IIRC/IIUC, GaN could only deal with UV or at most deep-ish blue, for both input and output, due to bandgap or whatever quantum reasons I don't understand. To create white light from light emitted by a GaN device, it needs to be downconverted into visible range by use of either phosphorous materials or a nanoparticle resembling them that are activated by blue light and emit its own light. On most white LEDs, this is done by that yellow goop of plastic material dabbed on top of blue LEDs.

Could this be like nanostructure based? Like nanoscale etching that messes with the light, created on top of UV LEDs?