| The semi metal HgTe allows in principle continuous coverage in the infrared with colloidal quantum dots. While previous work demonstrated interesting properties in the near-infrared, we focus on the longer wavelength. We found that HgTe colloidal dots provide readily infrared photodetectors and fluorophores in the first mid-infrared band of atmospheric transparency from 3 to 5 microns with results now up to 7 microns. Some of the main optical properties are well described by a simple two-band k.p model, but we do not yet have a good understanding of the excited states. Striving to improve the materials and increasing the wavelength leads to interesting questions. 1) why are the nanoparticle solids so noisy? For photodetection, a limitation is the 1/f noise that seems ubiquitous in nanoparticle solid assembly. I will discuss our present understanding of the parameters that lower the noise. 2) Why is infared luminescence so weak? Concerning the fluorescence, the quantum efficiency drops precipitously at smaller energies, and this will be discussed in terms of coupling to ligands vibrations as well as intrinsic multiphonon relaxation processes. Eventually, as these problems get resolved, such materials could lead to a significant transformation of the thermal imaging and infrared communication technologies. |
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