I haven't seen anything so far that really works well enough to depend on, that can be easily applied by the end user.
I like tritium for night sights, but a properly fitted shotgun that has been used/practiced with/trained with enough so that it shoots where you look is the best bet in the long run.
Meprolight and Trijicon both make shotgun beads with tritium. They will likely require drilling and tapping to install as beads on many shotguns these days are pressed in rather than threaded. For traditionalists, plain gold beads are the most likely to gather any available light and reflect it to the shooter.
hth,
lpl/nc