Infrared optical devices are used for night vision, astronomy and telecommunications. Most inorganic solids have very low energy vibrations because they are made with heavy atoms. For this reason, they can sustain electronic excitation in the infrared. The infrared optical properties of inorganic colloids become one of their special advantages compared to organic molecules. The novel infrared optical properties of the nanomaterials might lead to better and much cheaper infrared devices.
We study the physics of the infrared electronic transitions of semiconductor nanocrystals.
At long enough wavelength, the electronic excitation of quantum dots can become resonant with vibrations of the organic molecules at the surface of the nanoparticle and get quenched. This shortens the exciton lifetime and strongly reduces the photoluminescence quantum yield. However, for photodetection, it suffices to extract the carriers before exciton recombination. HgTe is a zero-gap bulk material, but Colloidal Quantum Dots of HgTe show a tunable infrared gap. With particles up to 12 nm in size, photocurrent detection and fluorescence covers the first atmospheric transparency range of 3-5 microns.