Phosphorescent paints are kind of horrible, but glow powders work great. The hard part is getting them to stick. Tammy Cook-Endres suggested Elmer's Glue, and it works great. Washes off with water but dries strong and most importantly, clear. Make a slurry of the pigment and the glue and let to dry. Glow, Inc on Amazon sells a variety of the powders. They seem expensive but they are not so bad as 1/4 ounce is actually a lot phosphorescent powder for our purposes.
Fluorescent paint works better and is cheaper. You can get it from many paint supply stores. Bring a handheld UV lamp if you'd got one to try them out first. These seem pretty good.