Colloidal nanocrystals

Blinking colloidal nanocrystals is a phenomenon observed during studies of single colloidal nanocrystals that show that they randomly turn their photoluminescence on and off even under continuous light illumination. This has also been described as luminescence intermittency. Similar behavior has been observed in crystals made of other materials. For example, porous silicon also exhibits this affect.

Colloidal nanocrystals are a new class of optical materials that essentially constitute a new form of matter that can be considered as "artificial atoms." Like atoms, they have discrete optical energy spectra that are tunable over a wide range of wavelengths. The desired behavior and transmission directly correlates to their size. To change the emitted wavelength, the crystal is grown larger or smaller. Their electronic and optical properties can be controlled by this method. For example, to change the emission from one visible wavelength to another simply use a larger or smaller grown crystal. However, this process would not be effective in conventional semiconductors such as gallium arsenide.

The nanocrystal size controls a widely tunable absorption band resulting in widely tunable emission spectra. This tunability combined with the optical stability of nanocrystals and the great chemical flexibility in the nanocrystal growth have resulted in the widespread nanocrystal applications in use today. Practical device applications range from low-threshold lasers to solar cells and biological imaging and tracking. Producing a specific type of luminescence known as photoluminescence nanocrystals show quite high quantum efficiency of up to 70% at room temperature. The missing 30% efficiency turns out to be an intrinsic property of nanocrystals.

Studies of single colloidal nanocrystals show that they randomly turn their photoluminescence on and off even under continuous light illumination. This tends to hinder progress for engineers and scientists who study single colloidal nanocrystals and try to use their fluorescent properties for biological imaging or lasing.

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