There were a couple of threads a day or so ago about glow in the dark paint. But if you use it, it actually does have to be charged with a light source, and will glow fairly bright for a while. It's not as good as replacing your old ones of course, but if you don't have the money, it's better than nothing.
If you have the night sights on it already, which by your "they don't glow anymore" statement, I'm going to surmise that you do, then ditto to the "you'll need to replace them" statements.
Check Gunbroker, ebay and even amazon. You'll find deals on XS Sights, Ameriglo and Tru Glo "night sights" that will glow.
The glow in the dark paints from GLow-on, Glowinc, and Brightsights will work in a pinch, but they do have to be "charged" with a UV light source for them to glow. If you have your gun in a drawer, in a purse, glovebox, etc, and not exposed to light, when you take out the gun to use it, the sights will still be dark. Things labeled "night sights" contain a radioactive material called Tritium and will glow on their own. Since the material is radioactive, you can't buy it to "Re-charge" your night sights.
Above link is a thread on a cheap glow in the dark alternative if you are not yet sure if having glowing night sights is absolutely necessary. If do you know for sure that you want night sights, you'd have to replace the existing sights with another set containing tritium and may as well save the extra money spent on the cheaper alternative discussed in above link.