Photon Gems are special gemstones made of crystallized photon particles that contain some major juju. Touch one of them, you never know what's going to happen. They are similar to chaos emeralds, but these photon gems come in a wide variety of colors and there are more than seven of them in existence. If they are all put together, they can be welded into the most dangerous weapon in the universe and beyond, the Photon Axe. Fortunately, if they all come together in one place, they scatter and disappear all over again. Unfortunately, if that one place covers the gems in a cosmic energy field, the field prevents the gems from scattering.
In the Dave Felis vs. Sly Cooper trilogy, the villains (except the Dragozaur Clan) are trying to get the Photon Gems so they can form the Photon Axe. If they succeed in forging the Photon Axe, they'll have the power to deconstruct an entire asteroid belt at the molecular level. Even gods, toons, and Seijuujins can be de-molecularized by the Photon Axe. Only a toon/human/Seijuujin hybrid like Brandon has the power to survive the Photon Axe's power and reduce it to Photon Gems (unless the god, toon, and seijuujin was zone-sensitive).