Novel tweak for nanocrystals
doi:10.1038/nindia.2010.129 Published online 22 September 2010
Researchers have successfully used oxide nanocrystals of transition metal ions to dope semiconductor nanocrystals. The resulting semiconductor nanocrystals showed better stability and emission properties than nano-sized quantum dots, and will find use in light-emitting devices and biological labelling.
To insert transition metal ions into nanocrystals, the researchers first took 'host' semiconductor nanocrystals of zinc sulphide, zinc selenide, and their alloys. Then they heated these host nanocrystals with oxide nanocrystals containing transition metal ions of copper and manganese in a reaction flask.
The heating process caused the oxide nanocrystals to release their metal ions onto the surface of hosts, where they became buried as the host nanocrystals grew more outer layers. The emission properties of these doped nanocrystals were then studied through irradiation with ultraviolet and visible light.
Compared with other doped nanocrystals, these nanocrystals displayed longer excited state lifetimes and tunable emission properties. The excited state lifetime was of the order of milliseconds in the manganese-doped system and microseconds in the copper-doped system. These nanocrystals also have no (or minimal) self-absorption, making them better than existing nanomaterials for use in light-emitting devices.
"The long excited state lifetimes of these nanocrystals makes them ideal for use as energy transfer donors with different organic dyes, which have been used to measure small distances in various biological events," says lead researcher Narayan Pradhan. This method is simple and can be used to make a wide variety of doped nanocrystals, thus avoiding the use of cadmium, a heavy metal that is well-known to be carcinogenic.
The authors of this work are from: Centre for Advanced Materials and the Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata; Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, and Radiochemistry Division, Babha Atomic Research Centre, Mumbai, India.
- Karan, S. N. et al. Doping transition metal (Mn or Cu) ions in semiconductor nanocrystals. J. Phys. Chem. Lett. 1, 2863-2866 (2010)