| To make a phosphor you generally need a matrix and an activator. For the matrix here you need some boron oxide mass. As activator. unusually you add some organic pigment molecules. Fluorescein works very well.
To create boron oxide matrix you just melt a bit of boric acid. Use aluminium foil or thin aluminium plate as a base, heat the acid in the flame slowly. It will bubble decomposing to boron oxide and water, then will stop bubbling leaving a glassy mass. You need just add a few grains of fluorescein or a drop of fluorescein solution activator to the acid before melting. Do not overheat, avoiding fulorescein to char and turn brown.
When cooled, you will end up with greenish glassy mass. It is a phosphor but with some unusual properties, some kind of scientific curiosity. When charged with a bright light, it afterglow for a few seconds with a green light. What is unusual compared to regular persistent phosphors like zinc sulphide or strontium aluminate, it does not saturate at all, when charged with a bright xenon flash for example, it will afterglow *very* bright. Some say it does not phosphoresce as usual inorganic persistent phosphors, but what you see is in fact a fluorescence delayed by a very unusual amount of time!
Some other compounds work as acitivators too. If I remember right, an old drug of antipyrene gives blue glow. Also never tried, but probably fluorescein relatives rodamine and eosine may give orange and pink glow? Or will they decompose?
Both boric acid and fulorecsein are non-toxic within a reason and are easy to get, boric acid is even available at pharmacies where I live)
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