Optoelectronic properties of dual emitting RNA-mediated colloidal PbSe nanostructures

This paper presents the optical and photophysical properties of RNA templated PbSe nanostructures in the presence of excess Pb2+. These particles exhibit an onset of absorption in the NIR range at about 1208 nm (0.97 eV) and display weak excitonic bands at 320 nm, 405 nm and 670 nm. The excitation of these particles by 670 nm light causes dual fluorescence in the red and NIR region peaking (range): at 770 nm (690-850 nm) and 1000 nm (850-1150 nm), respectively. The quantum efficiency of fluorescence in the red and NIR region were estimated to be 0.018 and 0.27, respectively. Fluorescence due to freshly prepared colloidal PbSe in the visible and NIR range is observed to have a fairly long lifetime of 320 ns and 31.8 ns, respectively unlike those of organic fluorophores emitting in this range. Aging of these particles leads to a change in morphology from QDs to nanotubes, which is associated with a decrease in absorption coefficient in the visible range along with an increase in absorption in the NIR region. These nanostructures become less emissive and depict a shorter emission lifetime. The poor absorption in the NIR range and a fairly intense fluorescence in the wavelength range of 850-1150 nm make these particles highly suitable for bioimaging of tissues.