What is the best base to use for luminous paint?

Question

I have luminous powders from ebay, those containing europium and glowing in various colors in the dark after being charged with visible or ultraviolet light. I would like to make them into paint by mixing them with a suitable paint base. I have seen luminous paint base offered for sale but at extravagant prices. Is there a more affordable and general solution? I think the main requirement is that the paint base should be weatherproof (if for use outdoors) and that it not absorb long-wave ultraviolet light (315-400mn), as this wavelength given off by the sun helps recharge the luminous pigment.

Edit: After looking more into this, I realized that fluorescent paint should have the same requirement as luminous paint, as both need exposure to long-wave UV. This site sells fluorescent paint that has an acrylic base. So a possible paint base is polyvinyl alcohol (white glue), though it may not be weather resistant. Shrinky Dinks, made of polystyrene, came in a variety impregnated with luminous zinc sulfide. So protecting a luminous painted surface with a layer of plastic should work.

Answer 1

I'd try polyurethane varnishes.
They are weatherproof, contrary to standard acrylic varnishes, they are transparent, but may absorb a bit of UV light, as UV is sometimes a catalyst to the reaction to form them (source : wikipedia) (only a guess here, as I didn't find valuable PU absorption spectrum). It is also stated that polyurethanes with isocyanates react with UV light and it discolours them over time, so if you can, try isocyanate-free polyurethane.
Anyway, it is a very common outer coating protection for wood, so it is not very expensive (found some at 20 €/$ for 250ml).
You could give it a try and see how it works for you.