Conventional white LEDs suffer the same flaw. Their internal efficiency significantly falls with the injection current. Try to pump up the output power too much and you get an overall efficiency that’s not much better than fluorescent tubes. This is the so called "efficiency droop".

Improving on broadly emission tunable InGaN/GaN nanowire heterostructures, researchers at McGill University (Canada) came up, in 2011, with a phosphor-free device made of multiple InGaN insertions stacked in GaN nanowires, which does not suffer such limitations.

Although PL and TRPL studies had already been carried out on similar heterostructures, the team succeeded in extending the time window enough to be able to observe the strong power law shape of the photoluminescence decay.

Using a simple charge separation model involving a bright and a dark state, the scientists faithfully reproduced the data. The behaviour of both the recombination and separation rate (two parameters involved in the model) with the energy of emission is coherent with carrier radiative recombination occurring on In-rich nanocluster sites.

A full description of the study and the samples can be found in the journal Nanotechnology.