One of the consequences of E=MC^2 is that there is a strong implication that energy can be converted directly into energy and vice versa.

Photons, although mass-less, have energy and can therefore be converted into matter under some circumstances.

I think you mean "directly into matter".

Yes. Thank you!

Apparently my well intentioned ramblings can be directly converted into brain farts.

I’ve always understood photons as being “stuff” in it’s all energy no mass state.

What is “stuff” as all matter no energy?

Probably any matter at absolute 0 would qualify? I think otherwise all mass has some excess of energy in it, I could be wrong.

Alternatively, possibly dark matter would qualify, although I am not sure either as we haven't even proven that it exists.

Wait, no, I was wrong. Matter and Energy are the same thing. Only nothing has no energy or matter.