Nanocrystals glow red, green
doi:10.1038/nindia.2011.75 Published online 30 May 2011
Researchers have designed new ultrasmall alloy nanocrystals that could be potentially useful for solar cells, light-emitting diodes and biomedical applications. The nanocrystals absorb visible and ultraviolet light, and emit visible light.
Light-emitting semiconductor nanocrystals with tunable emission properties are of great interest for applications in photovoltaics, optoelectronics and biology. However, these applications require nanocrystals that are small and cadmium-free (that is, nontoxic), which are currently not available.
To make such nanocrystals, the researchers added a selenium precursor molecule to a mixture of zinc, indium and copper salts. This produced copper-doped zinc indium selenide alloy nanocrystals with a fixed size of around 2.5 nm.
The researchers varied the ratio of zinc, indium and selenium ions on the surface of the nanocrystals during the synthesis process. This produced a varying composition of surface cations that could be excited with visible light. Varying the cation composition allowed the nanocrystal's emission properties to be tuned from green to red wavelengths.
Analysis confirmed that zinc ions replaced most of the indium ions on the surface of the nanocrystals and that the inner core composition remained mostly the same. The nanocrystals are unique because they retain their small fixed size during wavelength tuning.
The nanocrystals are ultrasmall, cadmium-free and absorb visible and ultraviolet light. This makes them suitable candidates for a variety of applications following proper surface functionalization.
"These new materials could be useful for bioimaging, light-emitting devices and photovoltaic cells," says lead researcher Narayan Pradhan.
- Sarkar, S. et al. Ultrasmall color-tunable copper-doped ternary semiconductor nanocrystal emitters. Angew. Chem. Int. Ed. 50, 1-6 (2011) | Article |