Could Green Lantern create Kryptonite?
Just thought I’d expand on what /u/gamer4maker has already (most excellently) here:
Short answer yes with an if, long answer no with a but.
Basically pre-Rebirth, if a Green Lantern had enough willpower they could create any energy source known to man, including Kryptonite radiation. Since Geoff Johns took over the Lanternverse things may have changed a little. It’s never been explicitly stated, but it’s never happened, and it appears the rules have been changed.
Anyway, on with my answer!