A few details as further info, focusing mostly on the technical aspects:

It's considerably easier to decrease the band gap than to increase it. Decreasing it only requires that you insert some material to provide an intermediate band, while increasing it would likely need alloying it to force some structural change.

The material being in the right band gap is not enough. You need to make sure that it can be p-doped and n-doped, that its crystalline structure is stable even with some temperature variation. Ah, it should be also relatively straightforward to produce industrially.

Then you get the little gem that Nakamura found.