Phosphor-free white: the prospects for green direct emitters

Energy efficiency has been the primary driving force for solid state lighting to replace wasteful incandescent lamps by light emitting diodes (LEDs). Recently, rising cost for rare earth metals has redoubled the push to also replace fluorescent and compact fluorescent lighting. Phosphors in fluorescent lamps heavily rely on rare earth metals and even first generation LEDs use such phosphors, albeit at much lower quantities. The role of phosphors to expand a narrow wavelength source into a wider spectrum is a very lossy process in itself and can be circumvented altogether by second generation LEDs, where the full visible solar spectrum is directly replicated by direct emitting LEDs. We here report progress of our work towards this goal, in particular by the development of high brightness direct emitting green group- III nitride LEDs.