Tenebrescent Potassium Iodide

[alan sailer]

I was browsing through an element sales catalog and ran across a cute science demonstration.

The site sold a small ampule with powdered potassium iodide sealed under vacuum. The claim was that the KI
when bombarded using a tesla coil will change color. I have all the needed material so I gave it a try. And it's true.

The phenomenon is called tenebrescence. I knew of it from a friend who collects fluorescent mineral. One, called hakmanite
turns purple under shortwave UV and reverts to white in sunlight or LW UV. The high energy SW UV excites
electrons into a new stable state creating a color or farbe center, f-center for short.

In addition to creating a neat color change the powdered KI creates a tiny fractal "crackle" effect seen in commercial
plasma displays.

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The tesla coil is a small CW unit that runs on antenna feedback. One mystery is that the element website says that the KI turns
orange and my sample turns purple.

Cheers.

[haversin]

I didn't see the color change did you show it?

[alan sailer]

No I didn't. If you want I can take a before and after picture and show it. The color change can't been seen as it is happening
because the "lightening" is too bright.

Cheers.

[haversin]

If you took a video of the KI in the low energy state "bleached" with room lights on and then turned on the tesla coil leaving the room lights on maybe you could see the color change. Then turning off the tesla coil the color decay could maybe be seen. I've seen this done with mineral demos of tenebrescence but they usually turn off the room lights during the short wave UV activation to show the fluorescence.

[alan sailer]

Yes.

I did some photo tests and I'm afraid showing the effect in video would be challenging. The color change
is not as dramatic as some hackmanite I've seem that goes from dark purple to almost white. The best purple
I can get from the powdered sample (under vacuum) is more of a light lavender. It's clearly visible in person
but in photos not so much.

I could cheat and over-saturate the pictures but will not.

I'm also wondering if the process of activating the powder coil is also destroying the tenebrescence as fast
as it is creating it. The darn tube gets really hot really fast.

Cheers.