doi:10.1038/nindia.2013.91 Published online 12 July 2013
Researchers have invented a new type of semiconductor nanocrystal, known as quantum dots, that are capable of emitting different colours ranging from green to red . These nanocrystals may find applications in various electronic displays.
Light-emitting quantum dots are nanoparticles with diameters smaller than about 10 nm. They absorb ultraviolet light and give off visible light, making them useful in bright video displays and extremely tiny devices that can locate specific genes in biological cells. However, pure quantum dots absorb the light that they emit and are unstable over long periods, whereas doped quantum dots emit only a single colour, which cannot be tuned.
Researchers overcame these problems by synthesizing manganese-doped zinc-sulphide–cadmium-sulphide alloy nanocrystals (known as manganese-doped semiconductor nanocrystals). They prepared solutions of these nanocrystals and poured the solutions over a thin polymer film.
The light-emitting properties of the nanocrystals were studied by irradiating these solutions with laser light and observing the emitted light under a microscope. The researchers recorded emissions from more than 1,000 nanocrystals, of which they analyzed 354 in detail. The nanocrystals emitted light with colors ranging from deep green to red.
To explain this wide color range, the researchers suggest that the color a quantum dot emits is determined by the energy levels of the manganese ions it contains. These energy levels are influenced by the electric field produced by the surrounding semiconductor atoms of the nanocrystals. They say that the colour can be tuned by controlling the location of the manganese ions in the nanocrystals.