#pdf #materials #paper on SrAl₂O₄ #phosphorescent pigments, finding that particle size doesn’t affect decay time, which decays from 250 mcd after 1' to 15 mcd after 30' (a factor of 8, so τ ≈ 15') for the bluish-green version, and from 280 mcd after 1' to 15 mcd after 30'. But this is not the standard zinc sulfide phosphor.
#pdf compares conventional copper-doped zinc sulfide #phosphorescent #materials to SrAl₂O₄ (under the trade name LumiNova). Zinc sulfide (ZnS:Cu) is said to have about an order of magnitude faster decay, with an “afterglow extinction” of about 200' rather than SrAl₂O₄'s 2000'. There's also a nice log-log graph of the exponential decay, showing a decrease from 200 mcd/m² at 1' to 1 mcd/m² at 50', which gives τ ≈ 9'. SrAl₂O₄’s afterglow lasts much longer not only because it decays more slowly but also because it starts out much brighter. Lots of tips on industrial pigment processing.
This #pdf #paper reports that zinc sulfide #phosphorescent #materials have a bandgap for ultraviolet radiation at 336 nm, and you can excite it with 325-nm light, although its photoluminescence spectrum has a strong peak at 396 nm and a weaker one at 478 nm, leading to the blue-green color we’re familiar with.