How to make glow in the dark pebbles? (that will glow several/many days/weeks)
Do you mean glow all night and/or without being exposed to light periodically? If so, I think the only answer is battery and LED. If not, covering pebbles with phosphorescent paint might be enough. Especially if you can point a UV lamp at them, which will not only cause them to fluoresce strongly while it's on but which will also quickly "pump them up" to their full stored-energy phosphorescent state.
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This phosphorescent aquarium gravel is made of a particularly bright material and is sealed against degradation by water. There are other, cheaper substances that will do the same. In any case, it would still require continuous pumping with a black light as orksecurity said.
Similar to ork' you either get some radioactive paint (very doubtful) or you make LED-lit pebbles from e.g. some kind of resin. Or you paint with something fluorescent and illuminate with UV. L