Why are blue light-emitting diodes so bright?
In the October issue of Nature Materials, a team of researchers propose a solution to the puzzle of why blue light-emitting diodes (LEDs) are so bright. Despite their huge commercial success, until now the reason for this unusual brightness has not been known. The material they are made from, indium gallium nitride, can only be fabricated to such a poor quality that it would not normally be expected to emit much light. Shigefusa Chichibu and colleagues have ingeniously used positron annihilation spectroscopy to show that the blue light emission originates from structures that consist of only a few atoms, which is what made them so difficult to observe in experiments. The authors propose that their results agree with an older model of structures formed from just three indium atoms in a chain, alternating with nitrogen, that is, In-N-In-N-In. In future, such tiny atomic arrangements might be created on purpose to achieve highly efficient light emission in other materials as well. Shuji N
