Can phosphors ever be completely clear?
No. All afterglow phosphors for coatings and plastics are opaque inorganic solids. So the best you’ll get is white. There are a few translucent organic afterglow materials, water based naphthalin derivatives mainly, but they’re only used in microbiology for labelling specimens and fizzle out quite quickly. These are no good for coatings. There are also chemiluminescent materials which are very bright for three or four hours after two clear liquids mix, but then they fade away. Both of these would not be usable in typical coatings for health and safety reasons.
