math
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"Coating" of phosphors (glow in the dark powders) for water compatibility?
Hello,
sorry if I'm asking yet another question coming from my question-filled mind.
I understand there are certain compounds called phosphors like strontium aluminate which are doped with a rare earth metal (I think by mixing some in
equal amount across the powder particles?) and that are then used in apolar solvents (or more properly carriers, since I doubt they dissolve the salt
or the doping?) and used in many applications.
I however saw recently a glowing powder (still strontium aluminate) which is advertised as coated for water compatibility.
I don't clearly understand what does this mean and how it's done.
For example, what does it happen when Eu-doped strontium aluminate is put in water? Does it dissolve and no longer exhibit the glowing when no light
is applied? Or does it last only until it's crystallized back to dryness?
Also what does it happen when a phosphor powder is put in paints?
I tried to search phosphor coating water on google but found only advanced electronic stuff related to LED, which I think uses a different physical
phenomenon.
Probably somebody of you own or has read a copy of Phosphors Handbook which given its title may contain an answer?
My idea was to make a glowing paint using paint and this powder, however given that it's not coated for water, I think that it's not waterproof and
would lose its glowing effect with rain.
Would it glow if mixed with a colored paint or would it need to be put in transparent paint or again sprinkled on top of fresh paint? If not, would I
have to put cyanoacrylate glue on the dry paint and then apply glowing powder or maybe apply a layer of transparent paint to waterproof the whole
thing?
Thank you
[Edited on 9-7-2013 by math]
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Acidum
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"Coated for water compatibility" - imagine very fine bead-like particles of your phosphor, that are coated with thin layer of material that doesn't
dissolve in water, most likely some polymer.
If you have some mixture with specific properties depending on composition (strontium aluminate doped with europium), by putting it in medium that
will alter its composition you will render its properties completely different. Most likely, phosphor components will dissolve or disperse, and lose
its properties. By evaporating or crystalizing it, fine composition may be different, and properties may still be lost.
Materials doped with something generally work like this - you have fine particulate, or even atoms or molecules, of basic material (basic as in
primary, not as in alkaline), and for every x atoms/molecules/particles of base material you have 1 particulate of dope material, which is in contact
with all surrounding base particles.
So by evaporating or crystalizing solution/dispersion you might not get primary mixture, because:
a) base and doping materials might separate (separate layers or crystals)
b) particle size of material might not be adequate
...of course, it could work perfectly, but very rarely...
As for paint, my best guess would be surface layer of coated phosphor dispersed in transparent carrier, painted over base paint.
...but you could always experiment with tiny amounts and controlled environment...
...and then I disappeared in the mist...
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math
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I see, thanks for your reply 
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