectrum from UV, and wouldn't have been surprised if it had had just a minimal charging effect, or even NO effect, but a subtractive effect???<HR></BLOCKQUOTE>

The physical effect is known as "phosphorescence quenching".

This presumably occurs because the red light is sufficient to excite electrons out of the metastable state in ZnS (zinc sulfide) and into a state from which they promptly decay into the valence band. Once the electrons have returned to the stable valence band, you can no longer coax any light out of them until you bump them into the outer shells again with a blast of blue or UV.

The majority of commonly available glow-in-the-dark items that rely on copper-doped zinc sulfide to provide the phosphorescence will show this effect; strontium based materials are more resistant though not totally immune.

Here is a short article I found about this. It's a bit on the technical side.

At least three energy levels are involved. An electron is excited from the ground state to the top level, and from there it decays to the middle level. Because transitions from the middle level to the ground state are forbidden, the electrons get "stuck" in the middle (metastable) energy level. Eventually they do decay back to the ground state, giving up light (the phosphorescent glow) in the process. One can note that the yellow-green color of the phosphorescent glow corresponds to a longer wavelength than the blue light needed to excite the glow. The reason why red light quenches the glow is presumably because the red light is sufficient to excite electrons from the middle metastable state to a slightly higher state, from which the electrons decay promptly. Although the previous explanation is sufficient to convey the general idea, it begs the question of why the electrons get "stuck" in the first place. There is a vast body of literature on ZnS phosphorescence, and the answer to this question is complicated because ZnS is a semiconductor . Traditional explanation of phosphorescence address atoms with metastable states. However, this explanation is not accurate for ZnS phosphorescence which involves the movement of both electrons and holes. ZnS is a semiconductor with a band gap of 3.6 eV between the normally full valence band and the normally empty conduction band. Doping the ZnS with copper provides additional sites for electrons to reside at an "energy level" within the band gap. Illuminating the ZnS with light of sufficient energy excites valence band electrons to the normally empty conduction band by several routes. The holes in the valence band are filled with electrons obtained from the copper sites. Emission from the conduction band to the intermediate-energy copper site cannot proceed until a hole at a copper site becomes available. Electrons from the copper site cannot readily drop down into the valence band, which is normally full. When conduction band electrons finally do combine with the holes at the copper sites, the ZnS glows with light with a peak wavelength of 540 nm.

 

[Silviron]

Cool, Craig, Thanks for proving I'm not insane.....


Well, about this particular subject anyway

 

[Empath]

Thanks, Craig. It sounds like you're trying to say the red light shakes the little rascals out of the branches all at once, instead of letting them drop on their own as their little electron arms give out.

 

[The_LED_Museum]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Empath:
Thanks, Craig. It sounds like you're trying to say the red light shakes the little rascals out of the branches all at once, instead of letting them drop on their own as their little electron arms give out.

<HR></BLOCKQUOTE>

I couldn't have said it better myself. Perfect analogy.

 

[Wingerr]

Neat stuff! I'll have to go try it out; certainly not something you'd expect-

 

[Andre2002]

Sam Goldwasser has this one on his Laser FAQ , IIRC .

And it works better with a red laser pointer

-Andre

 

[krept]

very cool info

 

[Slick]

Here's something else that's interesting..

I decided to try this test using a plastic glow-in-the-dark "ceiling star". The red/orange LS was placed directly against the plastic and powered on. After removing the flashlight, there was a "black hole" where the beam knocked out the glow. BUT the area around the "black hole" was actually glowing BRIGHTER than the rest of the plastic... To me, that pretty much proves the "electron drop" accelleration theory.