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Conundrum

Wed Sept 08 2010, 05:20PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.

Do any of these look like they can be repurposed for EL use?

the TiO2 paint *might* be useable mixed with BaCO3 then heated to form BaTiO3 (the required dielectric) and the zinc sulphide in the paint could possibly luminesce with the trace impurities present if rinsed and dried.

-A

Adam Munich

Wed Sept 08 2010, 07:52PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
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That's zinc oxide, not zinc sulfide.

radiotech

Fri Sept 10 2010, 03:48PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Here's a bottle of luminous Ca Sulphide that does glow by itself and gets charged when illuminated by UV or regulart light. Never did know how they seperated luminous calcium sulphide from just plain old calcium sulphide. (maybe just this batch glows?) Also some Uranyl Zink Acetate. Those 3" EL panels are available for a dollar too. I'm thinking that glowers might be detected by making a very dark box and sticking a photomultiplier tube inside and looking at the signal for a while to see if a feeble glow exixts, then see what zaps it up. Is there a magnetoluminescent material?

Somewhere there is a paper on ghosting in PM tubes that is they give a signal after the main signal is over. There may be some effect like that in EL panels too, though at very low level.

Conundrum

Fri Sept 10 2010, 07:54PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

interestingly BaS also glows, though it is fairly toxic.

many relatively mundane substances such as rare earth
oxides can be used as dopants from what I have read..

just received 10 metres of clear heatshrink, so am experimenting with my white EL wire to make multicolour "bundles" with a possibility of using conductive thread to address the wire and make it light at one point depending on the relative phasing of the applied signal at each end of the thread.
made up one "module", not tested it apart from to confirm that it glows nicely.

another hack (inspired by Jeri's work with homemade EL) is to mix blue EL with green GITD strontium aluminate to make it luminesce for longer periods between flashes, not done yet...

EDIT: for those who wish to duplicate this, DO NOT remove the inner "heatshrink" or the EL will go patchy on you no matter how much wire you wrap around it.
Interestingly thread reduces this problem at least on the white EL wire.. go figure.

I tried the ZnS:BaSO4 paint on a convenient piece of ITO glass but it didn't glow. It did however exhibit a sort of pseudo-capacitor effect which is noteworthy as a 1cm2 section exhibited a capacitance of nearly 10uF with about a 100K resistance from silver paint to ITO.
next step is to try homemade barium titanate with different phosphors..

regards, -A

Proud Mary

Fri Sept 10 2010, 11:26PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radiotech wrote ...

Never did know how they seperated luminous calcium sulphide from just plain old calcium sulphide.

Phosphors and scintillators are usually prepared by prolonged 'activation' at high temperatures - often 1000 C or more - for hours on end, milled down into a powder, re-heated for more hours, and so on.

Dopants cannot be added to a phosphor as an afterthought, but have to be introduced into the lattice from the outset, but of course where there are existing impurities these may actvate a phosphor, while the completely pure material may have no activity at all.

Secondary dopants may serve to make a glow persist, or conversely, cut it short, as is usually desired in high speed counting, or X-radiography, where 'afterglow' in the intensifying screen will ruin the photographic image inside the cassette.

Adam Munich

Sat Sept 11 2010, 01:47PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I wonder if it would be possible to activate the phosphor by melting it and introducing silver. Of course, reaching 2525 Â°C is no walk in the park, but with a homemade arc furnace it could be done...

Conundrum

Sat Sept 11 2010, 02:51PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

hmm.. homemade arc furnace isn't that difficult.
i wonder if i could use a microwave absorber such as ferrite, to superheat the powder with an infrared thermometer to feed back current temperature to keep it at 1000C?

EDIT:- I have one of the Sparkfun IR thermometer modules, has anyone here used one?
i'd really appreciate some pointers...

-A

Pinky's Brain

Mon Oct 18 2010, 07:08PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Would UV phosphors work for EL or is the effect fundamentally different?

How about high energy electron bombardment? (Barrier discharge, ie. putting a spark through it.)

IntraWinding

Mon Oct 18 2010, 10:13PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

If you need some Titanium Dioxide I can send you some.

Conundrum

Tue Oct 19 2010, 07:40PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Pinky's Brain wrote ...

Would UV phosphors work for EL or is the effect fundamentally different?

How about high energy electron bombardment? (Barrier discharge, ie. putting a spark through it.)

Might work, Jeri has just published a Youtube video on how to convert ZnS glow powder into EL phosphor.
iirc she used a kiln but it ought to work with more direct heating.

a little tip, parallel connected CCFL inverters can be repurposed into a makeshift arc furnace...

-A

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