a while ago I tried to charge a glow-in-the-dark sticker using a simple red laser pointer. It was a large sticker, of the type used to mark emergency exits and fire extinguishers here in Germany. I thought I could draw a picture this way, with glowing strokes.

To my surprise, the exact opposite happened - the sticker was already glowing a little bit and the areas I illuminated with my laser turned dark instantly, as if the charge of the sticker was removed by the laserlight.

The effect was reversible, the darkened areas would charge and glow as usual if exposed to normal light.

So I was able to draw a picture after all - however, it was a negative.

Can anyone explain why the sticker was discharged instead of charged by the laserlight?

How interesting. 

Presumably the "glow-in-the-dark" effect comes from the decay of a meta-stable excited state. It gets charged by sufficiently energetic photons, and decays slowly because some selection rule prevents a direct transition without an external influence.

If this is the case, we can guess that the laser is exciting the meta-stable state to a still higher energy state which is not subject to the selection rule so that it promptly falls to the ground state1, from which the low energy photons in the laser don't have the energy to push back into the meta-stable state. 

I think I'll try to make a demo out of that. Thanks.



1 Presumably you could see the light of this decay if you filtered out the intense red from the laser. Try a green or blue filter. Or a spectrograph.
