Quantum Dots Detect Long IR Wavelengths

A low-cost colloidal chemistry method has been used to prepare highly uniform batches of unusually large mercury telluride quantum dots. The investigation broadens the range of control that can be exerted on nanocrystal growth via synthesis methods and provides new materials that could lead to inexpensive detectors for thermal imaging cameras (ACS Nano 2014, DOI: 10.1021/nn503805h). Thermal imaging is widely used for nighttime surveillance and other military and civilian applications. The technology is based on detecting infrared radiation primarily in the 3- to 12-μm range. Common photodetectors for the application are expensive and use single crystals of indium antimonide and mercury cadmium telluride, as well as other materials requiring high-tech fabrication procedures. A team led by the University of Chicago’s Philippe Guyot-Sionnest has now shown that carefully controlling the concentration of the tellurium precursor, reaction temperature, and other parameters leads to selective formation of uniform HgTe crystals up to 20 nm in size. In contrast to earlier studies showing that colloidal HgTe quantum dots could detect IR light with wavelengths up to 7 μm, the new work extends the detection range to the 12 μm needed for complete thermal imaging.