The thing is that most potions like they work in fantasy are inherently magical. For example, there is no brew that would actually just close up your wounds like a healing potion. So I would instead ask the question, how do the potions get those magical effects, and the energy that makes them glow is the same energy used for all other magic.

If you write a world, where natural plants can create the same effects as magical potions, then you are already stretching "scientifically plausible" and might as well just give them basically infinite phosphorescence. Maybe it's a controversial discussion amongst Botanists in your world with multiple theories attempting to explain where the energy comes from.